Impact of the SLCO1B1 polymorphism on the pharmacokinetics and lipid-lowering efficacy of multiple-dose pravastatin.

BACKGROUND AND OBJECTIVE: The polymorphism of SLCO1B1 (solute carrier organic anion transporter family, member 1B1), encoding the hepatic uptake transporter organic anion transporting polypeptide 1B1, has been associated with increased pravastatin concentrations in single-dose studies. We have investigated whether this polymorphism influences the pharmacokinetics and lipid-lowering efficacy of multiple-dose pravastatin. METHODS: A prospective, parallel-group study of 16 healthy volunteers, including 8 carriers of an SLCO1B1 variant haplotype and 8 control subjects, was carried out. Pravastatin pharmacokinetics and reduction in total and low-density lipoprotein (LDL) cholesterol concentrations were analyzed after treatment with 40 mg pravastatin daily for 3 weeks. RESULTS: The mean area under the plasma concentration-time curve of pravastatin was 110% higher (305.0 +/- 149.4 ng . h/mL [mean +/- SD] versus 144.9 +/- 48.2 ng . h/mL, P = .012) and the mean peak concentration in plasma was 231% higher (174.5 +/- 98.6 ng/mL versus 52.7 +/- 22.1 ng/mL, P = .0042) in the SLCO1B1 variant haplotype group than in the control group. Pravastatin significantly reduced the concentrations of total and LDL cholesterol in both groups. The mean percentage reduction in total cholesterol concentration was 13.1% +/- 9.1% and 19.1% +/- 8.3% in the variant and control groups, respectively (P = .19; 95% confidence interval of difference between groups, -15.3% to 3.3%). The mean percentage reduction in LDL cholesterol concentration was 27.7% +/- 8.3% in the variant group and 32.3% +/- 11.2% in the control group (P = .37; 95% confidence interval for difference, -15.1% to 6.0%). CONCLUSIONS: Despite considerably higher plasma pravastatin concentrations in carriers of an SLCO1B1 variant haplotype, there was no significant difference in the lipid-lowering efficacy of pravastatin between the variant haplotype and control groups. However, this pilot study had sufficient statistical power to detect only a large difference in lipid response between the 2 groups. Further clinical studies are warranted to characterize the impact of the SLCO1B1 polymorphism on the lipid response to pravastatin.

Muscle symptoms associated with statins: a series of twenty patients.

The aim of this study was to examine the clinical profile of statin-induced myalgia in patients with no apparent predisposing factors. Patients who reported muscle complaints that limited daily functioning during statin use were prospectively identified among the patients of Kuusankoski District Hospital and its catchment area, a population of about 100,000, between January 2003 and July 2004. Twenty patients in whom the muscle complaints were probably attributable to the use of a statin were included in this series. There were no cases of severe myopathy or rhabdomyolysis, and the highest creatine kinase value observed was only about 1900 U/l. Of the 18 patients that were evaluable for creatine kinase level, 5 (28%) did not exhibit elevation of creatine kinase and 6 (33%) showed a minor increase only. Following discontinuation of the statin, resolution of symptoms and normalisation of creatine kinase occurred in 11 of the 13 patients with elevated creatine kinase value as well as muscle complaints. Statins may cause clinically important muscle symptoms without inducing a marked creatine kinase elevation.

Impact of CYP2D6 genotype on adverse effects during treatment with metoprolol: a prospective clinical study.

