Age associations with Tacrolimus and Mycophenolic Acid Pharmacokinetics in Stable Black and White Kidney Transplant Recipients: Implications for Health Inequities

Tacrolimus and mycophenolic acid (MPA) provide maintenance immunosuppression and is dosed empirically in elderly kidney transplant recipients (KTR) resulting in health inequities. Limited immunosuppressive pharmacokinetics is available comparing adult ages. This secondary analysis compared tacrolimus and MPA pharmacokinetics and adverse effects (AE) among young, middle-age and elderly Black and White KTR. 12-hour tacrolimus and MPA pharmacokinetics with AE evaluation were conducted in 67 stable KTR ≥6-months post-transplant. Tacrolimus regimens were adjusted to target troughs. MPA regimens were adjusted using clinical response. Participants were: young: ≤ 40 years; middle age:40-60 and elderly>60. Non- compartmental pharmacokinetic analysis determined area under the concentration-time curve 0-12hours (AUC_0-12 ), Clearance (CL), CL/BMI with 0-hour troughs. MPA enterohepatic recirculation (EHR), MPA-AUC_6- 12/MPA-AUC_0-12 and MPAG-AUC_0-12 /MPA-AUC_0-12 were determined. Univariate ANOVA was conducted using SAS V 9.4. No group differences were noted for e-GFR, MPA and TAC doses. EHR was reduced in elderly with decreased MPA-AUC_6-12 /MPA-AUC_0-12 (P=0.049) and increased MPAG-AUC_0-12 /MPA-AUC_0-12 (P=0.028). MPA troughs(P=0.045) were reduced in the elderly. Tacrolimus CL/BMI(P=0.043) was reduced in elderly. For therapeutic MPA AUC_0-12 :30-60 mg●hr/L, 34.3% KTR achieved this target with 55.2% > therapeutic range. 77.6% KTR were in the tacrolimus AUC_0-12 target:100-190ng●hr/ml and 19.4% < this range with no age relationship. 44% young, 26% middle-age and 7.8% elderly achieved target AUC_0-12 for both medications(P=0.036). Neurologic AE were manifested in elderly(P=0.014). Immunosuppressive pharmacokinetics demonstrated age-related differences with reduced tacrolimus clearance and MPA enterohepatic recirculation and increased neurologic AE in elderly. This immunosuppressive regimen may require age-adjusted individualization to optimize allograft function.

Comparison of P-glycoprotein function in peripheral blood mononuclear cells ex vivo in stable Black and White male and female kidney transplant recipients

Kidney allograft survival remains poorer in Black compared to White recipients due to racial differences in calcineurin inhibitor (CNI) pharmacology. P-glycoprotein (P-gp), an ABC efflux transporter expressed in peripheral blood mononuclear cells (PBMCs), modulates CNI pharmacokinetics and intracellular pharmacology. This study investigated P-gp function in PBMC ex vivo at 0 (trough), 4, 8, and 12 h in stable Black and White male and female kidney transplant recipients (n = 67) receiving tacrolimus and mycophenolic acid. Tacrolimus doses were adjusted to troughs of 4-10 ng/ml. P-gp function was quantified with flow cytometric measurement of cyclosporine (CYA; 2.5 μM)-reversible efflux of P-gp substrate, 3,3'-Diethyloxacarbocyanine iodide by determining the percentage change of mean fluorescent intensity (MFI) with CYA (% ΔMFI). The composite parameter of area under the concentration versus time (AUC)_0-12h % ΔMFI estimated P-gp function. Data analysis examined race, sex, and race-sex associations to P-gp function. A secondary aim analyzed ABCB1 genotypes: 1236C>T (rs1128503), 2677G>T/A (rs2032582), 3435C>T (rs1045642), and P-gp function. P-gp function (% ΔMFI) was higher in White patients at troughs (p = 0.031) compared to Black counterparts with similar trends at 4 and 8 h. Reduced AUC_0-12h % ΔMFI was noted in Black recipients (N = 32) compared with Whites (N = 35, p = 0.029) with notable pairwise adjusted differences between Black and White women (p = 0.021). Higher AUC_0-12h % ΔMFI was associated with ABCB1 2677 TT compared to GG variants (p = 0.035). The AUC_0-12h % ΔMFI was greater in White than Black subjects. P-gp function was higher at troughs in White subjects and differed between race-sex groups. P-gp function in PBMC may influence intracellular tacrolimus exposure and inter-relating pharmacodynamic responses which may support race and sex pharmacologic differences.

Race and sex associations with tacrolimus pharmacokinetics in stable kidney transplant recipients

Study Objective

This study investigated race and sex differences in tacrolimus pharmacokinetics and pharmacodynamics in stable kidney transplant recipients.

Design and Setting

A cross‐sectional, open‐label, single center, 12‐h pharmacokinetic‐pharmacodynamic study was conducted. Tacrolimus pharmacokinetic parameters included area under the concentration‐time curve (AUC_0–12), AUC_0–4, 12‐h troughs (C_12 h), maximum concentrations (C_max), oral clearance (Cl), with dose‐normalized AUC_0–12, troughs, and C_max with standardized adverse effect scores. Statistical models were used to analyze end points with individual covariate‐adjustment including clinical factors, genotypic variants CYP3A5*3, CYP3A5*6, CYP3A5*7(CYP3A5*3*6*7) metabolic composite, and ATP binding cassette gene subfamily B member 1 (ABCB1) polymorphisms.

Patients

65 stable, female and male, Black and White kidney transplant recipients receiving tacrolimus and mycophenolic acid ≥6 months post‐transplant were evaluated.

Measurements and Main Results

Black recipients exhibited higher tacrolimus AUC_0–12 (Race: p = 0.005), lower AUC* (Race: p < 0.001; Race × Sex: p = 0.068), and higher Cl (Race: p < 0.001; Sex: p = 0.066). Greater cumulative (Sex: p < 0.001; Race × Sex: p = 0.014), neurologic (Sex: p = 0.021; Race × Sex: p = 0.005), and aesthetic (Sex: p = 0.002) adverse effects were found in females, with highest scores in Black women. In 84.8% of Black and 68.8% of White patients, the target AUC_0–12 was achieved (p = 0.027). In 31.3% of White and 9.1% of Black recipients, AUC_0–12 was <100 ng‧h/ml despite tacrolimus troughs in the target range (p = 0.027). The novel CYP3A5*3*6*7 metabolic composite was the significant covariate accounting for 15%–19% of tacrolimus variability in dose (p = 0.002); AUC_0–12 h* (p < 0.001), and Cl (p < 0.001).

Conclusions

Tacrolimus pharmacokinetics and adverse effects were different among stable kidney transplant recipient groups based upon race and sex with interpatient variability associated with the CYP3A5*3*6*7 metabolic composite. More cumulative, neurologic, and aesthetic adverse effects were noted among females. Tacrolimus regimens that consider race and sex may reduce adverse effects and enhance allograft outcomes by facilitating more patients to achieve the targeted AUC_0–12 h.

Association of ABCC2 Haplotypes to Mycophenolic Acid Pharmacokinetics in Stable Kidney Transplant Recipients

Mycophenolic acid exhibits significant interpatient pharmacokinetic variability attributed to factors including race, sex, concurrent medications, and enterohepatic circulation of the mycophenolic acid glucuronide metabolite to mycophenolic acid. This conversion by enterohepatic circulation is mediated by the multidrug resistance-associated protein 2, encoded by ABCC2. This study investigated ABCC2 haplotype associations with mycophenolic acid pharmacokinetics in 147 stable kidney transplant recipients receiving mycophenolic acid in combination with calcineurin inhibitors. The role of the ABCC2 genotypes -24C>T (rs717620), 1249C>T (rs2273697), and 3972C>T (rs3740066) were evaluated in prospective, cross-sectional pharmacokinetic studies of stable recipients receiving mycophenolic acid and either tacrolimus or cyclosporine. Haplotype phenotypic associations with mycophenolic acid pharmacokinetic parameters were computed using THESIAS (v. 3.1). Four ABCC2 haplotypes with estimated frequencies greater than 10% were identified (H1:CGC [wild type], H9:CGT, H2:CAC, H12:TGT). There were no differences in haplotype frequencies by either race or sex. There were significant associations of pharmacokinetic parameters with ABCC2 haplotypes for mycophenolic acid clearance (L/h), mycophenolic acid AUC_0-12h (mg·h/L), and the ratio of mycophenolic acid glucuronide to mycophenolic acid AUC_0-12h . The wild-type haplotype ABCC2 CGC had greater mycophenolic acid AUC_0-12h (P = .017), slower clearance (P = .013), and lower mycophenolic acid glucuronide to mycophenolic acid AUC_0-12h ratio (P = .047) compared with the reduced function ABCC2 haplotype CGT. These differences were most pronounced among patients receiving tacrolimus cotreatment. No phenotypic associations were found with the cyclosporine-mycophenolic acid regimen. Variation in ABCC2 haplotypes contributes to subtherapeutic mycophenolic acid exposure and influences interpatient variability in pharmacokinetic phenotypes based on concurrent calcineurin inhibitor treatment.

