Pharmacometabolomic Assessments of Atenolol and Hydrochlorothiazide Treatment Reveal Novel Drug Response Phenotypes

Achieving hypertension (HTN) control and mitigating the adverse health effects associated with HTN continues to be a global challenge. Some individuals respond poorly to current HTN therapies, and mechanisms for response variation remain poorly understood. We used a nontargeted metabolomics approach (gas chromatography time-of-flight/mass spectrometry gas chromatography time-of-flight/mass spectrometry) measuring 489 metabolites to characterize metabolite signatures associated with treatment response to anti-HTN drugs, atenolol (ATEN), and hydrochlorothiazide (HCTZ), in white and black participants with uncomplicated HTN enrolled in the Pharmacogenomic Evaluation of Antihypertensive Responses study. Metabolite profiles were significantly different between races, and metabolite responses associated with home diastolic blood pressure (HDBP) response were identified. Metabolite pathway analyses identified gluconeogenesis, plasmalogen synthesis, and tryptophan metabolism increases in white participants treated with HCTZ (P < 0.05). Furthermore, we developed predictive models from metabolite signatures of HDBP treatment response (P < 1 × 10(-5)). As part of a quantitative systems pharmacology approach, the metabolites identified herein may serve as biomarkers for improving treatment decisions and elucidating mechanisms driving HTN treatment responses.

Abstract P4-01-09: 18F-FLT-PET/CT for the prediction of response to ANG-1005 therapy in patients with brain metastases from breast cancer

Background: ANG1005 (formerly called GRN1005) is a peptide-drug conjugate being developed for targeted treatment of brain metastases. It consists of 3 molecules of paclitaxel covalently linked to Angiopep-2 designed to cross the blood brain barrier (BBB) via the low density lipoprotein (LDL) receptor-related protein-1 (LRP1)-mediated trancytosis. This drug was evaluated in a multi-center, open-label single-arm study (GRABMB study). An interim analysis determined that the agent met the futility endpoint based on MRI assessment (SABC 2012). However, centrally confirmed responses were achieved in the study, and a biomarker substudy enrolling patients (pts) to evaluate the utility of FLT-PET in assessing response to treatment with ANG1005 suggested sufficient activity of the agent to allow continuation of the study. 18F-FLT (3’-Fluoro-3’ deoxythymidine)-PET imaging is a novel imaging modality which provides a tool for measuring in vivo tumor cell proliferation. FLT is an analog of thymidine; cellular retention of FLT reflects DNA synthesis.

Methods: Adult pts with measurable BMBC were eligible with or without history of prior WBRT. We compared 18F-FLT-PET/CT with MRI-gadolinium contrast images for brain metastases detection and for assessment of whether treatment with ANG1005 was associated with significant change in intracranial tumor uptake of 18F-FLT.

ANG1005 therapy was administered intravenously at 550 mg/m2 q 21d until progression of intra-cranial disease or unacceptable toxicity. All pts underwent 18F-FLT PET/CT imaging before and after 1 cycle of therapy with ANG1005. Pts were scanned dynamically over 30 min followed by a static whole body PET image at 1 hour post-injection. We calculated the% of change before and after therapy, with change &gt; 20% considered significant.

Results: 5/10 planned pts have been accrued to the substudy to date, and 12 metastatic brain lesions have been analyzed. The maximum standard uptake value (SUVmax) ranged from 0.8 to 4.0, mean 1.8 for baseline scans. Tumor to normal brain background ratios ranged from 3.2 to 22.3, mean 9.4. 7/12 lesions showed &gt;20% change between pre and post therapy. The average% change was (-) 42.39% ± 12.77, range: 29.2 to 66.8% (using SUVmax), and (-) 38.7% ± 14.3, range: 20.12 to 57.10% (using tumor to normal ratios). Based on brain MRI evaluation per RECIST 1.1 criteria, 1 pt had intra-cranial partial response (PR) and 3 patients had stable disease (SD). These pts remained on therapy for an average of 7 cycles, range: 5 to 9 cycles. 1 pt withdrew consent after 2 cycles of therapy and opted to receive whole brain radiation therapy. 5/42 pts achieved a confirmed investigator-assessed PR by MRI at 550 mg/m2, and 4/13 pts achieved a PR at 650 mg/m2, a dose not progressed due to toxicity.

Conclusion: This pilot study using 18F-FLT-PET imaging of brain metastases suggests that it is a promising tool for detection and measurement of CNS disease. Given that contrast-enhanced MRI detection of brain metastases represent gadolinium leakage through the BBB rather than actual tumor volume measurements, better approaches are needed to assess efficacy of therapies. Accrual to this study is ongoing. Updated results with ANG1005 will be presented during the meeting.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P4-01-09.

Low-dose electron beam radiation and romidepsin therapy for symptomatic cutaneous T-cell lymphoma lesions

BACKGROUND

Romidepsin is a structurally unique histone deacetylase inhibitor approved by the U.S. Food and Drug Administration for therapy of relapsed or refractory cutaneous T-cell lymphoma (CTCL). Localized electron beam radiation therapy (LEBT) is standard practice in the care of patients with chronically traumatized and painful lesions. Combination therapy of those two modalities may be beneficial for the therapy of CTCL.

OBJECTIVES

To report observations on supportive LEBT utilized for isolated refractory lesions in patients on romidepsin.

METHODS

Observations were made during a phase II clinical trial sponsored by the National Cancer Institute (NCI-1312) examining the efficacy of romidepsin for patients with relapsed, refractory or advanced CTCL, stage IB-IVA mycosis fungoides (MF) or Sézary syndrome. Skin responses were assessed by evaluation of five target lesions only. Patients with objective clinical responses in target lesions who had symptomatic nontarget lesions were allowed limited LEBT to isolated lesions for symptomatic relief. Patients who received localized radiation were not considered complete responders at any point.

RESULTS

Five patients with advanced MF (three stage IIB and two stage IVA2) received LEBT to symptomatic nontarget lesions while on a protocol with romidepsin. None of these patients experienced additional or unexpected toxicity. Four of the five patients demonstrated fast and durable responses. We noted that significantly lower than standard doses of LEBT effectively treated symptomatic lesions in these patients.

CONCLUSIONS

LEBT demonstrated significant responses at very low doses without additional toxicity in patients on protocol treatment with the histone deacetylase inhibitor romidepsin. This merits formal investigation in a clinical trial for potential synergy in patients with CTCL.

Update of the NCI multiinstitutional phase II trial of romidepsin, FK228, for patients with cutaneous or peripheral T-cell lymphoma

8027

Background: The histone deacetylase inhibitors (HDIs) are a class of differentiating agents undergoing clinical testing. Like other HDIs, romidepsin (FK228) modulates expression of genes involved in cell cycle regulation and markers of differentiation in cancer cell lines, leading to induction of differentiation or apoptosis. Romidepsin has demonstrated clinical activity in patients with T-cell lymphoma. Methods: Patients with CTCL (42) or PTCL (36) were enrolled in the NCI multi-institutional trial and assigned to cohorts based on extent of prior therapy and pathology. Romidepsin is administered on days 1, 8, and 15 of a 28 d cycle with a starting dose of 14mg/m2. Responses for patients with PTCL are measured using Cheson criteria, and CTCL using RECIST criteria. Results: Cohort one, composed of 27 patients who had previously received no more than 2 prior cytotoxic regimens of chemotherapy, has completed enrollment. Responses observed include 3 patients with CR and 7 patients with partial responses, yielding an overall response rate of 37%. Of note, responses were observed independent of stage of disease. Among 18 patients with stage IV disease, 6 patients had a complete or partial response, including 3 patients with Sézary syndrome. When including patients with greater than 2 prior cytotoxic regimens, the overall response rate was 31%. A replicate arm has been opened with the goal of confirming the response rate observed in the first cohort. Response data have not been evaluated from this arm at this time. Responses observed in 36 patients with refractory or relapsed PTCL includes 3 patients with CR and 8 patients with partial responses, comprising an overall response rate of 30%. Responses were observed independent of prior therapy, with some patients having undergone prior stem-cell transplant. Molecular endpoint analysis was performed on peripheral mononuclear cells (PBMNCs) and tumor biopsies from treated patients evaluating histone acetylation and changes in gene expression. Conclusions: Romidepsin as a single agent appears to have significant single agent activity in patients with CTCL and PTCL. Combination therapy with romidepsin may increase efficacy and should be pursued. This protocol remains open to accrual.

No significant financial relationships to disclose.