OBJECTIVE: Our objective was to study the impact of the cytochrome P450 (CYP) 2D6 polymorphism on the tolerability of metoprolol in a real-life primary care setting. The adverse effects studied comprised effects related to the central nervous system, cardiovascular effects, and sexual dysfunction. METHODS: Patients in whom treatment with metoprolol was considered were enrolled into this prospective, 6-week multicenter study. The dosage of metoprolol was determined on an individual basis and could be freely adjusted on clinical grounds. The indication for treatment was hypertension in about 90% of cases. Systolic and diastolic blood pressure, resting heart rate, and plasma metoprolol and alpha-hydroxymetoprolol concentrations were measured. CYP2D6 genotyping covered alleles *3 to *10 and *41 and the duplications. Possible adverse effects of metoprolol were systematically assessed over a 6-week period by means of standardized rating scales and questionnaires. RESULTS: The final study population comprised 121 evaluable patients (all white patients); among them, there were 5 ultrarapid metabolizers (UMs) (4.1%), 91 extensive metabolizers (EMs) (75%), 21 intermediate metabolizers (IMs) (17%), and 4 poor metabolizers (PMs) (3.3%). Plasma metoprolol concentrations normalized for the daily dose and metoprolol/alpha-hydroxymetoprolol ratios at steady state were markedly influenced by CYP2D6 genotype and displayed a gene-dose effect. The median of the dose-normalized metoprolol concentration was 0.0088 ng/mL, 0.047 ng/mL, 0.34 ng/mL, and 1.34 ng/mL among UMs, EMs, IMs, and PMs, respectively (P<.0001). There was no significant association between CYP2D6 genotype-derived phenotype (EMs and UMs combined versus PMs and IMs combined) and adverse effects during treatment with metoprolol. There was a tendency toward a more frequent occurrence of cold extremities in the PM plus IM group as compared with the EM plus UM group (16.0% versus 4.2%, P=.056; relative risk, 3.8 [95% confidence interval, 1.03--14.3]). CONCLUSIONS: CYP2D6 genotype-derived phenotype was not significantly associated with a propensity for adverse effects to develop during treatment with metoprolol. However, the results concerning tolerability of metoprolol in PMs were inconclusive because of the small number of PMs enrolled.

Polymorphic organic anion transporting polypeptide 1B1 is a major determinant of repaglinide pharmacokinetics.

BACKGROUND AND OBJECTIVE: A large interindividual variability exists in the plasma concentrations of repaglinide. Our aim was to investigate possible associations between the pharmacokinetics of repaglinide and single nucleotide polymorphisms (SNPs) in the genes encoding for the drug transporters organic anion transporting polypeptide 1B1 (OATP1B1) (SLCO1B1 ) and P-glycoprotein ( MDR1 , ABCB1 ) and the drug-metabolizing enzymes cytochrome P450 (CYP) 2C8 and CYP3A5. METHODS: A total of 56 healthy volunteers ingested a single 0.25-mg dose of repaglinide. Plasma repaglinide and blood glucose concentrations were measured for up to 7 hours. All subjects were genotyped for the -11187G>A and 521T>C SNPs in SLCO1B1 and the 3435C>T and 2677G>T/A SNPs in ABCB1 , as well as for the CYP2C8*3 (416G>A, 1196A>G), CYP2C8*4 (792C>G), and CYP3A5*3 (6986A>G) alleles. RESULTS: The area under the plasma concentration-time curve from time 0 to infinity [AUC(0-infinity)] and peak concentration in plasma (Cmax) of repaglinide varied 16.9-fold and 10.7-fold, respectively, between individual subjects. Multiple regression analyses indicated that the SLCO1B1 521T>C SNP and the CYP2C8*3 allele were independent predictors of the AUC(0-infinity) and Cmax of repaglinide (adjusted multiple R2 = 45% and 36%, respectively). In subjects with the SLCO1B1 521CC genotype, the AUC(0-infinity) of repaglinide was 107% and 188% higher, respectively, than in subjects with the SLCO1B1 521TC or 521TT (reference) genotype (P < .0001). In subjects with the CYP2C8*1/*3 genotype, the AUC(0-infinity) and Cmax of repaglinide were 48% and 44% lower, respectively, than in those with the CYP2C8*1/*1 genotype (P < .05). The pharmacokinetics of repaglinide was not associated with the studied ABCB1 SNPs or the CYP3A5*3 allele. The elimination half-life of repaglinide was not associated with any SNP. Only the SLCO1B1 -11187GA genotype was significantly associated with an enhanced effect of repaglinide on blood glucose. CONCLUSIONS: Genetic polymorphism in SLCO1B1 is a major determinant of interindividual variability in the pharmacokinetics of repaglinide. The effect of SLCO1B1 polymorphism on the pharmacokinetics of repaglinide may be clinically important.

CYP3A5 genotype is associated with diagnosis of hypertension in elderly patients: data from the DEBATE Study.