Beyond Single Nucleotide Polymorphisms: CYP3A5∗3∗6∗7 Composite and ABCB1 Haplotype Associations to Tacrolimus Pharmacokinetics in Black and White Renal Transplant Recipients

Interpatient variability in tacrolimus pharmacokinetics is attributed to metabolism by cytochrome P-450 3A5 (CYP3A5) isoenzymes and membrane transport by P-glycoprotein. Interpatient pharmacokinetic variability has been associated with genotypic variants for both CYP3A5 or ABCB1. Tacrolimus pharmacokinetics was investigated in 65 stable Black and Caucasian post-renal transplant patients by assessing the effects of multiple alleles in both CYP3A5 and ABCB1. A metabolic composite based upon the CYP3A5 polymorphisms: ^∗3(rs776746), ^∗6(10264272), and ^∗7(41303343), each independently responsible for loss of protein expression was used to classify patients as extensive, intermediate and poor metabolizers. In addition, the role of ABCB1 on tacrolimus pharmacokinetics was assessed using haplotype analysis encompassing the single nucleotide polymorphisms: 1236C > T (rs1128503), 2677G > T/A(rs2032582), and 3435C > T(rs1045642). Finally, a combined analysis using both CYP3A5 and ABCB1 polymorphisms was developed to assess their inter-related influence on tacrolimus pharmacokinetics. Extensive metabolizers identified as homozygous wild type at all three CYP3A5 loci were found in 7 Blacks and required twice the tacrolimus dose (5.6 ± 1.6 mg) compared to Poor metabolizers [2.5 ± 1.1 mg (P < 0.001)]; who were primarily Whites. These extensive metabolizers had 2-fold faster clearance (P < 0.001) with 50% lower AUC^∗ (P < 0.001) than Poor metabolizers. No differences in C_{12 h} were found due to therapeutic drug monitoring. The majority of blacks (81%) were classified as either Extensive or Intermediate Metabolizers requiring higher tacrolimus doses to accommodate the more rapid clearance. Blacks who were homozygous for one or more loss of function SNPS were associated with lower tacrolimus doses and slower clearance. These values are comparable to Whites, 82% of who were in the Poor metabolic composite group. The ABCB1 haplotype analysis detected significant associations of the wildtype 1236T-2677T-3435T haplotype to tacrolimus dose (P = 0.03), CL (P = 0.023), CL/LBW (P = 0.022), and AUC^∗ (P = 0.078). Finally, analysis combining CYP3A5 and ABCB1 genotypes indicated that the presence of the ABCB1 3435 T allele significantly reduced tacrolimus clearance for all three CPY3A5 metabolic composite groups. Genotypic associations of tacrolimus pharmacokinetics can be improved by using the novel composite CYP3A5^∗3^∗4^∗5 and ABCB1 haplotypes. Consideration of multiple alleles using CYP3A5 metabolic composites and drug transporter ABCB1 haplotypes provides a more comprehensive appraisal of genetic factors contributing to interpatient variability in tacrolimus pharmacokinetics among Whites and Blacks.

The impact of systematic review of status 7 patients on the kidney transplant waitlist

Background

Increased morbidity and mortality are well documented in Status 7(inactive list) patients. Delays in transplantation secondary to prolonged periods on inactive status also negatively impacts transplant outcomes. We developed an effective system to reduce the proportion of status 7 patients on our kidney transplant waitlist. This can easily be reproduced by other transplant centers since concerns about Status 7 list size are commonplace.

Methods

Meetings of a dedicated status 7 focus group were undertaken biweekly beginning in April 2016, each lasting for 1 hour or less. The group was led by a transplant physician and comprised of members from all disciplines of the kidney transplant department. Individual patient barriers to activation were systematically evaluated and action plans were developed to overcome those. The formal meetings were supplemented by updates to an electronic database accessible to all members of the team.

Results

In the first 2 years of the program, we were able to activate and eventually transplant 18% of the formerly inactive patients. Forty percent of all inactive patients were removed from the waitlist due to one or more unsurmountable barriers. The median time patients stayed inactive on the waitlist was shortened from 1344 days at the start of this initiative to 581 days at the end.

Conclusion

This strategy of systematic reevaluation of status 7 patients resulted in successful disposition of a substantial number of inactive patients. Further, waitlist time was reduced and transplantation expedited for the appropriate individuals. This approach could easily be adapted by other transplant centers with minimum utilization of resources.

Influence of Calcineurin Inhibitor and Sex on Mycophenolic Acid Pharmacokinetics and Adverse Effects Post-Renal Transplant

Tacrolimus or cyclosporine is prescribed with mycophenolic acid posttransplant and contributes to interpatient variability in mycophenolic acid pharmacokinetics and response. Cyclosporine inhibits enterohepatic circulation of the metabolite mycophenolic acid glucuronide, which is not described with tacrolimus. This study investigated mycophenolic acid pharmacokinetics and adverse effects in stable renal transplant recipients and the association with calcineurin inhibitors, sex, and race. Mycophenolic acid and mycophenolic acid glucuronide area under the concentration-time curve from 0 to 12 hours (AUC_0-12h ) and apparent clearance were determined at steady state in 80 patients receiving cyclosporine with mycophenolate mofetil and 67 patients receiving tacrolimus with mycophenolate sodium. Gastrointestinal adverse effects and hematologic parameters were evaluated. Statistical models evaluated mycophenolic acid pharmacokinetics and adverse effects. Mycophenolic acid AUC_0-12h was 1.70-fold greater with tacrolimus (68.9 ± 30.9 mg·h/L) relative to cyclosporine (40.8 ± 17.6 mg·h/L); P < .001. Target mycophenolic acid AUC_0-12h of 30-60 mg·h/L was achieved in 56.3% on cyclosporine compared with 34.3% receiving tacrolimus (P < .001). Mycophenolic acid clearance was 48% slower with tacrolimus (10.6 ± 4.7 L/h) relative to cyclosporine (20.5 ± 10.0 L/h); P < .001. Enterohepatic circulation occurred less frequently with cyclosporine (45%) compared with tacrolimus (78%); P < 0.001; with a 2.9-fold greater mycophenolic acid glucuronide AUC_0-12h to mycophenolic acid AUC_0-12h ratio (P < .001). Race did not affect mycophenolic acid pharmacokinetics. Gastrointestinal adverse effect scores were 2.2-fold higher with tacrolimus (P < .001) and more prominent in women (P = .017). Lymphopenia was more prevalent with tacrolimus (52.2%) than cyclosporine (22.5%); P < 0.001. Calcineurin inhibitors and sex contributed to interpatient variability in mycophenolic acid pharmacokinetics and adverse effects post-renal transplant, which could be attributed to differences in enterohepatic circulation.

The impact of tacrolimus exposure on extrarenal adverse effects in adult renal transplant recipients

AIMS

Tacrolimus has been associated with notable extrarenal adverse effects (AEs), which are unpredictable and impact patient morbidity. The association between model-predicted tacrolimus exposure metrics and standardized extrarenal AEs in stable renal transplant recipients was investigated and a limited sampling strategy (LSS) was developed to predict steady-state tacrolimus area under the curve over a 12-h dosing period (AUC_ss,0-12h ).

METHODS

All recipients receiving tacrolimus and mycophenolic acid ≥6 months completed a 12-h cross-sectional observational pharmacokinetic-pharmacodynamic study. Patients were evaluated for the presence of individual and composite gastrointestinal, neurological, and aesthetic AEs during the study visit. The associations between AEs and tacrolimus exposure metrics generated from a published population pharmacokinetic model were investigated using a logistic regression analysis in NONMEM 7.3. An LSS was determined using a Bayesian estimation method with the same patients.

RESULTS

Dose-normalized tacrolimus AUC_ss,0-12h and apparent clearance were independently associated with diarrhoea, dyspepsia, insomnia and neurological AE ratio. Dose-normalized tacrolimus maximum concentration was significantly correlated with skin changes and acne. No AE associations were found with trough concentrations. Using limited sampling at 0, 2h; 0, 1, 4h; and 0, 1, 2, 4h provided a precise and unbiased prediction of tacrolimus AUC (root mean squared prediction error < 10%), which was not well characterized using trough concentrations only (root mean squared prediction error >15%).

CONCLUSIONS

Several AEs (i.e. diarrhoea, dyspepsia, insomnia and neurological AE ratio) were associated with tacrolimus dose normalized AUC_ss,0-12h and clearance. Skin changes and acne were associated with dose-normalized maximum concentrations. To facilitate clinical implementation, a LSS was developed to predict AUC_ss,0-12h values using sparse patient data to efficiently assess projected immunosuppressive exposure and potentially minimize AE manifestations.

Tacrolimus Population Pharmacokinetics and Multiple CYP3A5 Genotypes in Black and White Renal Transplant Recipients

Tacrolimus exhibits inter-patient pharmacokinetic variability attributed to CYP3A5 isoenzymes and the efflux transporter, P-glycoprotein. Most black renal transplant recipients require higher tacrolimus doses compared to whites to achieve similar troughs when race-adjusted recommendations are used. An established guideline provides tacrolimus genotype dosing recommendations based on CYP3A5*1(W/T) and loss of protein function variants: CYP3A5*3 (rs776746), CYP3A5*6 (rs10264272), CYP3A5*7 (rs41303343) and may provide more comprehensive race-adjusted dosing recommendations. Our objective was to develop a tacrolimus population pharmacokinetic model evaluating demographic, clinical, and genomic factors in stable black and white renal transplant recipients. A secondary objective investigated race-based tacrolimus regimens and genotype-specific dosing. Sixty-seven recipients receiving oral tacrolimus and mycophenolic acid ≥6 months completed a 12-hour pharmacokinetic study. CYP3A5*3,*6,*7 and ABCB1 1236C>T, 2677G>T/A, 3435C>T polymorphisms were characterized. Patients were classified as extensive, intermediate, and poor metabolizers using a novel CYP3A5*3*6*7 metabolic composite. Modeling and simulation was performed with computer software (NONMEM 7.3, ICON Development Solutions; Ellicott City, Maryland). A 2-compartment model with first-order elimination and absorption with lag time best described the data. The CYP3A5*3*6*7 metabolic composite was significantly associated with tacrolimus clearance (P value < .05), which was faster in extensive (mean: 45.0 L/hr) and intermediate (29.5 L/hr) metabolizers than poor metabolizers (19.8 L/hr). Simulations support CYP3A5*3*6*7 genotype-based tacrolimus dosing to enhance general race-adjusted regimens, with dose increases of 1.5-fold and 2-fold, respectively, in intermediate and extensive metabolizers for comparable exposures to poor metabolizers. This model offers a novel approach to determine tacrolimus dosing adjustments that maintain comparable therapeutic exposure between black and white recipients with different CYP3A5 genotypes.