Effect of valerian, valerian/hops extracts, and valerenic acid on glucuronidation in vitro

Valerian preparations alone or in combination with hops are popular over-the-counter products used for sleep disturbances or anxiety. Therefore, it is important to characterize the effect of these products on the activity of human drug-metabolizing enzymes. The inhibitory effects of valerian and valerian/hops extracts as well as valerenic acid (a major constituent of valerian) on glucuronidation were evaluated in human liver microsomes and with expressed uridine 5'-diphosphate (UDP)-glucuronosyltransferases (UGT). Methanolic extracts of two herbal preparations caused significant reductions in the rate of formation of acetaminophen, oestradiol, morphine, and testosterone glucuronides. Oestradiol glucuronidation at the 3-hydroxy position was inhibited by nearly 87% in microsomal incubations. In addition, marked reductions in UGT1A1 and UGT2B7 activities were observed in the presence of the herbal extracts using oestradiol and morphine as probe substrates, respectively. Valerenic acid also demonstrated significant inhibitory effects on the glucuronidation of acetaminophen, oestradiol, and morphine with both microsomes and expressed UGTs. The relatively low IC50 values obtained for valerenic acid in microsomal incubations may indicate that this essential oil contributes to the effects observed with herbal extracts in inhibiting glucuronidation in vitro. Overall, these findings suggest that valerian-containing products may interfere with the glucuronidation of endo- and xenobiotics.

Evaluation of flurbiprofen urinary ratios as in vivo indices for CYP2C9 activity

AIMS

We investigated flurbiprofen pharmacokinetics in 12 volunteers to develop a phenotypic trait measure that correlates with the fractional clearance to 4'-hydroxyflurbiprofen. The effect of the CYP2C9 inhibitor fluconazole on flurbiprofen metabolism was also evaluated.

METHODS

Flurbiprofen pharmacokinetics were evaluated before and after the first and seventh doses of fluconazole. The urinary recovery ratio was calculated as FLRR = 4'-OHF/[4'-OHF + F(tot)] and the urinary metabolic ratio was calculated as FLMR = 4'-OHF/F(tot), where 4'-OHF and F(tot) represent total (conjugated and unconjugated) amounts recovered in urine.

RESULTS

There was a statistically significant relationship between the 4'-OHF formation clearance (4OHCLf) and both the 8-h FLRR and the 8-h FLMR with and without administration of fluconazole. The flurbiprofen apparent oral clearance (CL/F) was decreased by 53% [90% confidence interval (CI) -58, -48] and 64% (90% CI -69, -59), respectively, after administration of one and seven doses of fluconazole when compared with administration of flurbiprofen alone; similarly, the 4OHCLf decreased by 69% (90% CI -74, -64) and 78% (90% CI -83, -73), the 8-h FLRR decreased by 35% (90% CI -41, -29) and 40% (90% CI -46, -35) and the 8-h FLMR decreased by 61% (90% CI -65, -58) and 67% (90% CI -70, -63). The magnitude of decrease in CL/F and 4OHCLf was greater after seven doses compared with after one dose of fluconazole (P < 0.005).

CONCLUSIONS

This study provides strong evidence that both the 8-h FLRR and the 8-h FLMR are suitable phenotypic indices for CYP2C9 activity.

X-linked creatine transporter defect: a report on two unrelated boys with a severe clinical phenotype

We report two unrelated boys with the X-linked creatine transporter defect (CRTR) and clinical features more severe than those previously described with this disorder. These two boys presented at ages 12 and 30 months with severe mental retardation, absent speech development, hypotonia, myopathy and extra-pyramidal movement disorder. One boy has seizures and some dysmorphic features; he also has evidence of an oxidative phosphorylation defect. They both had classical absence of creatine peak on brain magnetic resonance spectroscopy (MRS). In one, however, this critical finding was overlooked in the initial interpretation and was discovered upon subsequent review of the MRS. Molecular studies showed large genomic deletions of a large part of the 3' end of the complete open reading frame of the SLC6A8 gene. This report emphasizes the importance of MRS in evaluating neurological symptoms, broadens the phenotypic spectrum of CRTR and adds knowledge about the pathogenesis of creatine depletion in the brain and retina.

Pharmacokinetics of intraperitoneal cefazolin and ceftazidime coadministered to CAPD patients

PURPOSE

Guidelines for empiric treatment of PD-related peritonitis published in 2000 recommend concurrent intraperitoneal (IP) cefazolin and ceftazidime. The pharmacokinetics (PK) of these agents combined have not been studied. This study was designed to determine the PK of combined IP cefazolin and ceftazidime in CAPD patients.

DESIGN

Prospective PK study in seven non-infected CAPD patients.

PROCEDURES

Patients had a peritoneal equilibration test (PET), then received one IP dose of cefazolin and ceftazidime (15 mg/kg each) co-administered over a 4-hour dwell, then performed three CAPD exchanges over the next 16 hours. Serum and dialysate samples collected over the 20-hour study period were assayed for drug concentrations by HPLC.

OUTCOME MEASURES

PK parameters.

STATISTICAL METHODS

Correlations were tested between PET and PK parameters using the Pearson-product correlation coefficient.

MAIN FINDINGS

Serum cefazolin and ceftazidime levels exceeded the minimum inhibitory concentrations for susceptible organisms (8 mg/L) throughout the 20 hour study period. Mean cefazolin and ceftazidime PK parameters included: bioavailability, 71% and 63%; elimination rate constant, 0.031 and 0.045 h -1 ; total clearance, 5.8 and 16.0 ml/min; peritoneal clearance, 1.6 and 3.9 ml/min; renal clearance, 2.3 and 3.9 ml/min, respectively. Predictive equations suggest that 1000 mg IP of cefazolin and of ceftazidime every 24 hours would produce average steady-state trough serum cefazolin and ceftazidime concentrations of 70 +/- 52 mg/L and 17 +/- 7 mg/L, respectively. There was no correlation between PET and PK parameters.

CONCLUSIONS

Co-administration did not adversely affect the PK of either agent. IP cefazolin and ceftazidime (15 mg/kg) produced adequate serum and dialysate concentrations in CAPD patients for 20 hours. PK predictions suggest that most patients would achieve adequate cefazolin and ceftazidime concentrations with 1000 mg IP once-daily. Anuric patients and those with significant residual renal function may require a more individualized approach.

The effect of trimethoprim on CYP2C8 mediated rosiglitazone metabolism in human liver microsomes and healthy subjects

AIMS

Rosiglitazone, a thiazolidinedione antidiabetic medication used in the treatment of Type 2 diabetes mellitus, is predominantly metabolized by the cytochrome P450 (CYP) enzyme CYP2C8. The anti-infective drug trimethoprim has been shown in vitro to be a selective inhibitor of CYP2C8. The purpose of this study was to evaluate the effect of trimethoprim on the CYP2C8 mediated metabolism of rosiglitazone in vivo and in vitro.

METHODS

The effect of trimethoprim on the metabolism of rosiglitazone in vitro was assessed in pooled human liver microsomes. The effect in vivo was determined by evaluating rosiglitazone pharmacokinetics in the presence and absence of trimethoprim. Eight healthy subjects (four men and four women) completed a randomized, cross-over study. Subjects received single dose rosiglitazone (8 mg) in the presence and absence of trimethoprim 200 mg given twice daily for 5 days.

RESULTS

Trimethoprim inhibited rosiglitazone metabolism both in vitro and in vivo. Inhibition of rosiglitazone para-hydroxylation by trimethoprim in vitro was found to be competitive with apparent K(i) and IC(50) values of 29 microm and 54.5 microm, respectively. In the presence of trimethoprim, rosiglitazone plasma AUC was increased by 31% (P = 0.01) from 2774 +/- 645 microg l(-1) h to 3643 +/- 1051 microg l(-1) h (95% confidence interval (CI) for difference 189, 1549), and half-life was increased by 27% (P = 0.006) from 3.3 +/- 0.5 to 4.2 +/- 0.8 h (95% CI for difference 0.36, 1.5). Trimethoprim reduced the para-O-sulphate rosiglitazone/rosiglitazone and the N-desmethylrosiglitazone/rosiglitazone AUC(0-24) ratios by 22% and 38%, respectively.

CONCLUSIONS

These results indicate that trimethoprim is a competitive inhibitor of CYP2C8-mediated rosiglitazone metabolism in vitro and that trimethoprim administration increases plasma rosiglitazone concentrations in healthy subjects.

