SLCO1B1 polymorphism markedly affects the pharmacokinetics of simvastatin acid

Identifying genetic risk factors for serious adverse drug reactions: current progress and challenges

Serious adverse drug reactions (SADRs) are a major cause of morbidity and mortality worldwide. Some SADRs may be predictable, based upon a drug's pharmacodynamic and pharmacokinetic properties. Many, however, appear to be idiosyncratic. Genetic factors may underlie susceptibility to SADRs and the identification of predisposing genotypes may improve patient management through the prospective selection of appropriate candidates. Here we discuss three specific SADRs with an emphasis on genetic risk factors. These SADRs, selected based on wide-sweeping clinical interest, are drug-induced liver injury, statin-induced myotoxicity and drug-induced long QT and torsades de pointes. Key challenges for the discovery of predictive risk alleles for these SADRs are also considered.

Simvastatin: present and future perspectives

Simvastatin is lipophilic statin with a short half-life that is primarily metabolized by CYP450 3A4. At doses of 5 - 80 mg, simvastatin lowers LDL cholesterol by 25 - 50%. Simvastatin has been shown to reduce the risk of cardiovascular disease by 35% and overall mortality by up to 30% over 5 years. The recommended starting dose of simvastatin 40 mg is approved as a lipid-lowering agent and for all high-risk patients, including those with cardiovascular disease and diabetes, regardless of the baseline LDL level. Simvastatin dose should be adjusted in those receiving CYP3A4 inhibitors, gemfibrozil, or ciclosporin, amiodarone, or in those with severe renal insufficiency. Coformulation of simvastatin with ezetimibe is now available, and coformulation with extended release niacin is under development.

Pharmacogenomics of statin response

PURPOSE OF REVIEW

Although statin therapy has been shown to reduce substantially the risk for cardiovascular disease in multiple patient subgroups, there is wide inter-individual variation in statin efficacy, in terms of both plasma lipoprotein response and clinical outcome.

RECENT FINDINGS

A number of studies have reported that polymorphisms in genes affecting statin pharmacodynamics and pharmacokinetics are associated with measures of statin efficacy, but the magnitude of variation in statin response that could be explained by these associations is small. Genome-wide association studies may yield a more comprehensive set of markers for predicting statin efficacy and muscle toxicity. For the results of these analyses to have clinical value, however, there remains a need to replicate findings in multiple populations, to connect effects on LDL and other biomarkers with clinical outcomes, and to determine whether the associations apply to each individual statin.

SUMMARY

Satisfying these requirements for clinical applicability will be challenging, but discovery of specific genotypes that influence statin efficacy and characterization of their functional effects in cellular or animal model systems may enhance our understanding of determinants of cardiovascular disease risk. They may also allow us to identify pathways that may be targeted to yield effective prevention and treatment.

No significant effect of SLCO1B1 polymorphism on the pharmacokinetics of rosiglitazone and pioglitazone

AIMS

To examine possible effects of polymorphism in the SLCO1B1 gene, encoding the hepatic uptake transporter organic anion transporting polypeptide (OATP) 1B1, on the pharmacokinetics of rosiglitazone and pioglitazone in a prospective genotype panel study.

METHODS

Sixteen healthy volunteers with the homozygous SLCO1B1 c.521TT genotype (controls), 12 with the heterozygous c.521TC genotype and four with the homozygous c.521CC genotype ingested a single 4-mg dose of rosiglitazone and a single 15-mg dose of pioglitazone in a cross-over study with a wash-out period of at least 1 week.

RESULTS

SLCO1B1 polymorphism had no statistically significant effect on any of the pharmacokinetic variables of rosiglitazone, pioglitazone or their metabolites. The mean +/- SD area under the plasma rosiglitazone concentration-time curve from time 0 to infinity (AUC(0-infinity)) was 2024 +/- 561 ng ml(-1) h in the c.521TT subjects, 1763 +/- 288 ng ml(-1) h in the c.521TC subjects (geometric mean ratio c.521TC/c.521TT 0.89; 95% confidence interval 0.72, 1.11) and 1729 +/- 346 ng ml(-1) h in the c.521CC subjects (c.521CC/c.521TT 0.87; 0.63, 1.20). The AUC(0-infinity) of pioglitazone averaged 6244 +/- 1909 ng ml(-1) h in the c.521TT subjects, 5123 +/- 1165 ng ml(-1) h in the c.521TC subjects (c.521TC/c.521TT 0.83; 0.65, 1.06) and 4851 +/- 1123 ng ml(-1) h in the c.521CC subjects (c.521CC/c.521TT 0.79; 0.55, 1.14). There was a significant correlation between the AUC(0-infinity) of rosiglitazone and pioglitazone (r = 0.717, P < 0.001).