OBJECTIVE: The aim of this study was to address the presently controversial question of whether cytochrome P450 (CYP) 3A5 polymorphism is associated with hypertension. METHOD: We studied 373 elderly (age > or =75 years) Finnish (Caucasian) patients from the ongoing DEBATE (Drugs and Evidence Based Medicine in the Elderly) trial. The patients were classified into those with a history of hypertension (n = 229) and those without a history of hypertension (n = 144) on the basis of a detailed questionnaire on each patient's medical history and an interview. The patients were genotyped for the CYP3A5 6986A/G single nucleotide polymorphism (SNP) [CYP3A5*1/*3 alleles]. RESULTS: The proportion of individuals with the CYP3A5*1/*3 genotype, i.e. CYP3A5 expressors, was significantly higher among patients with a diagnosis of hypertension than among patients without (18.3% vs 9.0%, p = 0.016). The corresponding odds ratio was 2.26 (95% CI 1.17, 4.38). The allele and genotype frequencies for the two control SNPs, ABCB1 (MDR1) 3435C/T and SLCO1B1 521T/C, did not differ between the two groups. CONCLUSION: This work lends support to the theory that the polymorphic CYP3A5 enzyme may be involved in regulation of blood pressure. The possible role of CYP3A5 as a genetic contributor to hypertension susceptibility warrants further study.

Lipid-lowering response to statins is affected by CYP3A5 polymorphism.

Individuals expressing the polymorphic CYP3A5 enzyme might show a more than average efficiency in the metabolism of lovastatin, simvastatin and atorvastatin. We studied whether the expression of CYP3A5 is associated with an impaired lipid-lowering response to statins in 69 Caucasian patients. Lovastatin, simvastatin and atorvastatin were significantly less effective in CYP3A5 expressors than in non-expressors. The mean serum total cholesterol concentration at 1 year was 23% higher (P = 0.0014) and the mean serum low-density lipoprotein cholesterol concentration was 24% higher (P = 0.036) in subjects possessing the CYP3A5*1 allele (CYP3A5 expressors, n = 7) than in subjects homozygous for the CYP3A5*3 allele (non-expressors, n = 39). The mean percentage reduction in serum total cholesterol from baseline was significantly smaller in CYP3A5 expressors than in non-expressors (17% versus 31%, P = 0.026). No association between hypolipidemic efficacy and CYP3A5 polymorphism was observed among 23 subjects taking statins that are not dependent on CYP3A5 (fluvastatin, pravastatin). These findings suggest that CYP3A5 may be a genetic determinant of interindividual differences in response to certain statins.

Differential expression and function of CYP2C isoforms in human intestine and liver.

This study aimed to characterize the intestinal and hepatic expression and function of CYP2C enzymes in the same set of subjects. CYP2C isoform-specific quantitative reverse transcription-polymerase chain reaction assays, Western immunoblotting and marker reactions of CYP2C8, CYP2C9 and CYP2C19 activities were employed to investigate expression and activity of the CYP2C isoforms in samples of small intestine and liver obtained from 15 patients undergoing gastrectomy or pancreatoduodenectomy. The rank order for CYP2C mRNA expression in the intestine was CYP2C9 = CYP2C18 > CYP2C19 > CYP2C8, whereas that in the liver was CYP2C9 > CYP2C8 > CYP2C18 > CYP2C19. The rank order for expression of CYP2C protein in the intestine was CYP2C9 > CYP2C19 > CYP2C8 (content below limit of quantification) > CYP2C18 (not detected) and that in the liver was CYP2C9 > CYP2C8 > CYP2C19 > CYP2C18 (not detected). The CYP2C9 protein content was approximately 10-fold higher in the liver than in the intestine (P < 0.001). The CLint for the formation of D-703 from verapamil (marker of CYP2C8 activity) was 7.6-fold higher (P < 0.001) and that for the diclofenac 4'-hydroxylation (marker of CYP2C9 activity) was 6.1-fold higher (P < 0.001) in the liver than in the intestine. Apart from a borderline positive correlation (r = 0.58, P = 0.0504) between the intestinal and hepatic CLint for the diclofenac 4'-hydroxylation, no intra-individual relationships between these tissues with respect to expression or activity of different CYP2C isoforms were found. Collectively, these results show that CYP2C8, CYP2C9 and CYP2C19 are expressed as functional enzymes in the human small intestine, and further suggest that CYP2C genes are independently regulated in human intestine and liver. Although, overall, the expression and activity of CYP2C enzymes is lower in the gut than in the liver, the surface area of the proximal small intestine is large and intestinal CYP2C9 and CYP2C19 may well contribute to the first-pass metabolism of their substrate drugs.

High plasma pravastatin concentrations are associated with single nucleotide polymorphisms and haplotypes of organic anion transporting polypeptide-C (OATP-C, SLCO1B1).