"SIRT8" expressed in thyroid cancer is actually SIRT7

British Journal of Cancer (2002) 87, 1479–1479. doi:10.1038/sj.bjc.6600635www.bjcancer.com

© 2002 Cancer Research UK

Minimal in vivo activation of CYP2C9-mediated flurbiprofen metabolism by dapsone

Dapsone has been shown to activate flurbiprofen 4'-hydroxylation by expressed CYP2C9 enzyme and in human liver microsomes. It has been suggested that this observation is due to substrate cooperativity on enzyme activity; however, the in vivo relevance of this observation is unknown. Thus, the purpose of this study was to evaluate whether dapsone can act cooperatively with flurbiprofen to activate the in vivo metabolism of flurbiprofen to 4'-hydroxyflurbiprofen. Twelve healthy subjects received single-dose flurbiprofen 50 mg on three occasions: alone (visit A); 2 h after a single dapsone 100-mg dose (visit B); and 2 h after the seventh daily dose of dapsone 100 mg (visit C). Concentrations of flurbiprofen and 4'-hydroxy flurbiprofen in plasma and urine and dapsone and N-acetyldapsone in plasma were determined by HPLC. Flurbiprofen pharmacokinetic parameters for the three visits were estimated by non-compartmental methods and compared in the absence and presence of dapsone. Flurbiprofen apparent oral clearance was increased by approximately 11% (P < 0.02) after dapsone 100 mg for 7 days. Dapsone plasma concentrations averaged 5 +/- 2 microM after a single dose and 11 +/- 4 microM after seven daily 100 mg doses. These dapsone plasma concentrations were within the range of concentrations producing activation of flurbiprofen metabolism by CYP2C9 in vitro. These results are consistent with the hypothesis that dapsone does influence flurbiprofen metabolism in vivo in a cooperative way to enhance metabolism. However, the magnitude of effect is substantially less than observed in vitro.

Intravenous vancomycin pharmacokinetics in automated peritoneal dialysis patients

The pharmacokinetics of intravenous (i.v.) vancomycin was studied in automated peritoneal dialysis (APD) patients who received a single i.v. dose of vancomycin (15 mg/kg total body weight). Dialysate samples were collected at the beginning, middle, and end of dwells 1-3 (on-cycler), and at the end of dwells 4 and 5 (off-cycler), for a 24-hour period. Blood samples were collected at the beginning, middle, and end of dwells 1-3 (on-cycler), and at the end of dwell 5 (off-cycler) for a 24-hr period. Pharmacokinetics parameters were calculated assuming a one-compartment model. Glomerular filtration rate (GFR) and vancomycin clearance (CI) values were normalized to 1.73 m2. Ten patients [4 males, 6 females; 47.4 +/- 9.9 years of age (mean +/- SD)] who had received PD for a median 3.5 months (range 2-66 months) were studied. Dwell times were 2.3 +/- 0.1 hours on cycler and 7.3 +/- 0.1 hours off cycler. Vancomycin half-life was significantly different on-cycler than off-cycler (11.6 +/- 5.2 hr vs 62.8 +/- 33.0 hr; p < 0.001). Vancomycin total CI (CI(T)) was 7.4 +/- 2.0 mL/min. Renal CI (CI(R)) and PD CI (CI(PD)) accounted for 23.6% and 28.0% of CI(T). respectively. CI(R) correlated with GFR (CI(R) = 0.90 GFR - 1.01; r2 = 0.79; p = 0.008). Mean vancomycin serum and dialysate end-of-dwell concentrations were above minimum inhibitory concentration of susceptible organisms (5 micro/mL) for the first cycler and the second ambulatory exchanges only. The results of this study suggest that, to provide adequate concentrations for susceptible organisms over a 24-hour period, current intermittent vancomycin dosing recommendations for PD-related peritonitis need to be changed to 35 mg/kg intraperitoneally on day 1, then 15 mg/kg i.p. thereafter (i.e., once daily) in APD patients.

High-performance liquid chromatographic assay for acetaminophen glucuronide in human liver microsomes

A rapid and specific high-performance liquid chromatographic assay was developed for the determination of acetaminophen glucuronide formed by human liver microsomes. In addition, incubation conditions were systematically evaluated. Conditions that yielded the optimal rate of acetaminophen glucuronide formation over various concentrations of acetaminophen (0.15-30 mM) consisted of the following: 0.1 M potassium phosphate buffer, 1 mM magnesium chloride, 30 microg/mg alamethicin, 4 mM uridine 5'-diphosphoglucuronic acid at a pH of 7.1. Alamethicin produced higher and more consistent APAPG formation rates compared to Brij-58. Adding saccharolactone to the incubation medium reduced the velocity of the reaction. Acetaminophen glucuronide, acetaminophen, and the internal standard (paraxanthine), were analyzed on a C18 column with UV detection at 250 nm. The mean correlation coefficient (r2) of the standard curves for acetaminophen glucuronide was >0.99 over the range of 0.1-25 nmol. The intra- and inter-day coefficients of variation were <4%. This method is suitable for in vitro studies using acetaminophen glucuronide formation as an index reaction for UGT activity.

Cefazolin dialytic clearance by high-efficiency and high-flux hemodialyzers

Cefazolin dialytic clearance has not been determined in patients undergoing hemodialysis with high-efficiency or high-flux dialyzers. The objective of this study is to determine the pharmacokinetics and dialytic clearance of cefazolin and develop dosing strategies in these patients. Twenty-five uninfected subjects undergoing chronic thrice-weekly hemodialysis were administered a single dose of intravenous cefazolin (15 mg/kg) after their standard hemodialysis session. Fifteen subjects underwent hemodialysis with high-efficiency hemodialyzers, and 10 subjects underwent hemodialysis with high-flux hemodialyzers. Blood and urine samples were collected serially over the interdialytic period, during the next intradialytic period, and immediately after the next hemodialysis session. Serum and urine concentrations of cefazolin were determined by high-performance liquid chromatography. Differential equations describing a two-compartment model were fit to the cefazolin serum concentration-time data over the study period, and pharmacokinetic parameters were determined. Mean dialytic clearance values for cefazolin were significantly greater in the high-flux group compared with the high-efficiency group (30.9 +/- 6.52 versus 18.0 +/- 6.26 mL/min, respectively; P: < 0.05). Cefazolin reduction ratios were significantly greater (0.62 +/- 0.08 versus 0.50 +/- 0.07; P: < 0.005) in the high-flux group compared with the high-efficiency group and correlated well with equilibrated urea reduction. The pharmacokinetic model developed from patient data was used to simulate cefazolin serum concentration data for high-efficiency and high-flux dialyzers. Cefazolin doses of 15 or 20 mg/kg after each hemodialysis session maintained adequate serum concentrations throughout a 2- or 3-day interdialytic period regardless of hemodialyzer type.

Characterization of tubular functional capacity in humans using para-aminohippurate and famotidine

BACKGROUND

Renal drug excretion by glomerular filtration and active tubular secretion may be altered by factors such as acute and chronic renal disease, nephrotoxins, and drug interactions. Thus, accurate and reproducible methods for quantitation of glomerular filtration rate (GFR) and tubular functional capacity are critical.

METHODS

We utilized a four-step sequential infusion method to characterize anionic [para-aminohippurate (PAH)] and cationic (famotidine) tubular functional capacity in healthy volunteers. Filtration and secretion rates were quantitated from renal clearance and iothalamate-derived GFR determinations.

RESULTS

Concentration-dependent renal clearance of PAH was observed at plasma concentrations> 100 mg/L; renal clearances were 442 +/- 131 (mean +/- SD), 423 +/- 94, 233 +/- 45, and 152 +/- 18 mL/min/1.73 m2 at plasma concentrations of 18 +/- 2, 92 +/- 5, 291 +/- 47 and 789 +/- 28 mg/L, respectively. The apparent affinity (Km) and maximum secretory capacity (TmPAH) were 141 +/- 70 mg/L and 71 +/- 16 mg/min/1.73 m2, respectively. The unbound renal clearance and tubular secretory clearance of famotidine were 384 +/- 70 and 329 +/- 78 mL/min/1.73 m2, respectively, and were not significantly correlated with the unbound plasma concentrations, which ranged from 126 to 2659 ng/mL. The rate of tubular secretion was linear at unbound plasma concentrations up to 2659 ng/mL.

CONCLUSIONS

These data indicate that a sequential infusion method using PAH may be used to characterize the anionic secretory component of proximal tubular function. The tubular clearance of famotidine may be a suitable index of the cationic secretory capacity of the proximal tubule in humans. Saturation of the cationic secretory pathway was not observed, and further investigation into parallel pathways of cationic secretion, such as p-glycoprotein, may be warranted.

Sensitive and specific high-performance liquid chromatographic assay for 4'-hydroxyflurbiprofen and flurbiprofen in human urine and plasma

A high-performance liquid chromatographic assay has been developed for the simultaneous quantitation of flurbiprofen and its major metabolite, 4'-hydroxyflurbiprofen, in urine and plasma. No extraction procedure was necessary for analysis of these compounds, which reduced time involved in sample preparation. The analytes were separated on a Brownlee Spheri-5 C18 column with a mobile phase of acetonitrile-20 mM dibasic potassium phosphate pH 3 buffer (40:60, v/v). Fluorescence detection was utilized with an excitation wavelength of 260 nm and an emission wavelength of 320 nm, providing excellent sensitivity. The limit of quantitation for 4'-hydroxyflurbiprofen and flurbiprofen was 0.25 microg/ml in urine and 0.05 microg/ml and 0.25 microg/ml, respectively, in plasma. All components were eluted within 16 min. Intra-day, inter-day, freeze-thaw, and in process stability were tested for both compounds and the coefficient of variation was less than 14% in all cases. This method provides a sensitive and specific assay for the detection of flurbiprofen and 4'-hydoxyflurbiprofen in urine and plasma and is suitable for use in in vivo studies evaluating the regulation of CYP2C9 activity.

