Christina L. Aquilante

Cytochrome P450 2C8 pharmacogenetics: a review of clinical studies

Cytochrome P450 (CYP) 2C8 is responsible for the oxidative metabolism of many clinically available drugs from a diverse number of drug classes (e.g., thiazolidinediones, meglitinides, NSAIDs, antimalarials and chemotherapeutic taxanes). The CYP2C8 enzyme is encoded by the CYP2C8 gene, and several common nonsynonymous polymorphisms (e.g., CYP2C8*2 and CYP2C8*3) exist in this gene. The CYP2C8*2 and *3 alleles have been associated in vitro with decreased metabolism of paclitaxel and arachidonic acid. Recently, the influence of CYP2C8 polymorphisms on substrate disposition in humans has been investigated in a number of clinical pharmacogenetic studies. Contrary to in vitro data, clinical data suggest that the CYP2C8*3 allele is associated with increased metabolism of the CYP2C8 substrates, rosiglitazone, pioglitazone and repaglinide. However, the CYP2C8*3 allele has not been associated with paclitaxel pharmacokinetics in most clinical studies. Furthermore, clinical data regarding the impact of the CYP2C8*3 allele on the disposition of NSAIDs are conflicting and no definitive conclusions can be made at this time. The purpose of this review is to highlight these clinical studies that have investigated the association between CYP2C8 polymorphisms and CYP2C8 substrate pharmacokinetics and/or pharmacodynamics in humans. In this review, CYP2C8 clinical pharmacogenetic data are provided by drug class, followed by a discussion of the future of CYP2C8 clinical pharmacogenetic research.

PharmGKB summary: very important pharmacogene information for cytochrome P450, family 2, subfamily C, polypeptide 8.

This PharmGKB summary briefly discusses the CYP2C19 gene and current understanding of its function, regulation, and pharmacogenomic relevance.

Impact of the CYP2C8 *3 polymorphism on the drug–drug interaction between gemfibrozil and pioglitazone

AIMnThe objective of this study was to determine the extent to which the CYP2C8*3 allele influences pharmacokinetic variability in the drug-drug interaction between gemfibrozil (CYP2C8 inhibitor) and pioglitazone (CYP2C8 substrate).nnnMETHODSnIn this randomized, two phase crossover study, 30 healthy Caucasian subjects were enrolled based on CYP2C8*3 genotype (n = 15, CYP2C8*1/*1; n = 15, CYP2C8*3 carriers). Subjects received a single 15 mg dose of pioglitazone or gemfibrozil 600 mg every 12 h for 4 days with a single 15 mg dose of pioglitazone administered on the morning of day 3. A 48 h pharmacokinetic study followed each pioglitazone dose and the study phases were separated by a 14 day washout period.nnnRESULTSnGemfibrozil significantly increased mean pioglitazone AUC(0,∞) by 4.3-fold (P < 0.001) and there was interindividual variability in the magnitude of this interaction (range, 1.8- to 12.1-fold). When pioglitazone was administered alone, the mean AUC(0,∞) was 29.7% lower (P = 0.01) in CYP2C8*3 carriers compared with CYP2C8*1 homozygotes. The relative change in pioglitazone plasma exposure following gemfibrozil administration was significantly influenced by CYP2C8 genotype. Specifically, CYP2C8*3 carriers had a 5.2-fold mean increase in pioglitazone AUC(0,∞) compared with a 3.3-fold mean increase in CYP2C8*1 homozygotes (P = 0.02).nnnCONCLUSIONnCYP2C8*3 is associated with decreased pioglitazone plasma exposure in vivo and significantly influences the pharmacokinetic magnitude of the gemfibrozil-pioglitazone drug-drug interaction. Additional studies are needed to evaluate the impact of CYP2C8 genetics on the pharmacokinetics of other CYP2C8-mediated drug-drug interactions.

Evaluation of sulfobutylether-β-cyclodextrin (SBECD) accumulation and voriconazole pharmacokinetics in critically ill patients undergoing continuous renal replacement therapy

