Genome-wide association study identifies the common variants in CYP3A4 and CYP3A5 responsible for variation in tacrolimus trough concentration in Caucasian kidney transplant recipients

The immunosuppressant tacrolimus (TAC) is metabolized by both cytochrome P450 3A4 (CYP3A4) and CYP3A5 enzymes. It is common for European Americans (EA) to carry two CYP3A5 loss-of-function (LoF) variants that profoundly reduces TAC metabolism. Despite having two LoF alleles, there is still considerable variability in TAC troughs and identifying additional variants in genes outside of the CYP3A5 gene could provide insight into this variability. We analyzed TAC trough concentrations in 1345 adult EA recipients with two CYP3A5 LoF alleles in a genome-wide association study. Only CYP3A4*22 was identified and no additional variants were genome-wide significant. Additional high allele frequency genetic variants with strong genetic effects associated with TAC trough variability are unlikely to be associated with TAC variation in the EA population. These data suggest that low allele frequency variants, identified by DNA sequencing, should be evaluated and may identify additional variants that contribute to TAC pharmacokinetic variability.

Genomewide Association Study of Tacrolimus Concentrations in African American Kidney Transplant Recipients Identifies Multiple CYP3A5 Alleles

We previously reported that tacrolimus (TAC) trough blood concentrations for African American (AA) kidney allograft recipients were lower than those observed in white patients. Subtherapeutic TAC troughs may be associated with acute rejection (AR) and AR-associated allograft failure. This variation in TAC troughs is due, in part, to differences in the frequency of the cytochrome P450 CYP3A5*3 allele (rs776746, expresses nonfunctional enzyme) between white and AA recipients; however, even after accounting for this variant, variability in AA-associated troughs is significant. We conducted a genomewide association study of TAC troughs in AA kidney allograft recipients to search for additional genetic variation. We identified two additional CYP3A5 variants in AA recipients independently associated with TAC troughs: CYP3A5*6 (rs10264272) and CYP3A5*7 (rs41303343). All three variants and clinical factors account for 53.9% of the observed variance in troughs, with 19.8% of the variance coming from demographic and clinical factors including recipient age, glomerular filtration rate, anticytomegalovirus drug use, simultaneous pancreas-kidney transplant and antibody induction. There was no evidence of common genetic variants in AA recipients significantly influencing TAC troughs aside from the CYP3A gene. These results reveal that additional and possibly rare functional variants exist that account for the additional variation.

Genotype-guided tacrolimus dosing in African-American kidney transplant recipients

Tacrolimus is dependent on CYP3A5 enzyme for metabolism. Expression of the CYP3A5 enzyme is controlled by several alleles including CYP3A5*1, CYP3A5*3, CYP3A5*6 and CYP3A5*7. African Americans (AAs) have on average higher tacrolimus dose requirements than Caucasians; however, some have requirements similar to Caucasians. Studies in AAs have primarily evaluated the CYP3A5*3 variant; however, there are other common nonfunctional variants in AAs (CYP3A5*6 and CYP3A5*7) that do not occur in Caucasians. These variants are associated with lower dose requirements and may explain why some AAs are metabolically similar to Caucasians. We created a tacrolimus clearance model in 354 AAs using a development and validation cohort. Time after transplant, steroid and antiviral use, age and CYP3A5*1, *3, *6 and *7 alleles were significant toward clearance. This study is the first to develop an AA-specific genotype-guided tacrolimus dosing model to personalize therapy.

Activated Water Desorption from Poly(methylvinylidene cyanide)

We have investigated water desorption from the polymer poly(methylvinylidene cyanide). The angle resolved thermal desorption spectra show large deviations from the cosn theta distribution for water desorption from poly(methylvinylidene cyanide) indicative of an activated desorption process. The Arrhenius plots obtained from Polanyi-Wigner analysis of the thermal desorption data suggest that a two-state model of desorption applies, while theory suggests that lattice strain in the polymer plays a key role in the thermal desorption of water.