Effect of ceftazidime on systemic cytokine concentrations in rats

The effect of a single dose of ceftazidime on circulating concentrations of interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-alpha) in a rat model of sepsis was studied. IL-6 concentrations were significantly elevated (100 to 200 times the baseline) 6 h after ceftazidime administration in both septic and nonseptic (control) rats. TNF-alpha concentrations increased significantly in nonseptic (approximately 40 times the baseline) rats but not septic (approximately 2 to 3 times the baseline) rats. Ceftazidime administration was not associated with an increase in endotoxin concentrations. These findings suggest that ceftazidime modulation of proinflammatory cytokine concentrations may be independent of its antimicrobial properties.

Intermittent intravenous piperacillin pharmacokinetics in automated peritoneal dialysis patients

BACKGROUND

Use of intermittent antibiotic dosing is increasing in the treatment of peritoneal dialysis (PD)-related peritonitis. We studied the pharmacokinetics of intravenous (i.v.) piperacillin in automated PD patients.

PATIENTS AND METHODS

Eight patients (3 males, 5 females) were recruited and received a single i.v. dose of piperacillin (35 mg/kg actual body weight). Blood and dialysate samples were collected at the beginning, middle, and end of dwells 1-3 (on cycler), and end of dwells 4-5 (off cycler) for a 24-hour period. Baseline and 24-hour urine samples (nonanuric patients, n = 7) were collected. Pharmacokinetic parameters were calculated assuming a one-compartment model. Glomerular filtration rate (GFR) and piperacillin clearance (CL) values were normalized to 1.73 m2.

RESULTS

The patients were 49.5 +/- 10.1 years of age (mean +/- SD) and had been receiving PD for a median of 3 months (range 2-66 months). Dwell times were 2.25 +/- 0.06 hours on cycler and 7.26 +/- 0.14 hours off cycler. Piperacillin half-life was not statistically different on or off the cycler (on cycler 1.99 +/- 0.39 hr, off cycler 4.39 +/- 5.4 hr; p = 0.12) and remained insignificant, even accounting for an outlier (on cycler 2.01 +/- 0.41 hr, off cycler 2.54 +/- 1.48 hr; p = 0.19). Piperacillin total CL (CL(T)) was 31.29 +/- 6.02 mL/minute. Renal CL (CL(R)) and PD CL (CL(PD)) accounted for 8.8% and 16.8% of CL(T); CL(R) correlated well with GFR (CL(R) = 0.86 GFR + 0.1; p < 0.00003). Mean piperacillin serum and dialysate end-of-dwell concentrations were above minimum inhibitory concentration of susceptible organisms (8 microg/mL) for the three cycler exchanges only. Serum and dialysate concentrations predicted using a one-compartment model suggest that i.v. piperacillin 4000 mg would provide adequate concentrations for susceptible organisms over a 12-hour period.

CONCLUSION

The current i.v. piperacillin dosing recommendations of 4000 mg every 12 hours for PD-related peritonitis are appropriate for patients on automated PD. Intermittent intraperitoneal piperacillin is not recommended.

In vivo modulation of CYP enzymes by quinidine and rifampin

BACKGROUND

The metabolism of drugs and other xenobiotics is mediated by enzymes whose activities can be modulated by different compounds. The activities of these modulators have the potential to be used to optimize drug action, prevent toxicity, or identify the enzymes involved in a reaction. This approach requires that selective agents be used for specific enzymes. However, selectivity of action has been poorly characterized in vivo.

METHODS

This study investigated the effect of 3 and 28 days of treatment with quinidine (200 mg daily) and rifampin (INN, rifampicin) (600 mg daily) on the activities of four cytochrome P450 enzymes and N-acetyltransferase in 28 healthy young male volunteers divided into three groups with a cocktail of drug probes used, including caffeine, mephenytoin, debrisoquin (INN, debrisoquine), and dapsone.

RESULTS

Quinidine selectively and almost completely inhibited the activity of CYP2D6 from day 3 through day 28 without affecting any other enzymes. Rifampin showed evidence of time-dependent induction of the activities of all measured oxidative routes of metabolism but decreased the acetylation ratio in fast acetylators. The quinidine/rifampin combination resulted in selective CYP2D6 inhibition and induction of all other enzymes evaluated over this time period, suggesting that predictable complex interactions occur with the drug combination.

CONCLUSIONS

These observations illustrate the value of simultaneous assessment of the effect of modulators on the activities of multiple specific enzymes with the drug cocktail approach.

Nalmefene to prevent epidural narcotic side effects in pediatric patients: a pharmacokinetic and safety study

STUDY OBJECTIVE

To determine the pharmacokinetics and preliminary efficacy of nalmefene in children in preventing epidural-induced narcotic side effects.

DESIGN

Double-blind, placebo-controlled study.

SETTING

University-affiliated children's hospital.

PATIENTS

Thirty-four children (aged 2-12 yrs) undergoing cardiothoracic surgery with epidural anesthesia.

INTERVENTIONS

Patients were randomized to receive intravenous bolus nalmefene 1 microg/kg or placebo.

MEASUREMENTS AND MAIN RESULTS

Six blood samples (one before nalmefene administration and five from 13 randomly designated time points) from each patient were assayed to determine plasma nalmefene concentrations. Patients were assessed for pain, nausea, vomiting, and urinary retention for 24 hours after administration. Concentration-time data were analyzed by a limited sampling strategy with adult pharmacokinetic parameters used as Bayesian priors. A two-compartment, first-order model was fitted to the data using ADAPT II. Pharmacokinetic parameter estimates in these patients were similar to values reported in adults. The initial disposition half-life (t(1/2alpha)) was 0.36+/-0.11 hour, the terminal elimination half-life (t(1/2beta)) 8.7+/-2.3 hours, clearance 0.729+/-0.172 L/kg/hr, and steady-state volume of distribution 7.21+/-2.49 L/kg. Ability to prevent epidural narcotic-induced side effects could not be documented at the 1-microg/kg dose. No statistically significant differences were noted between study and placebo groups with regard to pain, nausea, vomiting, or urinary retention.

CONCLUSION

Nalmefene has similar pharmacokinetics in children as in adults. It was administered safely to these patients and did not produce unmanageable pain.

Long-term clinical outcome in the Bypass Angioplasty Revascularization Investigation Registry: comparison with the randomized trial. BARI Investigators

BACKGROUND

The Bypass Angioplasty Revascularization Investigation (BARI) included 4039 patients with multivessel coronary artery disease; 1829 consented to randomization, and 2010 did not but were followed up in a registry. Thus, we can evaluate the outcome of physician-guided versus random assignment of percutaneous transluminal coronary angioplasty (PTCA) versus coronary artery bypass graft surgery (CABG).

METHODS AND RESULTS

We compared the baseline features and outcomes for PTCA and CABG in the overall registry and its predesignated subgroups. We assessed the impact of treatment by choice versus random assignment by comparing the results in the registry with those of the randomized trial. Statistical adjustments for differences in baseline characteristics were made. Within the registry, nearly twice as many patients were selected for PTCA (1189) as CABG (625); mortality at 7 years was similar for PTCA (13.9%) and CABG (14.2%) (P=0.66) before and after adjustment for baseline differences between patients selected for PTCA versus CABG (adjusted RR, 1.02; P=0.86). In contrast to the randomized trial, the 7-year mortality rate of treated diabetics in the registry was equally high (26%) with PTCA or CABG. Seven-year mortality was higher for patients undergoing PTCA in the randomized trial than in the registry (19.1% versus 13.9%, P<0.01) but not for those undergoing CABG (15.6% versus 14.2%, P=0.57). The adjusted relative mortality risk for PTCA in the randomized versus registry population was 1.17 (P=0.16).

CONCLUSIONS

BARI physicians were able to select PTCA rather than CABG for 65% of registry patients who underwent revascularization without compromising long-term survival either in the overall population or in treated diabetics.

Determinants of ceftriaxone clearance by continuous venovenous hemofiltration and hemodialysis

STUDY OBJECTIVE

To guide individual ceftriaxone dosages in patients receiving continuous renal replacement therapy.

DESIGN

Prospective, outpatient study.

SETTING

University-affiliated general clinical research center.

PATIENTS

Eight patients receiving hemodialysis.

INTERVENTION

We performed controlled clearance studies with three hemofilters: an acrylonitrile copolymer 0.6 m2 (AN69), polymethylmethacrylate 2.1 m2 (PMMA), and polysulfone 0.65 m2 (PS).