IntroductionIntravenous (IV) voriconazole is not recommended in patients with creatinine clearance <50xa0ml/min to avoid potentially toxic accumulation of sulfobutylether-β-cyclodextrin (SBECD). The purpose of this study was to evaluate the pharmacokinetics of SBECD, voriconazole, and voriconazole N-oxide in critically ill patients undergoing continuous renal replacement therapy (CRRT) and to determine if CRRT removes SBECD sufficiently to allow for the use of IV voriconazole without significant risk of SBECD accumulation.MethodsThis prospective, open-label pharmacokinetic study enrolled patients >18xa0years old receiving IV voriconazole for a known or suspected invasive fungal infection while undergoing CRRT. Serial blood and effluent samples were collected on days 1, 3, 5, 7, and every 3 to 5xa0days thereafter. SBECD, voriconazole, and voriconazole N-oxide plasma and effluent concentrations were measured by liquid chromatography-tandem mass spectrometry. Pharmacokinetic, pharmacodynamic, and pharmacogenetic analyses were conducted.ResultsTen patients (meanu2009±u2009standard deviation (SD)) 53u2009±u200911xa0years old, 50% male, 81u2009±u200914xa0kg, with Acute Physiologic and Chronic Health Evaluation II (APACHE II) scores of 31.5u2009±u20093.8 were evaluated. All patients underwent continuous venovenous hemofiltration (CVVH) with a median predilution replacement fluid rate of 36 (interquartile range (IQR) 32 to 37) ml/kg/hr and total ultrafiltration rate of 38 (IQR 34 to 39) ml/kg/hr. Meanu2009±u2009SD voriconazole and SBECD dosages administered were 8.1u2009±u20092.1xa0mg/kg/day and 129u2009±u200933xa0mg/kg/day, respectively. Voriconazole plasma trough concentrations were >1xa0mg/L in all patients with CVVH accounting for only 15% of the total body clearance. CVVH accounted for 86% of the total body clearance of SBECD with the majority of the dose being recovered in the effluent. Minimal increases in dose normalized SBECD area under the concentration-time curve from 0 to 12xa0hours (AUC0-12) (4,484u2009±u20094,368 to 4,553u2009±u20092,880xa0mg*hr/L; Pu2009=u20090.97) were observed after study day 1.ConclusionsCVVH effectively removed SBECD at a rate similar to the ultrafiltration rate. Voriconazole clearance by CVVH was not clinically significant. Standard dosages of IV voriconazole can be utilized in patients undergoing CVVH without significant risk of SBECD accumulation.Trial registrationClinicalTrials.gov NCT01101386. Registered 6 April 2010.

Evaluation of the relationship between circulating omentin-1 concentrations and components of the metabolic syndrome in adults without type 2 diabetes or cardiovascular disease

BackgroundDysregulation of omentin-1, a beneficial adipokine, is thought to play a role in the development of type 2 diabetes and cardiovascular disease. The objective of this study was to evaluate the relationship between circulating omentin-1 concentrations and components of the metabolic syndrome in adults without type 2 diabetes or cardiovascular disease, and to determine if sex differences influenced the observed relationships.MethodsFasting blood samples were obtained from 93 adults, ages 30–60xa0years, without type 2 diabetes and/or cardiovascular disease. Participants were classified as having the metabolic syndrome according to American Heart Association/National Heart, Lung and Blood Institute criteria. Plasma omentin-1 concentrations were measured using a commercially-available enzyme-linked immunosorbent assay, and relationships between plasma omentin-1 and components of the metabolic syndrome were assessed in the entire study cohort, by metabolic syndrome status, and by sex.ResultsOn average, participants were 48u2009±u20098xa0years of age, 50.5% were women, 54.8% were Caucasian, and 70% had the metabolic syndrome. Plasma omentin-1 concentrations did not differ significantly between individuals with versus without the metabolic syndrome (145.7u2009±u200970 versus 157.4u2009±u200979.3xa0ng/ml, pu2009=u20090.50). However, men with the metabolic syndrome had significantly lower omentin-1 levels than men without the metabolic syndrome (129.9u2009±u200966 versus 186.3u2009±u200984.3xa0ng/ml, pu2009=u20090.03). Plasma omentin-1 concentrations were significantly correlated with HDL cholesterol in the entire study cohort (ru2009=u20090.26; pu2009=u20090.01), which was primarily driven by a correlation in men (ru2009=u20090.451, pu2009=u20090.002) and participants with the metabolic syndrome (ru2009=u20090.36; pu2009=u20090.003). Plasma omentin-1 concentrations did not differ significantly between men and women; however men with the metabolic syndrome had 20% lower plasma omentin-1 levels than women with the metabolic syndrome (pu2009=u20090.06).ConclusionThese data demonstrate that circulating omentin-1 levels are associated with HDL cholesterol, primarily in men and in the presence of the metabolic syndrome. In addition, sex appears to influence the relationship between plasma omentin-1 concentrations and components of the metabolic syndrome. Additional studies are needed to explore sexual dimorphism in circulating omentin-1 levels, and the role of omentin-1 in the metabolic syndrome.