CONCLUSIONS

The SLCO1B1 c.521T-->C SNP does not affect the pharmacokinetics of rosiglitazone or pioglitazone, indicating that OATP1B1 plays no significant role in the disposition of these drugs.

Different effects of SLCO1B1 polymorphism on the pharmacokinetics of atorvastatin and rosuvastatin

Thirty-two healthy volunteers with different SLCO1B1 genotypes ingested a 20 mg dose of atorvastatin and 10 mg dose of rosuvastatin with a washout period of 1 week. Subjects with the SLCO1B1 c.521CC genotype (n=4) had a 144% (P<0.001) or 61% (P=0.049) greater mean area under the plasma atorvastatin concentration-time curve from 0 to 48 h (AUC(0-48 h)) than those with the c.521TT (n=16) or c.521TC (n=12) genotype, respectively. The AUC(0-48 h) of 2-hydroxyatorvastatin was 100% greater in subjects with the c.521CC genotype than in those with the c.521TT genotype (P=0.018). Rosuvastatin AUC(0-48 h) and peak plasma concentration (Cmax) were 65% (P=0.002) and 79% (P=0.003) higher in subjects with the c.521CC genotype than in those with the c.521TT genotype. These results indicate that, unexpectedly, SLCO1B1 polymorphism has a larger effect on the AUC of atorvastatin than on the more hydrophilic rosuvastatin.

SLCO1B1 (OATP1B1, an uptake transporter) and ABCG2 (BCRP, an efflux transporter) variant alleles and pharmacokinetics of pitavastatin in healthy volunteers

To investigate the contribution of genetic polymorphisms of SLCO1B1 and ABCG2 to the pharmacokinetics of a dual substrate, pitavastatin, 2 mg of pitavastatin was administered to 38 healthy volunteers and pharmacokinetic parameters were compared among the following groups: 421C/C(*)1b/(*)1b (group 1), 421C/C(*)1b/(*)15 (group 2), 421C/C(*)15/(*)15 and 421C/A(*)15/(*)15 (group 3), 421C/A(*)1b/(*)1b (group 4), 421A/A(*)1b/(*)1b (group 5), and 421C/A(*)1b/(*)15 (group 6). In SLCO1B1, pitavastatin area under plasma concentration-time curve from 0 to 24 h (AUC(0-24)) for groups 1, 2, and 3 was 81.1+/-18.1, 144+/-32, and 250+/-57 ng h/ml, respectively, with significant differences among all three groups. In contrast to SLCO1B1, AUC(0-24) in groups 1, 4, and 5 was 81.1+/-18.1, 96.7+/-35.4, and 78.2+/-8.2 ng h/ml, respectively. Although the SLCO1B1 polymorphism was found to have a significant effect on the pharmacokinetics of pitavastatin, a nonsynonymous ABCG2 variant, 421C>A, did not appear to be associated with the altered pharmacokinetics of pitavastatin.

The influence of macrolide antibiotics on the uptake of organic anions and drugs mediated by OATP1B1 and OATP1B3

Macrolides may cause severe drug interactions due to the inhibition of metabolizing enzymes. Transporter-mediated uptake of drugs into cells [e.g., by members of the human organic anion transporting polypeptide (OATP) family] is a determinant of drug disposition and a prerequisite for subsequent metabolism. However whether macrolides are also inhibitors of uptake transporters, thereby providing an additional mechanism of drug interactions, has not been systematically studied. The human OATP family members OATP1B1 and OATP1B3 mediate the uptake of endogenous substances and drugs such as antibiotics and HMG-CoA reductase inhibitors (statins) into hepatocytes. In this study we investigated the potential role of these uptake transporters on macrolide-induced drug interactions. By using sulfobromophthalein (BSP) and the HMG-CoA reductase inhibitor pravastatin as substrates, the effects of the macrolides azithromycin, clarithromycin, erythromycin, and roxithromycin and of the ketolide telithromycin on the OATP1B1- and OATP1B3-mediated uptake were analyzed. These experiments demonstrated that the OATP1B1- and OATP1B3-mediated uptake of BSP and pravastatin can be inhibited by increasing concentrations of all macrolides except azithromycin. The IC50 values for the inhibition of OATP1B3-mediated BSP uptake were 11 microM for telithromycin, 32 microM for clarithromycin, 34 microM for erythromycin, and 37 microM for roxithromycin. These IC50 values were lower than the IC50 values for inhibition of OATP1B1-mediated BSP uptake (96-217 microM). These macrolides also inhibited in a concentration-dependent manner the OATP1B1- and OATP1B3-mediated uptake of pravastatin. In summary, these results indicate that alterations of uptake transporter function by certain macrolides/ketolides have to be considered as a potential additional mechanism underlying drug-drug interactions.