MEASUREMENTS AND MAIN RESULTS

Subjects received ceftriaxone 1000 mg intravenously before the start of a clearance study. The concentration of ceftriaxone in multiple plasma and dialysate-ultrafiltrate samples was determined by high-performance liquid chromatography. The diffusional clearances (Cl(diffusion)) and sieving coefficients (SC) of ceftriaxone, urea, and creatinine were compared by a mixed-model repeated-measures analysis of variance with filter and blood, dialysate inflow, or ultrafiltration rate as the main effect and patient as a random effect. The fraction of ceftriaxone bound to plasma proteins was 43 +/- 15% (range 13-92%). Concentration dependence was evident in all three groups. The fraction unbound to plasma proteins (f(up)) at the time that SCs were determined was significantly lower in the PS group (0.16 +/- 0.07) than the AN69 group (0.30 +/- 0.17, p<0.01), but similar to that in the PMMA group (0.27 +/- 0.12). Despite the higher f(up), the SC of unbound ceftriaxone with the AN69 filter (0.48 +/- 0.13) was significantly lower than values for the PMMA (0.86 +/- 0.33) and PS (0.82 +/- 0.22) groups (p<0.05). Continuous venovenous hemofiltration clearance of urea and unbound ceftriaxone increased significantly only for the PMMA (p=0.006) and PS (p=0.015) filters when the ultrafiltration rate was increased. Significant linear relationships (p<0.0001) were observed between Cl(diffusion) of unbound ceftriaxone and clearance of urea for all three filters: AN69 slope = 0.57, PMMA slope = 0.90, and PS slope = 1.02. The slope of this relationship for the AN69 filter was significantly lower than for the other two filters.

CONCLUSION

Ceftriaxone clearance was significantly increased and membrane dependent during continuous venovenous hemofiltration and continuous venovenous hemodialysis. Thus individual ceftriaxone dosages for patients receiving continuous renal replacement therapies should incorporate extracorporeal clearance.

Sex differences in the pharmacokinetics of dehydroepiandrosterone (DHEA) after single- and multiple-dose administration in healthy older adults

The pharmacokinetics of exogenously administered DHEA have not been well characterized despite its increasing use in therapeutic and research investigations. The purpose of this study was to evaluate the pharmacokinetics of DHEA and its sulfated metabolite (DHEA-S) after single- and multiple-dose oral administration of DHEA 200 mg. Healthy older adult volunteers (7 women, 6 men) ages 65 to 79 years were studied on five visits separated by 1 week. Subjects received daily administration of placebo (days 1 to 7), DHEA 200 mg (days 8 to 22), and placebo (days 23 to 29). Blood samples were collected over 24 hours on days 1, 8, 15, 22, and 29 for DHEA and DHEA-S determinations by RIA. Pharmacokinetic parameter estimates were calculated by noncompartmental methods. Administration of DHEA 200 mg resulted in higher DHEA Cmax, AUC, and overall concentrations in women than in men (p < 0.03); DHEA-S parameter estimates were similar between men and women. Following a single dose of DHEA 200 mg, DHEA concentrations increased 5- to 6-fold in both men and women, and DHEA-S concentrations increased 5-fold in men and 21-fold in women relative to endogenous concentrations. The results of this study indicate that the pharmacokinetics of DHEA differ between older men and women.

Determinants of ceftazidime clearance by continuous venovenous hemofiltration and continuous venovenous hemodialysis

Although several dosage adjustment regimens have been proposed, there is little quantitative information to guide the initiation of ceftazidime therapy in patients who are receiving continuous renal replacement therapy. To determine the clearance of ceftazidime by continuous venovenous hemofiltration (CVVH) and continuous venovenous hemodialysis (CVVHD), we performed controlled clearance studies with stable hemodialysis patients with three hemofilters: a 0.6-m(2) acrylonitrile copolymer (AN69; Hospal) filter, a 2.1-m(2) polymethylmethacrylate filter (PMMA; Toray) filter and a 0.65-m(2) polysulfone (PS; Fresenius) filter. Subjects received 1,000 mg of ceftazidime intravenously prior to the start of a clearance study. The concentration of ceftazidime in multiple plasma and dialysate or ultrafiltrate samples was determined by high-performance liquid chromatography. The diffusional clearances (CI(diffusion)) and sieving coefficients of ceftazidime were compared by a mixed-model repeated-measures analysis of variance with filter and blood, dialysate inflow, or ultrafiltration rate as the main effect and the patient as a random effect. The fraction of ceftazidime bound to plasma proteins was 17%+/-7% (range, 10 to 25%). The clearances of ceftazidime, urea, and creatinine by CVVHD were essentially constant at blood flow rates of 75 to 250 ml/min for all three filters. Significant linear relationships (P<0.0001) were observed between CI(diffusion) of ceftazidime and clearance of urea for all three filters: AN69 (slope = 0.83), PMMA (slope = 0.89), and PS (slope = 1.03). Ceftazidime clearance was membrane independent during CVVH and CVVHD. CVVH and CVVHD can significantly augment the clearance of ceftazidime. Dosing strategies for initiation of ceftazidime therapy in patients receiving CVVH and CVVHD are proposed.

Evaluation of the influence of diabetes mellitus on antipyrine metabolism and CYP1A2 and CYP2D6 activity

STUDY OBJECTIVE

To evaluate the metabolism of antipyrine, a general metabolic probe, caffeine, a probe for cytochrome P450 (CYP) 1A2 and N-acetyltransferase activity, and dextromethorphan, a specific probe for CYP2D6 activity in patients with type 1 or 2 diabetes mellitus.

DESIGN

Prospective, controlled study.

SETTING

Research facility. Patients. Fifteen patients with type 1 and 16 with type 2 diabetes, and 16 healthy controls.

INTERVENTION

Each subject simultaneously received antipyrine 10 mg/kg, caffeine 100 mg, and dextromethorphan 30 mg.

MEASUREMENTS AND MAIN RESULTS

The pharmacokinetics of antipyrine and its primary metabolites were determined from saliva and urine samples. Type 1 diabetes had marked effects on antipyrine metabolism whereas type 2 disease did not alter the metabolism of any of the probe drugs. The apparent oral clearance of antipyrine was increased 72% in patients with type 1 disease compared with controls (p=0.0001). In addition, formation clearances of 4-hydroxyantipyrine and 3-hydroxymethylantipyrine were increased by 74% and 137% in those patients relative to controls. The caffeine metabolic index (paraxanthine/caffeine) was increased 34% (p=0.11), and N-acetylation and CYP2D6 phenotype were not altered.

CONCLUSION

The metabolism of antipyrine is increased in patients with type 1 diabetes. Based on in vitro reports of antipyrine metabolism and current caffeine metabolic index data, the predominant effect of type 1 diabetes appears to be an increase in CYP1A2 activity. Assessment of the effect of the disease on other specific CYP metabolic pathways is warranted.

Effect of disulfiram-mediated CYP2E1 inhibition on the disposition of vesnarinone

Vesnarinone is an orally administered inotropic agent that is metabolized in vitro by the cytochrome P450 (CYP) isozymes CYP3A4 and CYP2E1. The purpose of this study was to assess the contribution of CYP2E1 activity to the disposition of vesnarinone in humans by characterizing the pharmacokinetics before and after disulfiram-mediated CYP2E1 inhibition. The pharmacokinetics of vesnarinone 60 mg were determined in normal healthy volunteers (N = 7) before and after daily disulfiram administration (250 mg). Chlorzoxazone 250 mg was also administered before, during, and after disulfiram administration to serve as a positive control for CYP2E1 inhibition. Disulfiram treatment decreased 6-hydroxychlorzoxazone formation clearance by nearly 95% but effected only a modest decrease in vesnarinone apparent oral clearance (5.7 +/- 1.0 vs. 5.0 +/- 0.5 ml/min; p = 0.022). In contrast to the modest effect on the parent drug, disulfiram treatment substantially increased plasma concentrations of the primary metabolite OPC-18692. The Cmax of OPC-18692 was increased approximately 7-fold, and the area under the plasma concentration-time curve was increased 18-fold (2.9 +/- 0.9 vs. 53.7 +/- 33.2 micrograms.h/ml; p = 0.006). The results indicate that CYP2E1 inhibition has only a modest, clinically insignificant effect on vesnarinone disposition but markedly increases plasma concentrations of the OPC-18692 metabolite. The pharmacological properties of this metabolite have not been fully defined; thus, the clinical importance of this observation depends on whether this metabolite contributes to any of the toxicity associated with vesnarinone administration.

Determination of famotidine in human plasma and urine by high-performance liquid chromatography

An improved, rapid and specific high-performance liquid chromatographic assay was developed for the determination of famotidine in human plasma and urine. Plasma samples were alkalinized and the analyte and internal standard (cimetidine) extracted with water-saturated ethyl acetate. The extracts were reconstituted in mobile phase, and injected onto a C18 reversed-phase column; UV detection was set at 267 nm. Urine samples were diluted with nine volumes of a mobile phase-internal standard mixture prior to injection. The lower limits of quantification in plasma and urine were 75 ng/ml and 1.0 microg/ml, respectively; intra- and inter-day coefficients of variation were < or =10.5%. This method is currently being used to support renal function studies assessing the use of intravenously administered famotidine to characterize cationic tubular secretion in man.