The impact of genetic polymorphisms, diltiazem, and demographic variables on everolimus trough concentrations in lung transplant recipients

Everolimus (EVR) has inter‐individual pharmacokinetic (PK) variability and a narrow therapeutic index. The study objective was to determine whether genetic polymorphisms, co‐medications, and/or demographic variables accounted for inter‐individual variability in EVR PK in lung transplant recipients (LTxR). LTxR were genotyped for ABCB1 c.1236C>T, ABCB1 c.2677G>T/A, ABCB1 c.3435C>T, CYP3A4*1B, CYP3A5*3, CYP2C8*2/*3/*4, and pregnane X receptor (NR1I2) c.44477T>C, c.63396C>T, c.69789A>G polymorphisms. The primary outcome was the difference in dose‐adjusted EVR levels (EVR L/D) between ABCB1 diplotype groups (2 vs. 1 vs. 0 copies of the 1236C/2677G/3435C haplotype). Sixty‐five LTxR were included. There was no significant difference in EVR L/D between ABCB1 CGC diplotype groups (CGC/CGC = 2.4 ± 1.1 [n = 9] vs. CGC/XXX = 2.5 ± 1.7 [n = 36] vs. XXX/XXX = 2.7 ± 1.7 ng/mL per mg/d [n = 20]; p = 0.9). CYP3A5*3, CYP3A4*1B, CYP2C8*3/*4, and NR1I2 polymorphisms were not associated with EVR L/D. EVR L/D was 3.4 ± 1.7 in LTxR receiving diltiazem (DILT) vs. 1.8 ± 1.1 ng/mL per mg/d in LTxR not receiving DILT (p <0.001). Demographic variables, including cystic fibrosis, were not associated with EVR PK. DILT use increased EVR L/D, but selected polymorphisms in ABCB1, CYP3A5, CYP3A4, CYP2C8, and NR1I2 did not affect EVR L/D in LTxR. Genotyping LTxR for these polymorphisms is unlikely to aid clinicians in optimizing EVR therapy.

Influence of CYP2C8*2 on the Pharmacokinetics of Pioglitazone in Healthy African-American Volunteers

To determine the influence of the Cytochrome P450 (CYP) 2C8*2 polymorphism on pioglitazone pharmacokinetics in healthy African‐American volunteers.

Medication regimen complexity in ambulatory older adults with heart failure

Purpose Heart failure prevalence is increasing in older adults, and polypharmacy is a major problem in this population. We compared medication regimen complexity using the validated patient-level Medication Regimen Complexity Index (pMRCI) tool in “young-old” (60–74 years) versus “old-old” (75–89 years) patients with heart failure. We also compared pMRCI between patients with ischemic cardiomyopathy (ISCM) versus nonischemic cardiomyopathy (NISCM). Patients and methods Medication lists were retrospectively abstracted from the electronic medical records of ambulatory patients aged 60–89 years with heart failure. Medications were categorized into three types – heart failure prescription medications, other prescription medications, and over-the-counter (OTC) medications – and scored using the pMRCI tool. Results The study evaluated 145 patients (n=80 young-old, n=65 old-old, n=85 ISCM, n=60 NISCM, mean age 73±7 years, 64% men, 81% Caucasian). Mean total pMRCI scores (32.1±14.4, range 3–84) and total medication counts (13.3±4.8, range 2–30) were high for the entire cohort, of which 72% of patients were taking eleven or more total medications. Total and subtype pMRCI scores and medication counts did not differ significantly between the young-old and old-old groups, with the exception of OTC medication pMRCI score (6.2±4 young-old versus 7.8±5.8 old-old, P=0.04). With regard to heart failure etiology, total pMRCI scores and medication counts were significantly higher in patients with ISCM versus NISCM (pMRCI score 34.5±15.2 versus 28.8±12.7, P=0.009; medication count 14.1±4.9 versus 12.2±4.5, P=0.008), which was largely driven by other prescription medications. Conclusion Medication regimen complexity is high in older adults with heart failure, and differs based on heart failure etiology. Additional work is needed to address polypharmacy and to determine if medication regimen complexity influences adherence and clinical outcomes in this population.

CYP3A pharmacogenetics and tacrolimus disposition in adult heart transplant recipients

Cytochrome P450 (CYP) 3A polymorphisms are associated with variable CYP3A metabolizing enzyme activity and tacrolimus pharmacokinetics. We sought to determine the singular and combined impact of CYP3A4*22 and CYP3A5*3 variants on tacrolimus drug disposition in adult heart transplant recipients.

Pharmacodynamic effects of rosiglitazone in nondiabetic patients with metabolic syndrome.

Study Objectives. To determine the effects of the thiazolidinedione rosiglitazone on the adipocyte‐derived cytokines adiponectin (an antiinflammatory and insulin‐sensitizing cytokine; low levels have been associated with metabolic syndrome) and resistin (an inflammation mediator; high levels have been associated with metabolic syndrome) in nondiabetic patients with metabolic syndrome, and to characterize the effects of rosiglitazone on other components of the metabolic syndrome phenotype in this population.