Utility of Serial Protocol Biopsies Performed After 1 Year in Predicting Long-Term Kidney Allograft Function According to Histologic Phenotype

OBJECTIVES

Prognostic implications of early protocol biopsies have been studied; however, the value of late protocol biopsy in predicting graft outcome has not been well defined. Here, we compared the effects of early and late protocol biopsy histologic findings in stable kidney allografts and aimed to understand the significance of "borderline" rejection on allograft function.

MATERIALS AND METHODS

We studied 261 biopsies from 159 renal transplant recipients who were on a steroid-free, calcineurin inhibitor and mycophenolate mofetil regimen and who received transplants between 2004 and 2012 with mean follow-up of 5 years. Early (between 3 and 9 mo) and subsequent late (between 12 and 24 mo) protocol biopsies were performed. Biopsies were classified as normal, interstitial fibrosis and/or tubular atrophy, subclinical acute rejection with interstitial fibrosis and/or tubular atrophy, and borderline rejection with interstitial fibrosis and/or tubular atrophy. A linear mixed-effects model was used to determine the effects of early and late protocol biopsies on estimated glomerular filtration rate changes, with baseline time for estimated glomerular filtration rate fixed at 12 months.

RESULTS

The adjusted model showed that estimated glomerular filtration rate at 3 months, donor age, delayed graft function, and early protocol biopsies were associated with baseline estimated glomerular filtration rate at 12 months. Estimated glomerular filtration rate changes over time were associated with findings of interstitial fibrosis and/or tubular atrophy at early biopsy and subclinical acute rejection and borderline rejection at late biopsy. At last follow-up, final estimated glomerular filtration rate was significantly associated with interstitial fibrosis and/or tubular atrophy at early biopsy and with subclinical acute rejection at late biopsy.

CONCLUSIONS

Although early protocol biopsy predicted baseline estimated glomerular filtration rate, late biopsy was important for predicting changes in function over time. In addition, a diagnosis of "borderline" rejection on protocol biopsies predicted long-term graft function.

An observational study of the quality of care for chronic kidney disease: a Buffalo and Albany, New York metropolitan area study

Background

The database of a major regional health insurer was employed to identify the number and frequency of covered patients with chronic kidney disease (CKD). We then examined the characteristics of their care as defined, in part, by the frequency of physician visits and specialty referral, the characteristics of laboratory testing and total costs as indices of the quality of care of the subject population.

Methods

This retrospective, cross-sectional study analyzed insurance claims, laboratory results and medication prescription data. Patients with two estimated glomerular filtration rate readings below 60 ml/min/1.73 m² (n = 20,388) were identified and classified by CKD stage.

Results

The prevalence of CKD stages 3a and above was 12 %. Vascular comorbidities were common with prevalence increasing steadily from stage 3a through stage 5. Only 55.6 % of stage 4 CKD patients had claims for nephrology visits within one year of their index date. Fifty-nine percent of patients had claims for renin-angiotensin system (RAS) blockers. Twenty-five percent of patients in stage 3a CKD filled a prescription for non-steroidal anti-inflammatory drugs. Fifty-two percent of patients who developed end-stage renal disease received their first dialysis treatment as inpatients.

Conclusions

The pattern of medical practice observed highlights apparent deficiencies in the care of CKD patients including inappropriate medication use, delayed nephrology referral, and a lack of preparation for dialysis. This study shows the potential value of using large patient databases available through insurers to assess and likely improve regional CKD care.

Influence of sex and race on mycophenolic acid pharmacokinetics in stable African American and Caucasian renal transplant recipients

BACKGROUND AND OBJECTIVES

No evaluation of sex and race influences on mycophenolic acid (MPA) pharmacokinetics and adverse effects (AEs) during enteric-coated mycophenolate sodium (ECMPS) and tacrolimus immunosuppression are available. The primary objective of this study was to investigate the influence of sex and race on MPA and MPA glucuronide (MPAG) pharmacokinetics in stable renal transplant recipients receiving ECMPS and tacrolimus

METHODS

The pharmacokinetics of MPA and MPAG and their associated gastrointestinal AEs were investigated in 67 stable renal transplant recipients: 22 African American males (AAMs), 13 African American females (AAFs), 16 Caucasian males (CMs), and 16 Caucasian females (CFs) receiving ECMPS and tacrolimus. A validated gastrointestinal AE rating included diarrhea, dyspepsia, vomiting, and acid-suppressive therapy was completed. Apparent clearance, clearance normalized to body mass index (BMI), area under the concentration-time curve from time zero to 12 h (AUC12) and dose-normalized AUC12 (AUC*) were determined using a statistical model that incorporated gastrointestinal AE and clinical covariates.

RESULTS

Males had more rapid apparent MPA clearance (CMs 13.8 ± 6.27 L/h vs. AAMs 10.2 ± 3.73 L/h) than females (CFs 8.70 ± 3.33 L/h and AAFs 9.71 ± 3.94 L/h; p = 0.014) with a race-sex interaction (p = 0.043). Sex differences were observed in MPA clearance/BMI (p = 0.033) and AUC* (p = 0.033). MPA AUC12 was greater than 60 mg·h/L in 57 % of renal transplant recipients (RTR) with 71 % of patients demonstrating gastrointestinal AEs and a higher score noted in females. In all patients, females exhibited 1.40-fold increased gastrointestinal AE scores compared with males (p = 0.024). Race (p = 0.044) and sex (p = 0.005) differences were evident with greater MPAG AUC12 in AAFs and CFs.

CONCLUSION

Sex and race differences were evident, with females having slower MPA clearance, higher MPAG AUC12, and more severe gastrointestinal AEs. These findings suggest sex and race should be considered during MPA immunosuppression.

Association of Extrarenal Adverse Effects of Posttransplant Immunosuppression With Sex and ABCB1 Haplotypes

Extrarenal adverse effects (AEs) associated with calcineurin inhibitor (CNI) and mycophenolic acid (MPA) occur frequently but are unpredictable posttransplant complications. AEs may result from intracellular CNI accumulation and low activity of P-glycoprotein, encoded by the ABCB1 gene. Since ABCB1 single nucleotide polymorphisms (SNPs) and sex influence P-glycoprotein, we investigated haplotypes and extrarenal AEs. A prospective, cross-sectional study evaluated 149 patients receiving tacrolimus and enteric coated mycophenolate sodium or cyclosporine and mycophenolate mofetil. Immunosuppressive AE assessment determined individual and composite gastrointestinal, neurologic, aesthetic, and cumulative AEs. Lipids were quantitated after 12-hour fast. ABCB1 SNPs: c.1236C>T (rs1128503), c.2677G>T/A (rs2032582), and c.3435C>T (rs1045642) were determined with haplotype associations computed using the THESIAS program, and evaluated by immunosuppression, sex and race using multivariate general linear models. Tacrolimus patients exhibited more frequent and higher gastrointestinal AE scores compared with cyclosporine with association to CTT (P = 0.018) and sex (P = 0.01). Aesthetic AE score was 3 times greater for cyclosporine with TTC haplotype (P = 0.005). Females had higher gastrointestinal (P = 0.022), aesthetic (P < 0.001), neurologic (P = 0.022), and cumulative AE ratios (P < 0.001). Total cholesterol (TCHOL), low-density lipoproteins (LDL), and triglycerides were higher with cyclosporine. The TTC haplotype had higher TCHOL (P < 0.001) and LDL (P = 0.005). Higher triglyceride (P = 0.034) and lower high-density lipoproteins (P = 0.057) were associated with TTT with sex-adjusted analysis. ABCB1 haplotypes and sex were associated with extrarenal AEs. Using haplotypes, certain female patients manifested more AEs regardless of CNI. Haplotype testing may identify patients with greater susceptibility to AEs and facilitate CNI individualization.

Validity and reliability of a novel immunosuppressive adverse effects scoring system in renal transplant recipients

Background

After renal transplantation, many patients experience adverse effects from maintenance immunosuppressive drugs. When these adverse effects occur, patient adherence with immunosuppression may be reduced and impact allograft survival. If these adverse effects could be prospectively monitored in an objective manner and possibly prevented, adherence to immunosuppressive regimens could be optimized and allograft survival improved. Prospective, standardized clinical approaches to assess immunosuppressive adverse effects by health care providers are limited. Therefore, we developed and evaluated the application, reliability and validity of a novel adverse effects scoring system in renal transplant recipients receiving calcineurin inhibitor (cyclosporine or tacrolimus) and mycophenolic acid based immunosuppressive therapy.

Methods

The scoring system included 18 non-renal adverse effects organized into gastrointestinal, central nervous system and aesthetic domains developed by a multidisciplinary physician group. Nephrologists employed this standardized adverse effect evaluation in stable renal transplant patients using physical exam, review of systems, recent laboratory results, and medication adherence assessment during a clinic visit. Stable renal transplant recipients in two clinical studies were evaluated and received immunosuppressive regimens comprised of either cyclosporine or tacrolimus with mycophenolic acid. Face, content, and construct validity were assessed to document these adverse effect evaluations. Inter-rater reliability was determined using the Kappa statistic and intra-class correlation.