Comparison of iothalamate clearance methods for measuring GFR

STUDY OBJECTIVE

To evaluate the bias and precision of three methods of measuring glomerular filtration rate (GFR) relative to a standard method.

DESIGN

Prospective, outpatient study.

SETTING

University-affiliated general clinical research center.

PATIENTS

Twenty-six patients with various degrees of renal function (GFR range 25-151 ml/min/1.73 m2).

INTERVENTIONS

Each patient received iothalamate twice during the study visit, first as a bolus injection and then as a priming dose followed by a constant-rate infusion for 2.5 hours.

MEASUREMENTS AND MAIN RESULTS

Plasma (ClpIVB) and renal clearances (ClrIVB) after bolus injection and plasma clearance during constant-rate infusion (ClpINF) were compared with standard renal clearance during constant-rate infusion (ClrINF). All three measures were highly correlated with ClrINF (r>0.90, p<0.001). The mean ClrIVB was not significantly different from ClrINF (106.3+/-30.4 vs 104.2+/-28.5 ml/min/1.73 m2) and provided a precise (8.8%, 95% CI 6.5-11.1%) and unbiased measure of GFR. Both ClpIVB and ClpINF were positively biased; values exceeded ClrINF by 11.8+/-11.1 (p=0.0001) and 10.5+/-12.5 ml/min/1.73 m2 (p=0.0003), respectively. Use of a nonrenal correction factor of 9.8 and 10.5 ml/min/1.73 m2 for infusion and bolus plasma clearance values, respectively, eliminated bias and improved the precision of these methods.

CONCLUSIONS

Iothalamate renal clearance after bolus injection is a simple, accurate, and precise measurement of GFR and may be a useful alternative to the standard infusion method in clinical investigations. The corrected plasma clearance provides a simple index of GFR for clinical practice.

Radar and optical observations of asteroid 1998 KY26

Observations of near-Earth asteroid 1998 KY26 shortly after its discovery reveal a slightly elongated spheroid with a diameter of about 30 meters, a composition analogous to carbonaceous chondritic meteorites, and a rotation period of 10.7 minutes, which is an order of magnitude shorter than that measured for any other solar system object. The rotation is too rapid for 1998 KY26 to consist of multiple components bound together just by their mutual gravitational attraction. This monolithic object probably is a fragment derived from cratering or collisional destruction of a much larger asteroid.

DHEA and DHEA-S: a review

Dehydroepiandrosterone (DHEA) and its sulfated metabolite DHEA-S are endogenous hormones secreted by the adrenal cortex in response to adrenocorticotrophin (ACTH). Much has been published regarding potential effects on various systems. Despite the identification of DHEA and DHEA-S more than 50 years ago, there is still considerable controversy as to their biological significance. This article reviews the metabolism and physiology of DHEA and DHEA-S, the influence of age and gender on concentrations, and changes in endogenous concentrations associated with disease states and other factors, including diet and exercise. This article is unique in that it also summarizes the influence of drugs on DHEA and DHEA-S concentrations, as well as concentrations of DHEA and DHEA-S observed after the administration of DHEA by various routes. Sections of the article specifically address DHEA and DHEA-S concentrations as they relate to stress, central nervous system function and psychiatric disorders, insulin sensitivity, immunological function, and cardiovascular disorders.

Pharmacokinetics of intermittent intraperitoneal ceftazidime

Ceftazidime is currently recommended as an alternative first-line agent in the treatment of peritonitis and for Pseudomonas peritonitis. The pharmacokinetics of intermittent intraperitoneal (i.p.) ceftazidime have been poorly characterized. This study was designed to characterize the pharmacokinetic disposition of a single dose of ceftazidime in anuric and non-anuric CAPD patients, over 48 hours. This was a prospective, open label, pharmacokinetic study. The study was conducted in an independent, outpatient dialysis center. Ten volunteer continuous ambulatory peritoneal dialysis (CAPD) patients with and without residual renal function, no peritonitis or antibiotics in the previous 4 weeks, and on CAPD for at least 2 months were recruited. Patients received a single dose of i.p. ceftazidime (15 mg/kg) in the first daytime exchange over a 6-hour dwell, after an overnight dwell. Serum, urine, and dialysate were collected over a 48-hour period. A high-pressure liquid chromatography (HPLC) assay was used to analyze ceftazidime in these samples. Pharmacokinetic parameters were calculated. Six of the 10 patients were non-anuric with a mean residual renal creatinine clearance of 2.9 +/- 1.6 mL/min. The mean +/- SD bioavailability was 72% +/- 14%, and the volume of distribution was 0.34 +/- 0.08 L/kg. The mean serum elimination half-life of 22 +/- 5 hours. The peritoneal clearance was 5.74 +/- 1.6 mL/min. No difference was detected between anuric and nonanuric patients. Mean plasma and dialysate concentrations at 24 hours were 24 +/- 6 microg/mL and 18 +/- 7 microg/mL, respectively, and were 12.0 +/- 3.6 microg/mL and 7.4 +/- 3.1 microg/mL at 48 hours, respectively. Once-daily i.p. dosing of ceftazidime achieves serum and dialysate levels greater than the MIC of sensitive organisms over 48 hours.

Pharmacokinetics of intermittent intraperitoneal cefazolin in continuous ambulatory peritoneal dialysis patients

OBJECTIVE

To investigate the pharmacokinetic parameters of intermittent intraperitoneal (IP) cefazolin, and recommend a cefazolin dosing regimen in continuous ambulatory peritoneal dialysis (CAPD) patients.

DESIGN

Prospective nonrandomized open study.

SETTING

CAPD outpatient clinic in Albany, New York.

PATIENTS

Seven volunteer CAPD patients without peritonitis. Three of the patients were nonanuric while 4 were anuric.

INTERVENTIONS

Cefazolin (15 mg/kg total body weight) was given to each patient during the first peritoneal exchange. Blood and dialysate samples were collected at times 0, 0.5, 1,2,3,6 (end of the first antibiotic-containing dwell), 24, and 48 hours after the administration of IP cefazolin. Urine samples were collected in nonanuric patients over the study period.

RESULTS

The mean+/-SD amount of cefazolin dose absorbed from the dialysate after the 6-hour dwell was 69.7%+/-8.0% of the administered dose. The cefazolin absorption rate constant from dialysate to serum was 0.21+/-0.1/hr (absorption half-life 3.5+/-0.8 hr). The mean serum concentrations reached at 24 and 48 hours were 52.4+/-3.7 mg/L and 30.3+/-5.9 mg/L, respectively. The mean dialysate cefazolin concentrations reached at 24 and 48 hours were 15.1+/-3.4 mg/L and 7.9+/-1.4 mg/L, respectively. The cefazolin serum elimination rate constant was 0.02+/-0.01/hr (elimination half-life 31.5+/-8.8 hr). The total cefazolin body clearance was 3.4+/-0.6 ml/min. In the 3 nonanuric patients the mean renal clearance of cefazolin was 0.6+/-0.4 ml/min. The peritoneal clearance of cefazolin was 1.0+/-0.3 mL/min. The systemic volume of distribution of cefazolin was 0.2+/-0.05 L/kg. No statistical difference was detected in pharmacokinetic parameters between anuric and nonanuric patients, although this may be due to the small number of patients in each group.

CONCLUSION

A single daily dose of cefazolin dosed at 15 mg/kg actual body weight in CAPD patients is effective in achieving serum concentration levels greater than the minimum inhibitory concentration for sensitive organisms over 48 hours, and dialysate concentration levels over 24 hours. Caution is warranted in extrapolation of dosing recommendations to patients who maintain a significant degree of residual renal function.

Evaluation of gentamicin pharmacokinetics and dosing protocols in 195 neonates

Gentamicin pharmacokinetics and dosing protocols in neonates were studied. Demographic and pharmacokinetic data on 202 neonates treated with gentamicin at a 500-bed medical center were collected over a three-year period. Administered doses, gentamicin concentration measurements, and recorded times were used to calculate each patient's clearance, volume of distribution, elimination rate constant, and half-life. The performance of 15 dosing protocols, including 6 previously published ones and 9 developed on the basis of the study, was evaluated using the pharmacokinetic data. Of the 202 patients, 195 were included in the analysis. The mean +/- S.D. clearance, volume of distribution, elimination rate constant, and half-life were 0.047 +/- 0.015 L/hr/kg, 0.45 +/- 0.11 L/kg, 0.107 +/- 0.032 L/hr, and 7.19 +/- 2.64 hours, respectively. Weight, urine output, gestational age, and postconceptional age (PCA) had the highest correlation with the pharmacokinetic values. Blood urea nitrogen concentration (BUN) and Apgar score were poor predictors of the pharmacokinetic values. There were no significant differences among patient subsets based on race and BUN, but subset analysis based on PCA did indicate significant differences. In simulations, the protocols based on the study patients tended to perform better than the literature protocols, with all but three achieving therapeutic goals in 75% or more of the neonates. Of the published protocols, Murphy and Carter's produced the greatest percentage of neonates with peaks from 5 to 10 mg/L and troughs of <2 mg/L. The devised protocols tended to perform poorly in producing troughs between 1 and 2 mg/L, yet performed comparatively well in providing therapeutic peaks from 5 to 10 mg/L.