Water Absorption and Desorption from the Dipole Ordered Polymer Poly(methylvinylidene cyanide)

From thermal desorption studies, we find evidence that absorbed water in the bulk of poly(methylvinylidene cyanide) is more weakly bound than is the case for copolymer films of poly(vinylidenefluoride-trifluoroethylene). Ultraviolet laser enhanced thermal desorption of absorbed water exhibits little light polarization dependence for poly(methylvinylidene cyanide) in contrast to absorbed water in copolymer films of poly(vinylidenefluoride-trifluoroethylene). The implications of these differences are discussed.

Evidence for an Influence of Local Dipole Excitations in Thermal Desorption

Ferroelectric crystalline copolymer films of vinylidene fluoride with trifluoroethylene (70%:30%) strongly interact with the dipoles of adsorbed and absorbed water molecules. This interaction can be probed with laser-assisted thermal desorption techniques. The UV light enhancement of water desorption is strongly light polarization dependent. The electronic structure of the ferroelectric copolymer films of vinylidene fluoride with trifluoroethylene films is locally altered with incident UV radiation suggesting metastable excited states that may involve dipole reorientation.

Water adsorption on and desorption from crystalline copolymers of vinylidene fluoride with trifluoroethylene

Water adsorption and absorption on crystalline polyvinylidene fluoride with 30% trifluoroethylene, P(VDF-TrFE, 70:30), was examined by thermal desorption spectroscopy. Two distinctly different water adsorption sites are identified: one adsorbed species that resembles ice and another species that interacts more strongly with the polymer thin film. The existence of the latter species is consistent with X-ray diffraction studies of water absorbed into the bulk of copolymers of polyvinylidene fluoride with trifluoroethylene crystalline thin films. There are strong steric effects observed in the angle-resolved thermal desorption that may be a result of the large polymer thin film surface dipoles.

The elimination of the influence of ambient environmental effects on the structure of `inert' polymers

The construction and use of a vacuum chamber suitable for conventional X-ray diffraction has revealed the influence of the ambient environment, including moisture, on the bulk structure of very thin polymer films. It is concluded that studies of thin film organic systems, even those thought not to be perturbed by ambient water vapor and other contaminants, may benefit from undertaking some studies in such small sample vacuum chambers.

Cytochrome P450 isozymes 3A4 and 2B6 are involved in the in vitro human metabolism of thiotepa to TEPA

PURPOSE

To establish the cytochrome P450 (CYP) isozymes involved in the metabolism of the alkylating agent, thiotepa, to the pharmacologically active metabolite, TEPA.

METHODS

In vitro chemical inhibition studies were conducted by incubating thiotepa and pooled human hepatic microsomes in the presence of known inhibitors to CYP1A2, CYP2A6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4. Studies were also performed with cloned, expressed CYP3A4, CYP2A6, CYP2E1 and CYP2B6 microsomes, and anti-CYP2B6 monoclonal antibody.

RESULTS

Known CYP3A4 inhibitors reduced TEPA production. Inhibition with CYP2E1 inhibitors was inconsistent. All other inhibitors produced little or no change in TEPA formation. Cloned, expressed CYP2B6 and CYP3A4 microsomes catalyzed TEPA formation, whereas CYP2A6 and CYP2E1 did not. Incubation of thiotepa with anti-CYP2B6 antibody and cloned, expressed CYP2B6 microsomes resulted in reductions in the formation of TEPA, but no change in TEPA formation occurred in human liver microsomes.

CONCLUSIONS

Thiotepa is metabolized in human liver microsomes by CYP3A4 (major) and CYP2B6 (minor). There is a potential for CYP-mediated drug interactions with thiotepa. Pharmacokinetic variability of thiotepa may be related to expression of hepatic CYP isozymes.

Atraumatic palmar midcarpal dislocation in a skeletally immature adolescent with hemiatrophy

We report a late presentation of a palmar midcarpal dislocation in an adolescent female with open growth plates who had no history of antecedent wrist injury. Midcarpal arthrodesis improved function and eliminated progressive pain.

Gentamicin and tobramycin pharmacokinetics in pediatric bone marrow transplant patients

OBJECTIVE

To describe the pharmacokinetic parameters of gentamicin and tobramycin in pediatric bone marrow transplant patients.

DESIGN

Retrospective medical record review.