Results

A total of 58 renal transplant recipients were assessed using the adverse effects scoring system confirming face validity. Nephrologists (subject matter experts) rated the 18 adverse effects as: 3.1 ± 0.75 out of 4 (maximum) regarding clinical importance to verify content validity. The adverse effects scoring system distinguished 1.75-fold increased gastrointestinal adverse effects (p = 0.008) in renal transplant recipients receiving tacrolimus and mycophenolic acid compared to the cyclosporine regimen. This finding demonstrated construct validity. Intra-class correlation was 0.81 (95% confidence interval: 0.65-0.90) and Kappa statistic of 0.68 ± 0.25 for all 18 adverse effects and verified substantial inter-rater reliability.

Conclusions

This immunosuppressive adverse effects scoring system in stable renal transplant recipients was evaluated and substantiated face, content and construct validity with inter-rater reliability. The scoring system may facilitate prospective, standardized clinical monitoring of immunosuppressive adverse drug effects in stable renal transplant recipients and improve medication adherence.

Nuclear translocation of nuclear factor of activated T cells (NFAT) as a quantitative pharmacodynamic parameter for tacrolimus

Nuclear factor of activated T cells (NFAT) is a family of transcription factors involved in regulating the immune response. The canonical NFAT pathway is calcium-dependent and upon activation, NFAT is dephosphorylated by the phosphatase, calcineurin. This results in its translocation from the cytoplasm to the nucleus and transcription of downstream target genes that include the cytokines IL-2, IL-10, and IFNγ. Calcineurin inhibitors including tacrolimus inhibit the NFAT pathway and are used as immunosuppressants in transplant settings to prevent graft rejection. There is, as yet, no direct means to monitor tacrolimus pharmacodynamics. In this study, a rapid, quantitative, image cytometry-based measurement of nuclear translocation of NFAT1 is used to evaluate NFAT activation in T cells and its tacrolimus-induced inhibition. A strong dose-dependent correlation between NFAT1 inhibition and tacrolimus dose is demonstrated in vitro. Time kinetic analysis of NFAT1 inhibition in plasma from stable renal transplant recipients before and after an in vivo dose with tacrolimus correlated with the expected pharmacokinetic profile of tacrolimus. This was further corroborated by analysis of patients' autologous CD4 and CD8 T cells. This is the first report to show that the measurement of NFAT1 activation potential by nuclear translocation can be used as a direct, sensitive, reproducible and quantitative pharmacodynamic readout for tacrolimus action. These results, and the rapid turnaround time for this assay, warrant its evaluation in a larger clinical setting to assess its role in therapeutic drug monitoring of calcineurin inhibitors.

Pharmacokinetics and Pharmacodynamic Response of Methylprednisolone in Premenopausal Renal Transplant Recipients

Chronic glucocorticoid therapy is prescribed in renal transplant recipients according to empiric dose-tapering schedules, which assume a similar pharmacologic response in men and women. The study objectives were (a) to compare the pharmacokinetics of methylprednisolone in premenopausal renal transplant recipients with previously studied male counterparts and (b) to describe the pharmacodynamic response of the hypothalamic-pituitary-adrenal axis during chronic steroid therapy. Thirteen stable premenopausal subjects (ages 30 to </=49 years) receiving chronic glucocorticoid therapy were evaluated for methylprednisolone, cortisol, and adrenocorticotropin hormone (ACTH) over 24 hours after an intravenous infusion of methylprednisolone sodium succinate. Most patients were evaluated during the luteal phase of the menstrual cycle. Pharmacokinetic parameters of methylprednisolone with cortisol and ACTH responses were determined. Results were compared to counterpart male subjects who participated in a prior study. The total clearance of methylprednisolone for the female subjects was 15.6 +/- 5.99 L/h compared to the males with 21.5 +/- 8.67 L/h (P <.05). When normalized for total or lean body weight, no significant difference was noted (P =.614). A 3-fold interpatient variation in weight-adjusted clearance was noted for female subjects. Dose-normalized methylprednisolone a AUC was greater in women (66.1 +/- 19.8 ng*h/mL) than men (46.4 +/- 19.7 ng*h/mL) (P =.174). Total cortisol AUC was not different between groups (P =.599). Despite chronic steroid therapy, 9 of 13 women had a normal cortisol profile and an ACTH AUC of 299 +/- 102 pg*h/mL. It was concluded that methylprednisolone clearance in women was significantly slower compared to men. When drug clearance was normalized for total and lean body weight, no gender difference was noted. These findings are in contrast to prior data indicating a more rapid methylprednisolone clearance in healthy women. These findings suggest that doses of glucocorticoids should be prescribed on a milligram/kilogram basis instead of empiric dosing schedules.

The MDRD equation underestimates the prevalence of CKD among blacks and overestimates the prevalence of CKD among whites compared to the CKD-EPI equation: a retrospective cohort study

BACKGROUND

Black individuals are far more likely than white individuals to develop end stage renal disease (ESRD). However, earlier stages of chronic kidney disease (CKD) have been reported to be less prevalent among blacks. This disparity remains poorly understood. The objective of this study was to evaluate whether the lower prevalence of CKD among blacks in early stages of CKD might be due in part to an inability of the MDRD equation to accurately determine early stages of CKD in both the black and white population.

METHODS

We conducted a retrospective cohort study of 97, 451 patients seen in primary care clinic in Veterans Integrated Service Network 2 (VISN 2) over a 7 year period to determine the prevalence of CKD using both the Modification of Diet in Renal Disease (MDRD) Study equation and the more recently developed CKD Epidemiology Collaboration (CKD-EPI) equation. Demographic data, comorbid conditions, prescription of medications, and laboratory data were recorded. Logistic regression and quantile regression models were used to compare the prevalence of estimated glomerular filtration rate (eGFR) categories between black and white individuals.

RESULTS

The overall prevalence of CKD was lower when the CKD-EPI equation was used. Prevalence of CKD in whites was 53.2% by MDRD and 48.4% by CKD-EPI, versus 34.1% by MDRD and 34.5% by CKD-EPI in blacks. The cumulative logistic regression and quantile regression showed that when eGFR was calculated by the EPI method, blacks were as likely to present with an eGFR value less than 60 mL/min/1.73 m2 as whites. Using the CKD-EPI equation, blacks were more likely than white individuals to have stage 3b, 4 and 5 CKD. Using the MDRD method, the prevalence in blacks was only higher than in whites for stage 4 and 5 CKD. Similar results were obtained when the analysis was confined to patients over 65 years of age.

CONCLUSIONS

The MDRD equation overestimates the prevalence of CKD among whites and underestimates the prevalence of CKD in blacks compared to the CKD-EPI equation.

CKD in MYH9-related disorders

MYH9-related disorders are rare causes of chronic kidney disease (CKD) presenting as chronic glomerulonephritis and derive from mutations of the MYH9 gene, which encodes for the nonmuscle myosin heavy chain IIA. These disorders are autosomal dominant and include May-Hegglin anomaly and Sebastian, Fechtner, and Epstein syndromes. Diagnosis of these disorders is made first in early childhood because of the characteristic peripheral-blood smear findings of thrombocytopenia, giant platelets, and variably detected basophilic cytoplasmic inclusion bodies in leukocytes. CKD typically develops later in adulthood and may progress to end-stage renal disease. MYH9-related disorders may be associated with deafness and cataract; hence, Alport syndrome becomes important in the differential diagnosis. However, the autosomal dominance pattern of inheritance and characteristic peripheral-blood smear findings in the former help differentiate the two conditions. New evidence suggests that MYH9 gene alterations also are associated with a greater risk of focal segmental glomerulosclerosis and hypertensive nephrosclerosis in African Americans. The purpose of this review is to focus on the known, but rarely recognized association of MYH9-related disorders with CKD and highlight the recent discoveries related to the MYH9 gene that may explain the reason for a high CKD burden in African Americans.

Acute renal failure during pregnancy secondary to spontaneous perirenal hematoma

A 32-year-old pregnant female presented with right flank pain, hematuria, and ARF at 25 weeks of gestation. Imaging studies demonstrated right perinephric hematoma, which compressed the inferior vena cava. ARF improved with expectant care as the hematoma gradually resolved.

Postpartum hemolytic uremic syndrome in a patient with preexisting hypertension and resolving preeclampsia

Postpartum hemolytic uremic syndrome (PHUS) is an uncommon and potentially devastating complication of pregnancy. We report a case of PHUS in a patient with chronic hypertension and preceding preeclampsia. Since early and appropriate therapy results in remission in most patients with PHUS, the sometimes subtle differences between this syndrome and preeclampsia are reviewed.

The clinical impact of 1:1 conversion from Neoral to a generic cyclosporine (Gengraf) in renal transplant recipients with stable graft function

The introduction of cyclosporine (CYA) to the immunosuppressive armamentarium has had a significant effect on graft survival. An improvement in the formulation from the oil-based to a microemulsion-based form has resulted in better absorption and more predictable CYA bioavailability. Since the introduction of the first microemulsion form (Neoral), several bioequivalent formulations are now available and are switched in a 1:1 fashion at pharmacies to curtail costs. The purpose of our study was to study the effect of a 1:1 switch from Neoral to Gengraf on CYA trough levels and serum creatinine (SRC) in renal transplant recipients with stable graft function. Eighty-two renal transplant recipients with stable graft function were enrolled in the study, and of these, 73 were switched to Gengraf, whereas nine remained on Neoral. The 13 patients switched to Gengraf required a dosage change after the mean CYA trough levels changed from 234 +/- 96 ng/mL at baseline to 289 +/- 102 ng/mL (p < 0.05) at 2 wk. With the adjustments in dosage, the levels approached the baseline trough concentrations (239 +/- 151 ng/dL). The nine patients who remained on Neoral had no change in the CYA levels or SCR. Nearly 20% of patients who switched to a bioequivalent CYA preparation required a dose adjustment to return to pre-conversion CYA trough levels. Our study raises serious concerns regarding the switchability of generic CYA for Neoral without careful follow-up therapeutic drug monitoring.