This study aimed to characterize possible relationships between polymorphisms in the drug transporter genes organic anion transporting polypeptide-C (OATP-C, SLCO1B1), OATP-B (SLCO2B1), multidrug resistance-associated protein 2 (MRP2, ABCC2) and multidrug resistance transporter (MDR1, ABCB1) and the pharmacokinetics of pravastatin. We studied 41 healthy Caucasian volunteers who had previously participated in pharmacokinetic studies with pravastatin. Six volunteers had a very high pravastatin AUC value and were defined as outliers according to statistical criteria. The OATP-C gene was sequenced completely in all subjects, and they were also genotyped for selected single nucleotide polymorphisms (SNP) in the OATP-B, MDR1 and MRP2 genes. Of the six outliers, five were heterozygous for the OATP-C 521T>C (Val174Ala) SNP (allele frequency 42%) and three were heterozygous for a new SNP in the promoter region of OATP-C (-11187G>A, allele frequency 25%). Among the remaining 35 subjects, two were homozygous and six were heterozygous carriers of the 521T>C SNP (allele frequency 14%, P = 0.0384 versus outliers) and three were heterozygous carriers of the -11187G>A SNP (allele frequency 4%, P = 0.0380 versus outliers). In subjects with the -11187GA or 521TC genotype, the mean pravastatin AUC0-12 was 98% (P = 0.0061) or 106% (P = 0.0034) higher, respectively, compared to subjects with the reference genotype. These results were substantiated by haplotype analysis. In heterozygous carriers of *15B (containing the 388A>G and 521T>C variants), the mean pravastatin AUC0-12 was 93% (P = 0.024) higher compared to non-carriers and, in heterozygous carriers of *17 (containing the -11187G>A, 388A>G and 521T>C variants), it was 130% (P = 0.0053) higher compared to non-carriers. No significant associations were found between OATP-B, MRP2 or MDR1 polymorphisms and the pharmacokinetics of pravastatin. These results suggest that haplotypes are more informative in predicting the OATP-C phenotype than single SNPs.

Cytochrome P450 3A4 and P-glycoprotein expression in human small intestinal enterocytes and hepatocytes: a comparative analysis in paired tissue specimens.

OBJECTIVES: Our objectives were to determine the content of cytochrome P450 (CYP) 3A4, CYP3A5, and P-glycoprotein and to measure CYP3A4-dependent catalytic activity in paired human small intestinal and liver specimens. METHODS: Samples of duodenum or proximal jejunum and liver wedge biopsy specimens were obtained from 15 patients undergoing a gastrointestinal operation. Enterocytes were isolated from the intestinal samples. The contents of CYP3A4, CYP3A5, and P-glycoprotein and CYP3A4-mediated catalytic activities were determined in homogenized enterocyte and liver samples. RESULTS: The CYP3A4 protein content was about 3 times (P <.01) and the P-glycoprotein content about 7 times (P <.0001) higher in the enterocyte homogenates than in the liver homogenates. CYP3A5 protein was detected in all samples, but the levels were too low in most cases to allow quantification. The 2 cases with a quantifiable hepatic CYP3A5 content had the CYP3A5*1/*3 genotype; all other cases were homozygous for the CYP3A5*3 allele. No intraindividual correlations between the intestine and liver with respect to CYP3A4 content, P-glycoprotein content, or the measured catalytic activities were present. Values for the maximum rate of metabolism (V(max)) of verapamil N-dealkylation (formation of D-617) and N-demethylation (formation of norverapamil) activities correlated with the CYP3A4 protein content in both organs. CONCLUSIONS: This work demonstrated a much higher content of both CYP3A4 protein and P-glycoprotein in enterocytes isolated from human duodenal or jejunal mucosa than in paired specimens of liver tissue. These results lend support to the view that biotransformation in the gut wall substantially contributes to the overall first-pass metabolism of many CYP3A4 substrates. Furthermore, the high content of P-glycoprotein on the apical surface of enterocytes supports the theory that this efflux transporter may act in concert with CYP3A4 to limit oral drug bioavailability. Finally, these results indicate that neither CYP3A4 nor MDR1 (P-glycoprotein) is coordinately regulated in the liver and intestine.

Glyburide and glimepiride pharmacokinetics in subjects with different CYP2C9 genotypes.