SETTING

Pediatric bone marrow transplant unit in a university teaching hospital.

MAIN OUTCOME MEASURES

Pharmacokinetic parameters (apparent volume of distribution [Vd] in L/kg, half-life [t1/2] in h, elimination rate constant [ke] in h-1, clearance [Cl] in mL/min/1.73 m2 and mL/min/kg) calculated from serum concentrations.

PATIENTS

Thirty-three patients aged 15 years or less who underwent bone marrow transplant and received gentamicin or tobramycin.

RESULTS

Mean pharmacokinetic parameters were Vd 0.32 +/- 0.07 L/kg, t1/2 2.32 +/- 0.65 h, Cl 1.71 +/- 0.53 mL/min/kg, and Cl 86.2 +/- 24.5 mL/min/1.73 m2. Factors such as disease state, type of marrow graft, gender, or exposure to cyclosporine had no significant effect on pharmacokinetic parameters. Linear regression indicated a weak relationship between serum creatinine (SCr) and Cl in mL/min/kg (r = 0.59), but no relationship was found between SCr and Cl in mL/min/1.73 m2, between age and apparent Vd, or between SCr and apparent Vd. Models for estimating Cl and Ke developed by multiple regression were somewhat predictive (r = 0.7). Required calculated maintenance dosages to obtain therapeutic concentrations were 8, 7, and 6 mg/kg/d in children 6 or younger, 7-12, and 13-15 years, respectively.

CONCLUSIONS

The mean Cl and apparent Vd for all ages are similar to those reported in pediatric oncology patients who had not undergone marrow transplantation. Children 6 years or younger had lower than expected Cls and larger apparent Vds than did the older children. Dosages estimated to be necessary to achieve therapeutic concentrations were 6-8 mg/kg/d.

Isradipine therapy in hypertensive pediatric patients

OBJECTIVE

To evaluate the dosage and effectiveness of isradipine to control acute or chronic hypertension in pediatric patients.

DESIGN

Retrospective medical record review.

SETTING

University teaching hospital.

PARTICIPANTS

Hospitalized pediatric patients aged 1 day to 16 years with hypertension treated with isradipine between January 1994 and March 1996.

MEASURES

Patient age, gender, weight, disease states, current medications, isradipine dosage and formulation, pre- and postsystolic, and pre- and postdiastolic blood pressure measurements with each dose of isradipine.

RESULTS

Fifty-three patients with a mean age of 5.8 +/- 4.0 years were evaluated. A mean change in the blood pressure measurements taken before the first dose of isradipine compared with the values recorded after the last dose or at discharge for all patients was -11.8% +/- 12.5% and -17.4% +/- 19.6%, respectively, for systolic and diastolic pressure. The mean dosage of isradipine in 46 patients who received regularly scheduled doses was 0.38 +/- 0.22 mg/kg/d. Patients who demonstrated a response received a mean dosage of 0.40 +/- 0.20 mg/kg/d. The total daily dosage was administered in one dose for 1 patient, two doses for 15 patients, three doses for 27 patients, and four doses for 3 patients.

CONCLUSIONS

Isradipine was an effective antihypertensive agent to reduce the systolic and/or diastolic blood pressure 10% or more compared with pretreatment measurements in 43 (81%) of 53 pediatric patients. The mean dosage was 0.38 +/- 0.22 mg/kg/d, most frequently administered in two or three equally divided doses, which is higher than the normal recommended dosage for adults.

Stability of tacrolimus in an extemporaneously compounded oral liquid

The stability of tacrolimus in an extemporaneously compounded oral liquid formulation was studied. A suspension was prepared by mixing the contents of commercially available 5-mg capsules of tacrolimus with equal amounts of Ora-Plus and Simple Syrup, NF, to make a final volume of 60 mL. The final concentration of tacrolimus in the suspension was 0.5 mg/mL. Six identical suspensions were prepared, placed in three glass and three plastic amber prescription bottles, and stored at room temperature (24-26 degrees C). Immediately after preparation and at 7, 15, 30, 45, and 56 days, samples were removed and assayed in duplicate by stability-indicating high-performance liquid chromatography. At least 98% of the initial tacrolimus concentrations remained in all suspensions throughout the study period. Color, order, and pH did not change appreciably over the study period. Tacrolimus 0.5 mg/mL compounded extemporaneously in equal amounts of Ora-Plus and Simple Syrup, NF, was stable at 24-26 degrees C for at least 56 days in both glass and plastic amber prescription bottles.