Anti-CD20 monoclonal antibody (Rituximab) for life-threatening hemolytic-uremic syndrome

Rituximab is a chimaeric monoclonal antibody directed against the CD20 antigen. It has been successfully used in B-cell malignancy and its efficacy in the treatment of in autoimmune hemolytic anemia and other autoimmune diseases is being investigated. There are also few case reports of its success in thrombotic thrombocytopenic purpura, but no reports of its use in hemolytic-uremic syndrome (HUS). We report a 36-year-old patient who had lost the function of her native kidneys secondary to HUS. After more than 1 year in clinical remission, she received a living unrelated kidney transplant. This immediately precipitated a severe relapse of HUS. The process was abrogated but not completely inactivated, despite over 40 plasma exchange treatments. Consequently, she was given Rituximab in courses of two to three doses, each dose 375 mg/m(2), at weekly intervals with remarkable stabilization of her disease for approximately 6 months.

Human immunodeficiency virus-associated nephropathy: a primary care perspective

The advent of highly active antiretroviral therapy represents a significant advance in medical care for human immunodeficiency virus (HIV)-infected persons. However, not everyone has derived the expected benefits of antiretroviral therapy and HIV-associated diseases such as nephropathy still occur in at-risk populations. Currently, there are no recommendations for screening HIV-positive patients for HIV-associated nephropathy. We propose semiannual screening for proteinuria in HIV-positive African Americans and patients with a family history of renal disease, and provide an algorithm for evaluation.

Randomized, open-label preference study of two cyclosporine capsule formulations (usp modified) in stable solid-organ transplant recipients

BACKGROUND

Prior research has indicated patient dissatisfaction with the odor, size, and taste of cyclosporine capsules, as well as the halitosis and body odor the capsules can cause.

OBJECTIVES

The purposes of this investigation were to (1) compare the overall cyclosporine capsule preference (Gengraf vs Neoral) in stable, solid-organ transplant recipients, (2) assess patient preference based on specific capsule attributes, and (3) determine the reliability of the Cyclosporine Capsule SatiSfaCtion Survey (original to this study).

METHODS

In this multicenter, randomized, open-label, parallel-group, preference study, patients were recruited from 144 centers in North America with established transplant programs. Solid-organ transplant recipients who had taken stable doses of cyclosporine (Neoral) for >/=2 consecutive months were randomized in a 9:1 ratio to receive another cyclosporine formulation (Gengraf) or to remain on Neoral therapy. Patients completed the Cyclosporine Capsule Satisfaction Survey prior to randomization (baseline survey) and after taking the study drug for 4 weeks (final survey). The survey consisted of multiple attribute items with high face validity in assessing patients' perceptions and preferences with regard to their overall experience, as well as specific attributes of cyclosporine capsules known to affect patient acceptance.

RESULTS

The intent-to-treat population included 1906 patients (1211 men, 693 women [sex unknown in 2 patients]; mean [SD] age, 50.2 [12.4] years). A total of 1708 patients were switched to Gengraf; 198 continued on Neoral. Based on their overall experience with both capsule formulations, the majority of patients switched to Gengraf (61.9%) responded that they preferred the Gengraf capsule, compared with 13.7% who preferred the Neoral capsule and 24.4% who indicated no preference (P < 0.001). A similar preference for Gengraf was observed based on capsule odor (66.3%), ease of swallowing (51.5%), taste (57.1%), and impact on breath odor (52.5%) and body odor (48.4%) (P < 0.001 for each test). The results of internal consistency and reproducibility calculations were high for the Cyclosporine Capsule Satisfaction Survey. Internal consistency ranged from alpha = 0.84 to 0.95 for the subscales and was alpha = 0.95 for the overall score. Ranges for reproducibility in the subscales were r = 0.75 to 0.79, with an overall reproducibility of r = 0.85. Guyatt's responsiveness statistics for the subscale and overall scores were moderately high to very high, indicating that the survey is capable of measuring change in response to treatment.

CONCLUSIONS

Of the transplant recipients receiving Gengraf in this study, most preferred Gengraf to Neoral based on overall experience, capsule odor, difficulty swallowing, taste, breath odor, and body odor. Among all study patients, fewer patients receiving Gengraf were bothered by capsule odor, difficulty in swallowing, taste, or the impact on breath or body odor compared with patients who continued to receive Neoral. Internal consistency, reproducibility, and responsiveness results show that the Cyclosporine Capsule Satisfaction Survey is a psychometrically valid instrument that is appropriate for use in clinical trials.

Donor calculi induced acute renal failure

Nephrolithiasis is an infrequent complication following renal transplantation and acquisition of a stone with the donor kidney is rare. Indeed only a few cases of donor stones causing renal failure have been reported. Since the grafted kidney is denervated, stone disease may not present with the classic renal colic but rather with acute renal failure secondary to the obstruction. Identification of the precise cause is critical in order to avoid inappropriate therapy. We present our experience of two renal transplant patients who developed obstructive uropathy by stones originating from the donor kidneys.

Thromboxane receptors in human kidney tissues

Thromboxane (TX) A2 effects in the kidneys include contraction of glomerular mesangial cells and intrarenal vascular tissue. A kidney cDNA encoding a TX receptor expressed in rat renal glomeruli and rat renal arterial smooth muscle cells has been reported. However, TXA2 receptors in human kidneys have not been documented. The purpose of this study was to identify and characterize TXA2 receptors in glomeruli and intrarenal arteries isolated from human kidneys. Normal kidneys, not used for transplant because of technical reasons, were kept at -70 degrees C and used for research purposes. The glomeruli and intrarenal arteries were isolated from renal cortical tissue by a mechanical sieving technique. The equilibrium dissociation constant and receptor number were determined by nonlinear analysis of binding inhibition data. The data were generated in radioreceptor assays using [125I]-BOP, a stable analog of TXA2. The dissociation constants (mean +/- SEM) for binding of I-BOP to human glomeruli and intrarenal arterial membranes were 6.6 +/- 1.1 nM (n = 7) and 20 +/- 6 nM (n = 7), respectively (p < 0.05). The receptor number was 311 +/- 91 fmol/mg protein (n = 7) in glomeruli and 74 +/- 16 fmol/mg protein (n = 7) in intrarenal arterial membranes (p < 0.04). The order of specificity of TXA2 analogs for [125I]-BOP binding sites was similar in glomeruli and in arterial membranes and was I-BOP > or = U46619 > or = pinane TXA2 > or = carbocyclic TXA2 > or = PGH2. These findings provide direct evidence for the presence of specific, high-affinity [125I]-BOP binding sites in human renal glomeruli and extraglomerular vascular tissue. These data also indicate that the human binding sites have higher affinity for the TXA2 agonist I-BOP than for PGH2.

Hemodynamic and renal effects of U-46619, a TXA2/PGH2 analog, in late-pregnant rats

The vasoconstrictor effects of pressor agents are attenuated during pregnancy. Thromboxane A2 (TXA2) is produced in great quantities during hypertension in pregnancy, and therefore it is important to know whether pregnancy modifies the pressor effects of TXA2. The TXA2 analog U-46619 was infused in anesthetized, acutely prepared and conscious, chronically prepared late-pregnant and nonpregnant female rats to examine its systemic hemodynamic and renal effects. Mean arterial pressure (MAP) and total peripheral resistance (TPR) were lower in anesthetized pregnant than nonpregnant rats (P < 0.01). The infusion of U-46619 into the aortic arch resulted in elevation of MAP only in pregnant rats, due to a greater elevation of TPR (60 +/- 17%) compared with nonpregnant rats (36 +/- 6%, P < 0.05). The pressor effect of intravenously infused U-46619 was also enhanced in conscious pregnant versus nonpregnant rats, and the increase in renal vascular resistance was undiminished. U-46619 increased hematocrit and plasma protein concentration more during pregnancy, which suggested greater reduction of plasma volume. The urinary excretion of sodium (-1.49 +/- 0.25 vs. -0.54 +/- 0.24 micromol/min) and water was reduced more in pregnant than nonpregnant rats during U-46619 (P < 0.01). Thus the MAP and renal effects of the TXA2 analog are exaggerated during pregnancy in the rat.