A neighborly way to reduce Medicaid costs

One of the keys to controlling the costs of Medicaid managed care patients is to treat them before they become ill. Richard Frye, Ph.D., profiles the Community Health Worker Outreach Program in Baltimore, which trains residents of neighborhoods with high numbers of Medicaid beneficiaries how to teach their chronically ill neighbors about improving their health.

Simultaneous determination of p-aminohippuric acid, acetyl-p-aminohippuric acid and iothalamate in human plasma and urine by high-performance liquid chromatography

A sensitive and specific high-performance liquid chromatographic assay was developed for the simultaneous determination of p-aminohippuric acid (PAH), acetyl-p-aminohippuric acid (aPAH), and iothalamate in human plasma and urine. Plasma samples were prepared by protein precipitation with acetonitrile followed by evaporation, reconstitution in mobile phase, and injection onto a C18 reversed-phase column. Urine samples were diluted with 3 volumes of mobile phase prior to injection. Column effluent was monitored by UV detection at 254 nm. The lower limits of quantification in plasma were 0.5 mg/l for PAH and aPAH, and 1.0 mg/l for iothalamate. The within-day and between-day coefficients of variation in plasma and urine were < or =7.8% for all analytes. This method is well suited for renal function studies using iothalamate and PAH, whether administered as a bolus dose or by continuous infusion, to measure glomerular filtration rate and effective renal plasma flow, respectively.

Using preventive care to decrease hospital admissions of pediatric patients

A new study shows a correlation between preventive care and a drop in avoidable hospitalizations. Richard Frye, Ph.D. profiles the Maryland Access to Care program, which achieved the results, and explains how it helped reduce pediatric hospital admissions.

Medicaid MCO members require extra attention to avoid "preventable diseases"

As more Medicaid recipients move into managed care plans, providers and payers are taking a closer look at Medicaid patients and their special needs. They're finding that interventions with a strong focus on patient education and community support are highly successful at helping Medicaid recipients avoid so-called preventable diseases.

Cefazolin as empiric therapy in hemodialysis-related infections: efficacy and blood concentrations

Concern about the increasing incidence of vancomycin-resistant organisms has tempered the enthusiasm for indiscriminate vancomycin use. Cefazolin has an antibacterial activity profile similar to vancomycin against most pathogens encountered in the hemodialysis (HD) population. We evaluated the clinical efficacy and serum concentrations that were achieved during empiric cefazolin use. Fifteen consecutive HD patients (five, conventional HD; five, high-efficiency HD; and five, high-flux HD) with suspected or documented infections warranting antibiotic intervention, including access-related, respiratory tract, urinary tract, or wound infections, were enrolled. Each patient received intravenous cefazolin (20 mg/kg actual body weight rounded to the nearest 500-mg increment [range, 1 to 2 g]) after each dialysis treatment for at least three doses. Cefazolin concentrations were obtained before and immediately after the next three consecutive dialysis treatments. Thirteen patients were evaluated for efficacy and all 15 were evaluated for toxicity and cefazolin blood concentrations. All patients showed at least a short-term (3-week) clinical resolution of infection with cefazolin treatment. No central nervous system toxicities were noted and no other adverse events were expressed by the patients during the course of cefazolin treatment. Predialysis cefazolin concentrations, as determined by high-performance liquid chromatography, were 70.2 +/- 42.7 (conventional HD), 45.6 +/- 18.9 (high-efficiency HD), and 41.6 +/- 23.9 mg/L (high-flux HD) over the three dialysis sessions. Cefazolin at doses of approximately 20 mg/kg administered post-HD appears to be a safe and effective empiric therapy and yields predialysis cefazolin concentrations of 2.5 times or greater than those considered to be the minimum inhibitory concentration breakpoint (16 mg/L) for susceptible organisms. These data support the broader use of cefazolin for empiric treatment in the HD population, allowing vancomycin to be reserved for confirmed resistant organisms.

Chloroquine modulation of specific metabolizing enzymes activities: investigation with selective five drug cocktail

AIMS

The aim of this study was to investigate whether chloroquine can inhibit drug metabolism in humans, if such inhibition is general or selective for certain enzymes and evaluate the potential for and clinical significance of any drug-drug interactions when chloroquine is co-administered with other drugs.

METHODS

The study was conducted in fourteen normal non-smoking healthy male volunteers using a cocktail of five drugs consisting of caffeine, mephenytoin, debrisoquine, chlorzoxazone and dapsone to assess activities of cytochromes P450 (CYP) 1A2, 2C19, 2D6, 2E1 and 3A4 respectively. Dapsone was also used to assess N-acetyltransferase activity. The activities were assessed at baseline, after one and seven daily doses (250 mg daily) of chloroquine and 7 and 14 days after stopping chloroquine dosing.

RESULTS

Chloroquine caused a progressive and significant decrease in CYP2D6 activity as measured by debrisoquine metabolism from first to seventh dose and the activity returned to baseline gradually over 14 days after stopping administration. There was no effect on the metabolism of any of the other probe drugs.

CONCLUSIONS

Chloroquine has been shown to be capable of inhibiting the activity of CYP2D6 in vivo in humans. This effect is selective as activities of other enzymes investigated were not affected. The effect was modest but suggests a potential for drug-drug interactions when co-administered with other drugs that are substrates for this enzyme. The clinical significance of such an interaction will depend on the therapeutic index of any drug involved.

Determinants of vancomycin clearance by continuous venovenous hemofiltration and continuous venovenous hemodialysis

The clearance of vancomycin is significantly reduced in patients with acute, as well as, chronic renal failure. Although multiple-dosage regimen adjustment techniques have been proposed for these patients, there is little quantitative data to guide the individualization of vancomycin therapy in acute renal failure patients who are receiving continuous renal replacement therapy (CRRT). To determine appropriate vancomycin dosing strategies for patients receiving continuous venovenous hemofiltration (CVVH) and continuous venovenous hemodialysis (CVVHD), we performed controlled clearance studies in five stable hemodialysis patients with three hemofilters: an acrylonitrile copolymer 0.6 m2 (AN69), polymethylmethacrylate 2.1 m2 (PMMA), and polysulfone 0.65 m2 (PS). Patients received 500 mg of vancomycin intravenously at least 12 hours before the start of the clearance study. The concentration of vancomycin in multiple plasma and dialysate/ultrafiltrate samples was determined by EMIT (Syva, Palo Alto, CA). The diffusional clearance and sieving coefficient (SC) of vancomycin were compared by a mixed-model repeated-measures analysis of variance (ANOVA) with filter and blood (Q(B)), dialysate inflow (Q(DI)), or ultrafiltration rate (Q(UF)) as the main effects and patient as a random effect. Vancomycin was moderately protein bound in these patients; free fraction ranged from 49% to 83%. The SCs of the three filters were similar and significantly correlated with the free fraction of vancomycin (P = 0.01; r2 = 0.465). Significant linear relationships were observed between the diffusional clearance of vancomycin and Q(DI) for all three filters: AN69 (slope = 0.482; r2 = 0.880); PMMA (slope = 0.853; r2 = 0.966); and PS (slope = 0.658; r2 = 0.887). The slope of this relationship for the PMMA filter was significantly greater than that of the AN69 and PS filters. The clearance of vancomycin, urea, and creatinine, however, was essentially constant at all Q(B)s for all three filters. Thus, the clearance of vancomycin was not membrane dependent during CVVH. However, during CVVHD, membrane dependence of vancomycin clearance was noted at a Q(DI) greater than 16.7 mL/min; vancomycin clearance with PMMA at a Q(DI) of 25 mL/min was 66% and 43% greater than that with the AN69 and PS filters, respectively. CVVH (62% to 262%) and CVVHD (90% to 540%) can significantly augment the clearance of vancomycin in acute renal failure patients. Dosing strategies for individualization of vancomycin therapy in patients receiving CVVH and CVVHD are proposed.

Induction of CYP2E1 activity in liver transplant patients as measured by chlorzoxazone 6-hydroxylation

OBJECTIVE

To examine the phenotypic expression of CYP2E1 in liver transplant patients, as measured by the in vivo probe chlorzoxazone, and to evaluate CYP2E1 activity over time after transplantation.