Sterility of filgrastim (G-CSF) in syringes

OBJECTIVE

To determine if the sterility of filgrastim (G-CSF) is maintained for up to 7 days when aseptically transferred from the vial to tuberculin syringes in a laminar air flow environment.

DESIGN

The study was conducted in two phases: a validation and an experimental phase. The method was validated by inoculating samples of sterile filgrastim solution with common bacterial and fungal skin contaminants. Samples were aseptically drawn into syringes in a class 100 horizontal laminar air flow hood and refrigerated. The samples were equally divided and transferred to microbiology culture media at times 0, 24 hours, 48 hours, and 7 days; incubated; and the organisms identified and quantitated. In the experimental phase, samples of filgrastim were aseptically drawn into syringes, separated into three groups, and refrigerated. At 24 hours, 48 hours, and 7 days, the samples were transferred to broth, incubated, and observed for the development of turbidity.

SETTING

A class 100 laminar air flow hood in a pediatric hospital pharmacy and a home-infusion pharmacy class 100,000 clean room.

MAIN OUTCOME MEASURES

The sterility of filgrastim in syringes was determined by comparing experimental broth culture tubes to a control tube and observing for the development of turbidity.

RESULTS

Filgrastim demonstrated the ability to support the growth of intentionally inoculated skin contaminants, both qualitatively and quantitatively. However, when aseptically transferred to syringes and refrigerated, all tested filgrastim samples remained sterile for at least 7 days.

CONCLUSIONS

Syringes of filgrastim remain sterile for 7 days when prepared in a class 100 laminar air flow hood, using aseptic technique, and stored under refrigeration. This change in practice can result in significant cost savings.

Rapidly forming apatitic mineral in an osteoblastic cell line (UMR 106-01 BSP)

This study evaluated a rapid biomineralization phenomenon exhibited by an osteoblastic cell line, UMR 106-01 BSP, when treated with either organic phosphates [beta-glycerophosphate (beta-GP), Ser-P, or Thr-P], inorganic phosphate (P(i)), or calcium. In a dose-dependent manner, these agents (2-10 mM) stimulated confluent cultures to deposit mineral in the cell layer (ED50 of approximately 4.6 mM for beta-GP (30 +/- 2 nmol Ca2+/microgram DNA) and approximately 3.8 mM (29 +/- 2 nmol Ca2+/microgram DNA) for P(i)) with a plateau in mineral formation by 20 h (ET50 approximately 12-15 h). beta-GP or P(i) treatment yielded mineral crystals having an x-ray diffraction pattern similar to normal human bone. Alizarin red-S histology demonstrated calcium mineral deposition in the extracellular matrix and what appeared to be intracellular paranuclear staining. Electron microscopy revealed small, needle-like crystals associated with fibrillar, extracellular matrix deposits and intracellular spherical structures. Mineral formation was inhibited by levamisole (ED50 approximately 250 microM), pyrophosphate (ED50 approximately 1-10 microM), actinomycin C1 (500 ng/ml), cycloheximide (50 micrograms/ml), or brefeldin A (1 microgram/ml). These results indicate that UMR 106-01 BSP cells form a bio-apatitic mineralized matrix upon addition of supplemental phosphate. This process involves alkaline phosphatase activity, ongoing RNA and protein synthesis, as well as Golgi-mediated processing and secretion.