CD4+ and CD8+ lymphocyte and cortisol response patterns in elderly and young males after methylprednisolone exposure

The elderly have impaired cellular immunity and are more predisposed to opportunistic infections after long term glucocorticoid treatment. No data, examining the response of lymphocyte subsets (CD4+, CD8+) under baseline conditions and after exposure to methylprednisolone in young and elderly males, are available. This crossover study examined lymphocyte subsets and cortisol response patterns in seven elderly males (66-82 years) and five young males (24-37 years) randomized into Phase I (24 hr baseline) and Phase II (10 mg intravenous dose of methylprednisolone). Whole blood samples were obtained at 0, 4, 8, 12 and 24 hr to determine total lymphocytes and CD4+ and CD8+ cells utilizing monoclonal antibodies and flow cytometry. The absolute number of lymphocyte subsets and the lymphocyte area under the time curve (AUC) were measured and a 12 and 24 hr lymphocyte response ratio (AUC Phase II divided by AUC Phase I) was determined. Serial plasma samples over 24 hours were collected to quantitate cortisol (Phase I) and methylprednisolone concurrent with cortisol (Phase II). Pharmacokinetic parameters were generated and the cortisol AUC was determined. The AUC values for lymphocytes and cortisol from Phase II quantitated the pharmacologic response to methylprednisolone exposure while Phase I data described the interpatient variability in these parameters. Diurnal patterns for lymphocytes and cortisol were noted in all subjects during Phase I. The mean CD4+ and CD8+ lymphocyte AUC from 0 to 24 hr during Phase I was significantly smaller for the elderly when compared to young men. However, after exposure to methylprednisolone, lymphopenia occurred in all subjects with a mean decline of 54% in the elderly and 60% (p = 0.44) in young subjects for the total lymphocyte count and returned to baseline by 8-12 hr. During Phase II, the CD4+ lymphocytes (72% decline in elderly; 70% in young; p = 0.71) demonstrated a more notable decline than CD8+ cells (44% decline in elderly; 52% in young; p = 0.31) with a nadir occurring between 4 to 6 hr for both subsets. The lymphocyte response ratio was not significantly different between groups for total, CD4+, and CD8+ cells at 12 hr or 24 hr determinations. A slower clearance of methylprednisolone was noted in the elderly (mean: 256 mL/hr/Kg) than in the young men (mean: 359 mL/hr/Kg; p < 0.05) during Phase II with no significant difference found between groups for volume of distribution, elimination rate constant or half-life. A significantly smaller cortisol suppression ratio [0.36+/-0.11 (elderly) versus 0.58+/-0.11 (young), p = 0.01] which indicates a more profound cortisol suppression was noted. A significant correlation of -0.61 (p < 0.05) between drug exposure (methylprednisolone AUC) and pharmacologic effect (cortisol suppression ratio) was noted for the combined data in the young and elderly males. During Phase I, the CD4+ and CD8+ lymphocyte AUC was significantly smaller in the elderly. A definite suppression pattern for total, CD4+ and CD8+ lymphocytes and cortisol was noted after methylprednisolone exposure in young and elderly males. An age-dependent suppression of cortisol during Phase II was noted but the degree of lymphopenia after drug exposure did not differ between the young and elderly group for any of the cell subsets. These data from healthy elderly provide a basis for further studies to assess immunologic and endocrinologic responses among elderly patients requiring chronic glucocorticoid therapy.

Cortisol pharmacodynamics after methylprednisolone administration in young and elderly males

Glucocorticoids are commonly prescribed in the elderly on an empiric basis with little consideration for the age-related alterations in pharmacologic response. The objectives of this study were to compare the effect of methylprednisolone on cortisol patterns in elderly and young healthy men, to define the relationship between pharmacokinetic parameters of methylprednisolone and pharmacodynamics of cortisol in the elderly and young men. Seven healthy, elderly males (69-82 years old) and five healthy, young males (24-37 years old) participated in a 24-hour pharmacodynamic trial with randomized assignment to a control period (Phase 1) and a methylprednisolone period (Phase II). Serial blood samples were obtained throughout both study periods. Cortisol measurements included the total area under the concentration-time curve (AUC), return AUC, and suppression ratio. During Phase I, a circadian pattern was noted in both groups. After exposure to methylprednisolone (Phase II), a linear decline in serum concentrations of cortisol was observed in both groups. The return AUC of cortisol (425 +/- 357 ng.hr/mL [elderly] versus 854 +/- 216 ng.mL [young]) and the total AUC 764 +/- 340 ng.h/mL [elderly] versus 1,230 +/- 258 ng.hr/mL [young]) were significantly lower in the older men. In addition, a significant decline in total AUC and nadir concentration of cortisol from Phase I to Phase II was noted within both groups. The suppression ratio was significantly greater in the elderly men (mean, 0.38 versus 0.58 in young), which indicates a greater degree of adrenal suppression after administration of methylprednisolone. Exposure to methylprednisolone, as measured by AUC, was 554 +/- 215 ng.hr/kg (elderly) and 389 +/- 102 ng.hr/kg (young). The greater exposure to methylprednisolone noted in the elderly yielded significant combined correlations for both groups with AUC, return AUC, and suppression ratio of cortisol. A more significant response of cortisol to the exogenous glucocorticoid was apparent in the elderly men. In addition, a slower clearance of methylprednisolone was noted in the elderly group compared with their young counterparts. The effect of reduced clearance of methylprednisolone on the suppression ratio indicates the interrelationship between the disposition of a single dose of an exogenous glucocorticoid and response patterns of cortisol.

Methylprednisolone and cortisol metabolism during the early post-renal transplant period

Despite the widespread use of methylprednisolone and the well-appreciated effects of this drug on HPA suppression, little data is available which describes individual patient exposure to both methylprednisolone and cortisol following renal allograft placement. The clinical utilization of methylprednisolone during the early post-transplant period is based upon standardized dosing protocols that do not consider factors which may influence the pharmacokinetics of this drug during the post-transplant period. Therefore, this study was designed to examine the pharmacokinetics of methylprednisolone (mean dose: 28 mg) and cortisol pharmacodynamics in 9 renal transplant recipients (4 females; 5 males) who were studied during the early post-transplant period (5 to 12 days after surgery). All patients (mean serum creatinine: 1.4 +/- 0.3 mg/dl) had serial blood samples collected over a 12- to 24-hour period (depending upon the dosing schedule) which were analyzed concurrently for methylprednisolone and cortisol. A three-fold variation in drug clearance ranging from 174 to 638 ml/h/kg with a range in the volume of distribution of 0.83 to 2.24 l/kg and resultant half-lives ranging from 1.20 to 3.02 hours was noted. The cortisol response was quantitated by a 12-hour cortisol area under the curve (C-AUC12) to examine the interpatient cortisol patterns during the early post-transplant period. C-AUC12 ranged from 44.0 to 636 ng.h/ml. Significant correlations were noted between the cortisol plasma concentration at 12 hours and methylprednisolone clearance and area under the concentration versus time curve (AUC). Interpatient variability in the disposition of methylprednisolone and cortisol response noted during the early post-transplant period contradict the clinical assumptions which underlie the fixed dosing protocols currently utilized for methylprednisolone.

Pregnancy enhances the pressor response to thromboxane analogues in rabbits

In this study, we first tested the hypothesis that the previously demonstrated circulatory failure and thrombocytopenia induced by intracaval administration of thromboxane A2 (TxA2) analogues in nonpregnant (NP) rabbits [G. Losonczy, I. Mucha, J. DiPirro, J. Sweeney, G. Brown, J. Brentjens, and R. Venuto. Am. J. Physiol. 265 (Regulatory Integrative Comp. Physiol. 34): R772-R780, 1993] could be avoided if the compounds were given instead into the aortic arch. Conscious New Zealand White rabbits received bolus injections of U-46619 (5-20 micrograms) through a previously implanted catheter threaded into the aortic arch. Indeed, mean arterial pressure (MAP) rose modestly, and thrombocytopenia did not develop. Next, we compared the blood pressure responses of pregnant (P) rabbits with those of NP rabbits to intra-aortic U-46619 and I-BOP, because they had been found to be resistant to both the hypotensive and platelet aggregatory effects of intracaval U-46619. Resting blood pressure was lower in P than in NP rabbits (74 +/- 3 vs. 95 +/- 2 mmHg), but showed a greater increase in response to U-46619. For example, following a 20-micrograms dose blood pressure rose 20 +/- 0.3 mmHg in P vs. 12 +/- 2.1 mmHg in NP rabbits (P < 0.02). Similar results were obtained with the second TxA2 analogue I-BOP. Pregnancy-induced enhancement of blood pressure elevation may be the consequence of peripheral vasoconstriction, which was not seen in NP rabbits. Thus the actions of TxA2 analogues U-46619 and I-BOP are markedly influenced by the route of administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Post-transplant diabetes mellitus and methylprednisolone pharmacokinetics in African-American and Caucasian renal transplant recipients

Post-transplant diabetes among renal transplant recipients is more prevalent in the African-American population. However, it is unknown if methylprednisolone (a commonly prescribed glucocorticoid in transplant patients) pharmacokinetics is altered among African-American renal allograft recipients compared to Caucasian counterparts. Therefore, the objectives of this study were to identify the occurrence of post-transplant diabetes in our clinic population and to characterize the pharmacokinetics of methylprednisolone among our African-American and Caucasian renal transplant recipients. A retrospective chart survey was done on African-American and Caucasian recipients with stable renal function and no history of diabetes pre-transplantation in order to characterize the occurrence of post-transplant diabetes in our clinical population. The survey was conducted from January 1985 to January 1992 in recipients with graft survival of at least 3 months. Post-transplant diabetes was defined as two fasting glucose serum concentrations greater than 140 mg/dl or one random serum glucose concentration greater than 200 mg/dl which was confirmed by a fasting serum glucose value greater than 140 mg/dl and a 2 hour post-prandial greater than 200 mg/dl. A 24-hour pharmacokinetic evaluation was conducted in a sub-group of African-American and Caucasian patients after intravenous administration of methylprednisolone. Over the survey period, 75 renal transplants (30 females; 45 males) were performed and 50 of these transplant recipients (24 females; 26 males) were not diabetic prior to the allograft placement. Of these 50 patients, 22 males and 17 females fulfilled the inclusion criteria established for the retrospective survey.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics of methylprednisolone during acute renal allograft rejection

High dose methylprednisolone is administered empirically by fixed daily boluses to renal transplant recipients who are experiencing acute rejection episodes. Little information is available characterizing the pharmacokinetics of high-dose methylprednisolone in these individuals, who are often acutely ill. Therefore, 5 renal transplant recipients (2 men; 3 women) were studied during an acute rejection episode (mean serum creatinine = 2.6 +/- 0.7 mg/dl) which occurred within the first 8 months post-transplantation. The rejection episode was characterized clinically by at least two of the following: fever, leukocytosis, graft tenderness and an increase in serum creatinine. All patients received bolus doses of methylprednisolone for 3 consecutive days during the rejection episode. All patients were studied on the 3rd day of bolus dosing and received 250 mg methylprednisolone by an i.v. infusion. In phase II, 4 patients were studied during a period of stable renal function when the methylprednisolone was given at lower chronic immunosuppressive doses. Serum samples were taken prior to infusion and serially over the following 24 hours. The serum samples were analyzed for methylprednisolone with high-performance liquid chromatography (HPLC) and pharmacokinetic parametes were generated. During rejection episodes, the methylprednisolone clearance values were 523 +/- 154 ml/h/kg with a corresponding mean volume of distribution of 1.89 +/- 0.72 l/kg. The mean methylprednisolone half-life was 2.61 +/- 0.62 h. During Phase II, the methylprednisolone clearance was 358 +/- 95 ml/h/kg with a half-life of 3.05 h. This observation indicates that methylprednisolone metabolism is increased during acute rejection compared to that seen during chronic immunosuppressive dosing with this agent.