METHODS

Thirty-three stable liver transplant patients were given 250 mg chlorzoxazone within 1 year after transplantation as part of a multiprobe CYP cocktail; urine and blood were collected for 8 hours. Chlorzoxazone and 6-hydroxychlorzoxazone concentrations were determined by HPLC. Twenty-eight healthy control subjects, eight patients with moderate to severe liver disease, and four patients who had not received liver transplants were also studied for comparison. The chlorzoxazone metabolic ratio, calculated as the plasma concentration of 6-hydroxychlorzoxazone/chlorzoxazone at 4 hours after chlorzoxazone administration, was used as the phenotypic index. In a subgroup of patients and control subjects, additional blood samples were obtained to allow for the calculation of chlorzoxazone pharmacokinetic parameters by noncompartmental methods.

RESULTS

The chlorzoxazone metabolic ratio for the liver transplant patients in the first month after transplantation (mean +/- SD, 6.4 +/- 5.1) was significantly higher than that after 1 month after surgery (2.1 +/- 2.0), when the chlorzoxazone metabolic ratio was not different from control subjects (0.8 +/- 0.5). The chlorzoxazone metabolic ratios in the patients who had not received liver transplants (1.1 +/- 0.7) were equivalent to those of healthy control subjects. The maximum observed 6-hydroxychlorzoxazone plasma concentration was 3046 +/- 1848 ng/ml in seven liver transplant patients in the first month after surgery compared with 1618 +/- 320 ng/ml in 16 healthy control subjects (p < 0.05). The maximum observed concentration of chlorzoxazone, the chlorzoxazone apparent oral clearance, and the formation clearance of 6-hydroxychlorzoxazone were also significantly different between the groups.

CONCLUSIONS

We conclude that significant induction of CYP2E1, as indicated by the chlorzoxazone metabolic ratio, occurs in the first month after surgery in liver transplant patients and that drugs that are substrates for CYP2E1 may require dosage alteration during that period. Contrary to expectations, drug metabolism is not uniformly depressed after liver transplantation.

Use of chlorzoxazone as an in vivo probe of cytochrome P450 2E1: choice of dose and phenotypic trait measure

Chlorzoxazone is being developed and proposed for use as a probe to measure in vivo cytochrome P4502E1 activity, but the phenotypic trait measures that are used vary. Although the doses proposed for phenotyping range from 250 mg to 750 mg, the effect of dose on chlorzoxazone hydroxylation has not previously been evaluated. The purpose of this study was to characterize the pharmacokinetics of chlorzoxazone in normal healthy volunteers (N = 6) after single randomized oral doses of 250 mg and 750 mg. An additional 10 volunteers underwent a detailed pharmacokinetic study using the 250-mg dose to further evaluate proposed phenotypic trait measures (N = 16). Timed blood and urine samples were obtained for 10 hours for chlorzoxazone and 6-hydroxychlorzoxazone determination by HPLC. Pharmacokinetic parameter estimates were estimated using noncompartmental methods. Evaluation of phenotypic trait measures show that 6-hydroxychlorzoxazone to chlorzoxazone plasma concentration ratios at 2 to 4 hours after drug administration demonstrated the highest correlations with metabolite formation clearance (r = 0.9; P < 0.001). Urine-based parameters (e.g., total recovery) were not significantly related to formation clearance (r = 0.5; P > 0.05). Dose dependency in chlorzoxazone metabolism was shown by a 30% increase (P < 0.05) in the dose-normalized area under the concentration-time curve (AUC) of chlorzoxazone and lower incremental dose-normalized urinary recovery of 6-hydroxychlorzoxazone at early timepoints after the 750-mg dose. In addition, the plasma ratio of 6-hydroxychlorzoxazone to chlorzoxazone at 4 hours was reduced by 48% in 5 of 6 subjects after the 750-mg dose (P > 0.05). These data suggest that 6-hydroxylation was saturated at the higher dose and illustrate the importance of dose selection in phenotyping. The results of this study indicate that a chlorzoxazone dose of 250 mg should be used and that a single plasma ratio obtained 2 to 4 hours after dosing is reflective of chlorzoxazone 6-hydroxylation and thus may serve as a cytochrome P4502E1 phenotypic trait measure.

Myocardial infarction and cardiac mortality in the Bypass Angioplasty Revascularization Investigation (BARI) randomized trial

BACKGROUND

Cardiac mortality and myocardial infarction (MI) rates are used to evaluate the efficacy of coronary artery bypass grafting (CABG) and percutaneous transluminal coronary angioplasty (PTCA). We compared 5-year cardiac mortality and MI rates in 1829 patients with multivessel disease randomized to CABG or PTCA.

METHODS AND RESULTS

The 5-year cardiac mortality rate was 8.0% in patients assigned to PTCA compared with 4.9% in those assigned to CABG (relative risk [RR] of 1.55 with a 95% confidence interval [CI] of 1.07 to 2.23; P=.022). In a subgroup of 1476 nondiabetic patients, there were no significant differences between treatment groups in cardiac mortality either overall (4.6% versus 4.2%; RR= 1.04, 95% CI, 0.65 to 1.66; P=.908) or in subgroups based on symptoms, left ventricular function, number of diseased vessels, or stenotic proximal left anterior descending artery. The two treatment groups had similar event rates for the combined end point of cardiac death or MI. The RR for cardiac mortality in 264 patients who sustained an MI compared with those who did not was 5.9 (P<.001). MIs were more common after CABG during index hospitalization (P=.004), but in the PTCA group, they were more common after discharge (P<.001).

CONCLUSIONS

The Bypass Angioplasty Revascularization Investigation (BARI) trial indicates 5-year cardiac mortality in patients with multivessel disease was significantly greater after initial treatment with PTCA than with CABG. The difference was manifest in diabetic patients on drug therapy. There were no significant differences overall for the composite end point of cardiac mortality or MI between treatment groups or for cardiac mortality in nondiabetic patients regardless of symptoms, left ventricular function, number of diseased vessels, or stenotic proximal left anterior descending artery.

Debilitating reaction following the initial dose of tramadol

OBJECTIVE

To describe a debilitating reaction following a single oral dose of tramadol.

CASE SUMMARY

A 32-year-old white man with no prior medical problems, allergies, or previous medication reactions experienced ataxia, dilation of the pupils, numbness in his arms and legs, tremulousness, and dysphoria lasting approximately 4 hours following an initial tramadol dose (100 mg). The patient recovered with no sequelae.

DISCUSSION

Central nervous system (CNS) stimulation during therapy with tramadol was reported in 7% of patients in clinical trials. These reactions are usually mild and transient. This report describes a debilitating CNS-mediated reaction to an initial dose of tramadol in an otherwise healthy adult. The patient was phenotyped for CYP2D6 activity, the major metabolic pathway for tramadol elimination, and was determined to be an extensive metabolizer with very high CYP2D6 activity.

CONCLUSIONS

The exact mechanism of the adverse response is not known; however, based on phenotyping results, we suspect that it may be related to high concentrations of the active O-desmethyl metabolite of tramadol.

Validation of the five-drug "Pittsburgh cocktail" approach for assessment of selective regulation of drug-metabolizing enzymes

OBJECTIVES

To determine whether the probe drugs caffeine, chlorzoxazone, dapsone, debrisoquin (INN, debrisoquine), and mephenytoin can be simultaneously administered as a metabolic cocktail to estimate in vivo cytochrome P450 (CYP) and N-acetyltransferase enzyme activities.

METHODS

Fourteen healthy nonsmoking male volunteers (mean age +/- SD, 21.6 +/- 2.2 years) received 100 mg caffeine, 250 mg chlorzoxazone, 100 mg dapsone, 10 mg debrisoquin, and 100 mg mephenytoin individually and in four and five-drug combinations in a randomized manner using a 7 x 7 Latin square. Each drug or drug combination was given orally after an overnight fast, with a minimum 1-week washout between administrations. In each session, urine was collected from 0 to 8 hours and plasma was obtained at 4 and 8 hours after drug administration. Plasma and metabolite concentrations were used to estimate phenotypic trait measures for the efficiency of each drug's metabolism.

RESULTS

The phenotypic indexes determined for caffeine, chlorzoxazone, dapsone, debrisoquin, and mephenytoin were not significantly different when given alone than when given in combination. The median percentage change of the trait measures observed during administration of all five compounds compared with individual administration ranged from -10.7% for the 6-hydroxychlorzoxazone to chlorzoxazone plasma ratio to +2.2% for the debrisoquin recovery ratio.

CONCLUSIONS

The results of this study show that caffeine, chlorzoxazone, dapsone, debrisoquin, and mephenytoin in low doses can be simultaneously administered without metabolic interaction. This cocktail approach can thus simultaneously provide independent in vivo phenotypic measures for multiple CYP enzymes and N-acetyltransferase.