Stability of itraconazole in an extemporaneously compounded oral liquid

The stability of itraconazole in an extemporaneously compounded oral liquid formulation was studied. A suspension was prepared from the beads contained in commercially available 100-mg itraconazole capsules and sufficient Simple Syrup, NF, to make a final volume of 60 mL. The final concentration of itraconazole in the suspension was 40 mg/mL. Three identical volumes of each suspension were prepared and stored in 2-oz capped, amber glass prescription bottles and refrigerated at 4 degrees C (range, 2-6 degrees C). Immediately after preparation and at 7, 14, 21, 28, and 35 days, samples were visually inspected and assayed in duplicate by high-performance liquid chromatography; the pH of the samples was also determined. On day 35, the mean +/- S.D. percentage of initial itraconazole concentration remaining in the three suspensions was 95.3 +/- 2.2%. The color, odor, and pH of the samples did not change appreciably over the study period. Itraconazole 40 mg/mL in an oral liquid compounded from simple syrup and beads from capsules, stored in amber glass bottles, was stable for 35 days at 4 degrees C.

Stability of ganciclovir sodium and amino acids in parenteral nutrient solutions

The stability of ganciclovir sodium and amino acids in parenteral nutrient solutions was studied. Three admixtures of ganciclovir sodium plus parenteral nutrient solution were prepared, one containing ganciclovir sodium 0.83 mg/mL, 1% amino acids, and 10% dextrose injection; one containing ganciclovir sodium 1.4 mg/mL, 2.5% amino acids, and 10% dextrose injection; and one containing ganciclovir sodium 1.4 mg/mL, 5% amino acids, and 25% dextrose injection. The solutions were visually inspected for precipitates, color change, and gas formation and were tested for pH. High-performance liquid chromatography was used to measure the concentration of ganciclovir and 16 amino acids in each admixture immediately and one, two, and three hours after preparation. There was no evidence of visual incompatibility in any of the admixtures, and pH did not vary appreciably during the study. The mean ganciclovir sodium concentration remaining was greater than 100% of the initial concentration for all the admixtures at one, two, and three hours. The mean amino acid concentration remaining in the admixtures with 2.5% or 5.0% amino acids was greater than 90% of the initial concentration for each amino acid at one, two, and three hours. The mean amino acid concentration remaining in the admixture with 1% amino acids was greater than 90% of the initial level at one and two hours. Ganciclovir sodium 0.83 mg/mL was stable for at least three hours in parenteral nutrient solution with 1% amino acids, and ganciclovir sodium 1.4 mg/mL was stable for at least three hours in admixtures with 2.5% or 5% amino acids.(ABSTRACT TRUNCATED AT 250 WORDS)

Stability and compatibility of fluconazole and aminophylline in intravenous admixtures

The stability of aminophylline and fluconazole in intravenous admixtures containing both drugs was studied. Admixtures containing aminophylline 2.0 or 1.0 mg/mL and fluconazole 1.5 or 0.5 mg/mL in 5% dextrose injection or 0.9% sodium chloride injection were prepared. Each admixture was prepared in triplicate in glass containers and kept at 24 degrees C. Immediately after preparation and at one, two, and three hours, samples were visually inspected, tested for pH, and assayed in duplicate by high-performance liquid chromatography for theophylline concentration and fluconazole concentration. More than 98% of the initial aminophylline and fluconazole concentrations remained at each test interval. There was no visible evidence of precipitation, gas formation, or color change. No appreciable change in pH occurred during the study period. Aminophylline 1.0-2.0 mg/mL and fluconazole 0.5-1.5 mg/mL admixed in 5% dextrose injection or 0.9% sodium chloride injection were stable and compatible for up to three hours at 24 degrees C.

Compatibility of cyclosporine with fat emulsion

The compatibility of cyclosporine with fat emulsion was studied. Admixtures consisted of cyclosporine injection at final drug concentrations of 0.5 and 2.0 mg/mL in 10% and 20% fat emulsion. Fat emulsion stability was determined by visual inspection, pH testing, and particle-size measurements at 0, 24, and 48 hours. Cyclosporine stability was measured with high-performance liquid chromatography at the same intervals. The admixtures were stored in glass containers at 23-25 degrees C under fluorescent light. Mean particle diameters remained relatively constant in all the admixtures throughout the study period. No particles larger than 6 microns were observed. Cyclosporine retained more than 96% of its initial concentration in all the admixtures. There were no changes in color or consistency, and pH did not vary by more than 0.11 pH unit. Cyclosporine 0.5 or 2 mg/mL was compatible with 10% or 20% fat emulsion at room temperature in glass containers for up to 48 hours.