Methylprednisolone pharmacokinetics, cortisol response, and adverse effects in black and white renal transplant recipients

It is generally assumed that chronic glucocorticoid therapy is similar pharmacologically when administered to either black or white renal transplant recipients, resulting in adrenal suppression, low circulating plasma cortisol concentrations, and a similar degree of drug exposure and toxicity. To examine this theory and to investigate the relationship of glucocorticoid metabolism to steroid-induced adverse effects among specific ethnic groups of renal transplant recipients, 9 black and 9 white male patients chronically receiving methylprednisolone were enrolled. All patients had stable renal function and were matched for age, weight, and time since transplant. Standard pharmacokinetic parameters for methylprednisolone were determined and cortisol responses were characterized by total cortisol area under the concentration curve (AUC), return cortisol AUC, and cortisol suppression half-life. All patients received their daily oral dose of methylprednisolone (mean daily dose = 11 mg for blacks and 11 mg for whites) as an intravenous infusion with serial plasma samples obtained over 24 h. The patients were assessed for the presence of specific cushingoid manifestations (buffalo hump, moon facies) and steroid-associated diabetes. Methylprednisolone and cortisol were analyzed via HPLC. In the black patients, the mean clearance of methylprednisolone (206 +/- 70 ml/hr/kg) was significantly slower with a smaller volume of distribution (0.95 +/- 0.32 L/kg) when compared with the white group (327 +/- 129 ml/hr/kg, P = 0.03; volume of distribution = 1.33 +/- 0.27 L/kg, P = 0.015). Despite chronic methylprednisolone therapy, a definite 24-hr cortisol response pattern was noted in 15 of the 18 patients with a mean total cortisol AUC of 732 +/- 443 ng.hr/ml in blacks and 539 +/- 361 ng.hr/ml in whites (P = 0.17, black vs. white). The mean cortisol suppression half-life was 4.31 +/- 1.54 hr in black recipients and 4.11 +/- 1.49 hr in whites (P = 0.48). The mean return cortisol AUC for the black patients was 327 +/- 279 ng.hr/ml and 370 +/- 207 ng.hr/ml for white patients (P = 0.28). The serum cortisol nadir for black patients was 12.3 +/- 7.2 ng/ml, which was significantly higher than the cortisol nadir in white patients (6.4 +/- 4.4 ng/ml; P = 0.03). A majority (94%) of patients (9 black, 8 white) had moon facies and 27% of patients (3 black, 1 white) had a buffalo hump. While 5 of 9 black patients had steroid-associated diabetes, no white patients manifested this adverse effect. The black patients with diabetes had higher cortisol AUCs with lower methylprednisolone clearances than the white group.(ABSTRACT TRUNCATED AT 400 WORDS)

Repeated assessment of methylprednisolone pharmacokinetics during chronic immunosuppression in renal transplant recipients

OBJECTIVE

To compare the pharmacokinetics of methylprednisolone in renal transplant recipients on 2 occasions separated by at least 1 month during chronic immunosuppression.

DESIGN

A prospective unblinded trial.

PATIENTS

Ten renal transplant recipients (aged 25-62 years) evaluated in a public university-affiliated hospital clinic.

INTERVENTIONS

All patients received their chronic oral dose of methylprednisolone as a 10-20-minute intravenous infusion during the 2 study periods.

MAIN OUTCOME MEASURES

Serum methylprednisolone concentrations were determined by HPLC and were used to generate the pharmacokinetic parameters of the drug.

RESULTS

During study 1, which ranged from 1.2 to 24 months posttransplant, the mean +/- SD methylprednisolone dose was 13.2 +/- 6.4 mg. In study 2 (2.5-38.5 mo posttransplant), the mean dose was 10.6 +/- 3 mg. During both study periods, methylprednisolone concentrations exhibited a monoexponential decline. Considerable variability in methylprednisolone clearance was observed between periods in certain patients. Four of the 10 patients demonstrated a reduction in clearance from study 1 to study 2, which ranged from a 28% to a 53% decrease. Two patients exhibited an increase in clearance of 40% and 49%. The mean +/- SD total body clearance in study 1 was 363 +/- 330 mL/min/kg, whereas the mean volume of distribution was 1.18 +/- 0.53 L/kg. The mean elimination rate constant was 0.29 +/- 0.14 h-1, with a mean serum half-life of 2.87 +/- 1.15 h during the first phase. In study 2, the mean methylprednisolone clearance was 261 +/- 150 mL/min/kg (p > 0.05) and the mean volume of distribution was 0.89 +/- 0.31 L/kg (p > 0.05). The mean serum half-life of methylprednisolone was 2.91 +/- 0.60 h (p > 0.05), with the mean elimination rate constant of 0.25 +/- 0.06 h-1 (p > 0.05).

CONCLUSIONS

These data demonstrate that intrapatient variability in methylprednisolone clearance exists among certain renal allograft recipients. As a result of the observed variability, patients who are continued on the same dose of methylprednisolone during the posttransplant period of chronic immunosuppression will be subjected to a changing pattern of exogenous glucocorticoid exposure. The impact of these changing patterns requires further prospective evaluation.

A proposed method for the noninvasive evaluation of renal asymmetry in a living-related donor candidate

This report proposes an adjunctive technique for the evaluation of asymmetry of renal size and function of undetermined etiology, discovered during the assessment of two living-related donor candidates. The method utilizes the observation of renal functional reserve measurement as demonstrated by oral protein loading in patients with normal and diseased kidneys. Renal function was measured as timed Ccr and estimation of differential GFR by technetium-99m diethylenetriaminepentaacetic acid (99mTcDTPA) scintigraphy. A comparison of renal function before and after protein loading in two such patients demonstrated the anticipated increase in GFR. No change in differential GFR as determined by renal scan in one patient was interpreted as supportive evidence for bilaterally normal parenchymal function. Follow-up of both donors shows continued normal renal function.

Pharmacokinetics of methylprednisolone in elderly and young healthy males

OBJECTIVE

To characterize and compare the pharmacokinetics of a single intravenous dose of methylprednisolone in elderly and young healthy males.

DESIGN

A randomized, parallel pharmacokinetic trial.

SETTING

A public university-affiliated hospital.

SUBJECTS

Seven healthy, elderly white males (aged 69 to 82 years) and five healthy, young white males (aged 24 to 37 years) who gave informed consent and fulfilled all screening criteria.

MEASUREMENTS

Serial blood samples were obtained over a 24-hour study period after intravenous administration of a 10-mg dose of methylprednisolone. Serum methylprednisolone concentrations were determined by high performance liquid chromatography and utilized to determine the pharmacokinetic parameters.

RESULTS

Methylprednisolone serum concentrations declined in a linear manner in both groups. However, 4 hours after the dose, the mean serum concentration of methylprednisolone was 50.9 +/- 15.1 ng/mL in the elderly group and 37.6 +/- 7.5 (P = 0.07) ng/mL in the young group. The clearance of methylprednisolone was 237 +/- 62 mL/h/kg, with a volume of distribution of 1.10 +/- 0.07 L/kg, for the elderly group, whereas the young males had a mean drug clearance of 359 +/- 90 mL/h/kg (P < 0.05) and a mean volume of distribution of 1.28 +/- 0.34 L/kg. The half-life of methylprednisolone ranged from 1.90 to 5.40 hours in the elderly group; the range was 1.99 to 3.31 hour (P = 0.016) in the young group.

CONCLUSION

A slower methylprednisolone clearance was noted in the elderly group compared with the young counterparts. This pharmacokinetic alteration seen in healthy elderly subjects may contribute to the increased incidence of adverse effects from chronic glucocorticoid therapy that has been observed among elderly patients.

The cytomegalovirus-antigenemia assay in the diagnosis of posttransplant cytomegalovirus infection

Cytomegalovirus (CMV) infection continues to be a major cause of morbidity and mortality in transplant recipients, yet prompt diagnosis remains a problem. A new assay has been developed that detects CMV antigens in peripheral blood leukocytes (CMV-AG). A retrospective analysis of the experience with this assay was performed, and its usefulness in the diagnosis of CMV infection in renal transplant recipients with unexplained fever was compared with that of conventional modalities (buffy coat culture, detection of circulating anti-CMV immunoglobulin M). The results suggest that the CMV-AG assay is a more rapid and sensitive test than existing modalities in the early diagnosis of CMV infection. When expressed quantitatively, it can discriminate between CMV infection and CMV disease, and it is useful in monitoring the course of infection and the response to therapy.