OBJECTIVES: Our objective was to investigate the effects of genetic polymorphisms of cytochrome P450 (CYP) 2C9 on the pharmacokinetics of glyburide (INN, glibenclamide) and glimepiride, two widely used sulfonylurea antidiabetic drugs. METHODS: We conducted CYP2C9 genotyping for 29 healthy volunteers who had participated in our previous pharmacokinetic studies on glyburide or glimepiride. RESULTS: There were 17 subjects (59%) with the CYP2C9*1/*1 (wild-type) genotype, 8 (28%) with the CYP2C9*1/*2 genotype, 3 (10%) with the CYP2C9*1/*3 genotype, and 1 (3%) with the CYP2C9*2/*3 genotype. The pharmacokinetics of glyburide or glimepiride were not significantly changed among subjects with the CYP2C9*1/*2 genotype. However, in individuals heterozygous for the CYP2C9*3 allele, the median total area under the plasma concentration-time curve of glyburide (n = 2) was 280% (P < or = .05) and that of glimepiride (n = 3) was 267% (P < or = .01) of the respective values in subjects with the CYP2C9*1/*1 genotype (n = 5 and n = 12, respectively). Blood glucose responses to glyburide and glimepiride were not significantly affected by the CYP2C9 genotype. CONCLUSIONS: Genetic polymorphisms of CYP2C9 markedly affect the pharmacokinetics of both glyburide and glimepiride. The influence of the CYP2C9*3 variant allele on glyburide and glimepiride pharmacokinetics may be clinically significant.

Plasma concentrations of inhaled budesonide and its effects on plasma cortisol are increased by the cytochrome P4503A4 inhibitor itraconazole.

OBJECTIVE: Our objective was to examine the effects of itraconazole on the pharmacokinetics and cortisol-suppressant activity of budesonide administered by inhalation. METHODS: In a randomized, double-blind, 2-phase crossover study, 10 healthy subjects took 200 mg itraconazole or placebo orally once a day for 5 days. On day 5, 1 hour after the last dose of itraconazole or placebo, 1000 microg budesonide was administered by inhalation. Plasma budesonide and cortisol concentrations were measured up to 23 hours. RESULTS: Itraconazole increased the mean total area under the plasma concentration-time curve of inhaled budesonide 4.2-fold (range, 1.7-fold to 9.8-fold; P <.01) and the peak plasma concentration 1.6-fold (P <.01) compared with placebo. The mean terminal half-life of budesonide was prolonged from 1.6 to 6.2 hours (ie, 3.7-fold; range, 1.5-fold to 9.3-fold; P <.001) by itraconazole. The suppression of cortisol production after inhalation of budesonide was significantly increased by itraconazole as compared with placebo, as shown by a 43% reduction in the area under the plasma cortisol concentration-time curve from 0.5 to 10 hours (P <.001) and a 12% decrease in the cortisol concentration measured 23 hours after administration of budesonide, at 8 am (P <.05). CONCLUSIONS: Itraconazole markedly increased systemic exposure to inhaled budesonide, probably by inhibiting the cytochrome P4503A4-mediated metabolism of budesonide during both the first-pass and the elimination phases. This interaction resulted in enhanced systemic effects of budesonide, as shown by suppression of cortisol production. Long-term coadministration of budesonide and a potent CYP3A4 inhibitor may be associated with an increased risk of adverse effects of budesonide.

Pharmacokinetic interactions with rifampicin : clinical relevance.

The antituberculosis drug rifampicin (rifampin) induces a number of drug-metabolising enzymes, having the greatest effects on the expression of cytochrome P450 (CYP) 3A4 in the liver and in the small intestine. In addition, rifampicin induces some drug transporter proteins, such as intestinal and hepatic P-glycoprotein. Full induction of drug-metabolising enzymes is reached in about 1 week after starting rifampicin treatment and the induction dissipates in roughly 2 weeks after discontinuing rifampicin. Rifampicin has its greatest effects on the pharmacokinetics of orally administered drugs that are metabolised by CYP3A4 and/or are transported by P-glycoprotein. Thus, for example, oral midazolam, triazolam, simvastatin, verapamil and most dihydropyridine calcium channel antagonists are ineffective during rifampicin treatment. The plasma concentrations of several anti-infectives, such as the antimycotics itraconazole and ketoconazole and the HIV protease inhibitors indinavir, nelfinavir and saquinavir, are also greatly reduced by rifampicin. The use of rifampicin with these HIV protease inhibitors is contraindicated to avoid treatment failures. Rifampicin can cause acute transplant rejection in patients treated with immunosuppressive drugs, such as cyclosporin. In addition, rifampicin reduces the plasma concentrations of methadone, leading to symptoms of opioid withdrawal in most patients. Rifampicin also induces CYP2C-mediated metabolism and thus reduces the plasma concentrations of, for example, the CYP2C9 substrate (S)-warfarin and the sulfonylurea antidiabetic drugs. In addition, rifampicin can reduce the plasma concentrations of drugs that are not metabolised (e.g. digoxin) by inducing drug transporters such as P-glycoprotein. Thus, the effects of rifampicin on drug metabolism and transport are broad and of established clinical significance. Potential drug interactions should be considered whenever beginning or discontinuing rifampicin treatment. It is particularly important to remember that the concentrations of many of the other drugs used by the patient will increase when rifampicin is discontinued as the induction starts to wear off.