Cortisol pharmacodynamic response to long-term methylprednisolone in renal transplant recipients

STUDY OBJECTIVE

To examine the pharmacodynamic patterns of cortisol and pharmacokinetic values of long-term methylprednisolone in renal transplant recipients.

DESIGN

Twenty-four-hour pharmacokinetic and pharmacodynamic evaluation of patients who participated in a glucocorticoid-monitoring program.

SETTING

University-based renal transplant clinic.

PATIENTS

Fourteen renal transplant recipients studied during a clinically stable period.

INTERVENTIONS

The daily oral methylprednisolone dose for each patient was administered intravenously, and serial plasma cortisol and methylprednisolone samples were obtained over 24 hours.

MEASUREMENTS AND MAIN RESULTS

Methylprednisolone was analyzed by high-performance liquid chromatography. The baseline morning cortisol serum concentrations ranged from 9.8-210.7 ng/ml. After the drug was administered, cortisol declined in a linear fashion with a mean suppression half-life of 2.4 +/- 0.9 hours. The cortisol nadir was reached at 12-16 hours in 11 of 14 patients. The return cortisol area under the curve (AUC-Cret) was noted in all patients and ranged from 57-987 ng.hr/ml. The total cortisol area under the curve was greater in patients who had been transplanted for longer than 2 years (1676 +/- 252 vs 836 +/- 405 ng.hr/ml; p < 0.05) compared with more recently transplanted patients. Methylprednisolone clearance ranged from 100-1181 ml/hr/kg with a mean volume of distribution of 1.3 +/- 0.6 L/kg. The methylprednisolone half-life ranged from 1.2-4.7 hours. The correlation between AUC-Cret and methylprednisolone AUC was -0.64 (p < 0.05).

CONCLUSIONS

The pharmacodynamic response of cortisol in renal transplant recipients may be associated in part with long-term steroid exposure. However, the interrelationship between the endocrine and immune system may also affect cortisol's disposition and subsequent recovery patterns in this population. Considerable interpatient variability was apparent in both the cortisol pharmacodynamic response as well as the pharmacokinetics of methylprednisolone. These findings suggest a more individualized dosing method may be necessary to optimize the immunosuppressive effect of glucocorticoids and minimize clinical toxicity.

Racial differences in the pharmacokinetics of methylprednisolone in black and white renal transplant recipients

STUDY OBJECTIVE

To examine the comparative pharmacokinetics of long-term methylprednisolone therapy in black and white renal transplant recipients.

DESIGN

Comprehensive pharmacokinetic evaluations of patients who participated in our glucocorticoid-monitoring program.

SETTING

University-based renal transplantation clinic.

PATIENTS

Six white renal transplant recipients with stable renal function, sex- and (approximate) age-matched with six preselected black patients.

INTERVENTIONS

The daily oral methylprednisolone dose for each patient was administered intravenously, and serial plasma samples were obtained over 24 hours.

MEASUREMENTS AND MAIN RESULTS

Methylprednisolone was analyzed by high-performance liquid chromatography. The drug's pharmacokinetics in black and white patients, respectively, were as follows: mean clearance 234 +/- 124 and 472 +/- 180 ml/hr/kg (p < 0.05); volume of distribution 0.3-2.0 and 0.8-2.0 L/kg; and elimination rate constant 0.13-0.41 and 0.27-0.42 hour-1 (p < 0.06). No statistical difference was noted in the last two parameters. The mean half-life of 3.4 +/- 1.4 hours in black patients compared with 2.1 +/- 0.3 hours in white patients approached statistical significance (p < 0.08).

CONCLUSIONS

These preliminary observations suggest that the disposition of methylprednisolone differs between black and white renal transplant recipients. The current method of prescribing glucocorticoids employs a fixed-dose regimen that does not take these possible interracial differences into consideration. Incorporating the differences may allow for more individualized dosing and more efficacious use of the agent in this patient population.

Comparative methylprednisolone pharmacokinetics in renal transplant patients receiving double- or triple-drug immunosuppression

OBJECTIVE

To assess the pharmacokinetics of chronic methylprednisolone therapy in renal transplant patients receiving double-drug (methylprednisolone and azathioprine) and triple-drug (methylprednisolone, azathioprine, and cyclosporine) immunosuppression.

DESIGN

Parallel, randomized trial.

PATIENTS

Fourteen renal transplant recipients (aged 29-65 y) evaluated in a public, university-affiliated hospital clinic.

INTERVENTIONS

All patients received their chronic oral dose of methylprednisolone via a 10-20-minute intravenous infusion.

MAIN OUTCOME MEASURES

Serum methylprednisolone concentrations were determined by HPLC and were used to generate pharmacokinetic parameters for this drug.

RESULTS

The mean daily methylprednisolone dosage was 19 +/- 19 mg in the double-drug group and 9 +/- 2 mg in the triple-drug group. Mean serum creatinine concentrations were 124 +/- 44 and 124 +/- 27 mumol/L, respectively. Mean methylprednisolone clearances were similar in both groups: 405 +/- 205 (double-drug) and 373 +/- 365 mL/h/kg (triple-drug) (p > 0.05). Mean steady-state volume of distribution was 1.5 +/- 0.8 L/kg in the double-drug group and 1.3 +/- 0.8 L/kg in the triple-drug group (p > 0.05). Plasma half-life ranged from 1.7 to 4.3 h (mean 2.7) in the double-drug group versus 1.4 to 3.4 h (mean 2.6) in the triple-drug group (p > 0.05).

CONCLUSIONS

These data indicate that cyclosporine had no definitive influence on methylprednisolone disposition. The results reveal a wide variation in methylprednisolone metabolism in renal transplant recipients receiving either a double- or triple-drug immunosuppressive regimen. Typically, methylprednisolone is prescribed according to a standardized dosing protocol that assumes minimal interpatient variation. Therefore, the pharmacokinetic variability noted in this study may have important clinical implications regarding the development of chronic toxicity (e.g., osteoporosis, hypothalamic-pituitary-adrenal suppression) and the attainment of successful immunosuppression.

Increased peripheral resistance during reduced uterine perfusion pressure hypertension in pregnant rabbits

The role of an increase in total peripheral resistance (TPR) and the contribution of angiotensin II (ANG II) to the hypertension induced by reduced uterine perfusion pressure (RUPP) was explored in pregnant rabbits. On the 22nd day of gestation, a catheter and a microthermocouple were placed in the aorta to measure mean arterial pressure (MAP) and cardiac output (CO), respectively. Three days later, RUPP was induced by a clip on the aorta proximal to the ovarian and distal to the renal arteries. Mean arterial pressure distal to the clip (uterine perfusion pressure) was reduced to 56 +/- 8% (mean +/- SD) of the initial level. Twenty-four hours later, MAP rose from 65 +/- 3 to 84 +/- 11 mm Hg; CO index decreased from 207 +/- 18 to 169 +/- 27 ml/min/kg; and TPR index increased from 0.32 +/- 0.03 to 0.51 +/- 0.08 mm Hg kg/ml/min, respectively (n = 7, all p less than 0.01). Sham-operated pregnant rabbits (n = 7) and non-P rabbits (n = 5) with a comparable distal aortic pressure reduction experienced no change in MAP or CO. Infusion of a receptor antagonist of angiotensin II (Sar1,Ile8-Ang II, 1 microgram/kg/min for 20 min) decreased MAP in sham-operated pregnant rabbits from 64 +/- 6 to 54 +/- 6 mm Hg (p less than 0.01) but did not change MAP in RUPP hypertensive rabbits (86 +/- 9 mm Hg before and 87 +/- 8 at the end of infusion, n = 6). These data indicate that RUPP in pregnant rabbits leads to a high resistance form of hypertension in which the formation of Ang II is not increased.

Renal blood flow response to angiotensin II infusions in conscious pregnant rabbits

Renal blood flow (RBF) was measured in conscious rabbits while nonpregnant and during pregnancy using chronically implanted ultrasonic transit-time flow probes. The effects of the cyclooxygenase inhibitor meclofenamate (5 mg/kg) and the angiotensin-converting-enzyme inhibitor captopril (5 mg/kg) on basal RBF and on RBF responses to systemic angiotensin II infusions (2.5-80 ng.kg-1.min-1) were determined. Basal RBF declined (P less than 0.001 to P less than 0.005) with meclofenamate by 9-16% in pregnant (n = 7) and by 10% in nonpregnant (n = 7) rabbits. Captopril increased (P less than 0.05 to P less than 0.01) RBF by 9-11% in pregnant (n = 5) and by 12% in nonpregnant (n = 5) rabbits. There was no effect of the vehicle (normal saline) on RBF. The reduction in RBF (% from baseline) in response to infused angiotensin II was attenuated in pregnant compared with nonpregnant rabbits. Pretreatment with meclofenamate enhanced the renal vasoconstrictor action of angiotensin II in a similar fashion in both pregnant and nonpregnant rabbits. Captopril or saline did not alter the RBF responses to angiotensin II infusions. Mean arterial pressure was lower in pregnant (78 +/- 3 mmHg, n = 7) vs. nonpregnant (88 +/- 5 mmHg, n = 10) rabbits, suggesting lower total peripheral resistance. The data indicate 1) chronically implanted ultrasonic flow probes can be an effective tool for monitoring RBF in conscious rabbits, 2) prostaglandins and the renin-angiotensin system influence basal RBF in conscious rabbits, and 3) the renal vasoconstrictor effect of angiotensin II is blunted in pregnant rabbits and this attenuated response appears to be independent of prostaglandins.