Characterisation of cerivastatin as a P-glycoprotein substrate: studies in P-glycoprotein-expressing cell monolayers and mdr1a/b knock-out mice.

The aim of this study was to characterise the role of the efflux transporter P-glycoprotein in the disposition of cerivastatin. We investigated directional transport characteristics of [14C]cerivastatin across cell monolayers expressing P-glycoprotein (Caco-2 and L-MDR1) and disposition of cerivastatin in mice with disrupted mdr1a and mdr1b genes. The mice were given orally 1 mg/kg cerivastatin and plasma and tissue samples for analysis of cerivastatin were obtained 10, 20, or 30 min after drug administration. Four knock-out mice and four wild-type mice were studied at each time point. In addition, the hypothesis that gemfibrozil-mediated inhibition of P-glycoprotein contributes to the interaction between gemfibrozil and cerivastatin was tested in Caco-2 cells. The apparent permeability coefficient (P(app)) value for the basal-to-apical transport of cerivastatin in Caco-2 and L-MDR1 cell monolayers was 2.4 times (P<0.001) and 3.8 times (P<0.001) as high as the apical-to-basal P(app) value respectively. The P-glycoprotein inhibitor PSC-833 (1 microM) inhibited the net basal-to-apical transport of cerivastatin in Caco-2 monolayers by 35% (P<0.01) and the MRP inhibitor MK-571 (10 microM) by 50% (P<0.01). At concentrations up to 250 microM, gemfibrozil showed no significant effects on the net transport of cerivastatin in Caco-2 cells. The concentration of cerivastatin in the brain at 30 min was 3.1 times higher in the knock-out mice than in the wild-type mice (P<0.05). The brain-to-plasma cerivastatin concentration ratio at 20 min and 30 min was 2.1 (P<0.05) and 3.6 times (P<0.05) higher respectively in the knock-out animals compared with the wild-type animals. Collectively, these results indicate that cerivastatin is a P-glycoprotein substrate, although other transporters probably contribute to cerivastatin transport in humans. As several statins are P-glycoprotein substrates, beneficial as well as adverse effects of the statins might be affected by interindividual differences in P-glycoprotein expression or function caused by, e.g., the MDR1 polymorphism.

Functional interaction of intestinal CYP3A4 and P-glycoprotein.

Intestinal CYP3A4-mediated biotransformation and active efflux of absorbed drug by P-glycoprotein are major determinants of bioavailability of orally administered drugs. The hypothesis that CYP3A4 and P-glycoprotein may act in concert to limit oral drug bioavailability is attractive from a theoretical point of view. Evidence in support of such an interplay between CYP3A4 and P-glycoprotein comes mainly from a limited number of in vitro and animal studies. Obviously, it is a challenging task to demonstrate in vivo in humans that the function of CYP3A4 and P-glycoprotein in enterocytes is complementary, and results to directly support this concept remain elusive. However, CYP3A4 and P-glycoprotein are clearly an integral part of an intestinal defence system to protect the body against harmful xenobiotics, and drugs that are substrates of both proteins often have a low bioavailability after oral administration. The functional interaction of intestinal CYP3A4 and P-glycoprotein warrants additional study. Further understanding this interplay would be potentially useful during drug development to solve bioavailability problems of new drug entities.

Influence of drug transporter polymorphisms on pravastatin pharmacokinetics in humans.

The role of drug transporters in pravastatin disposition is underlined by the fact that pravastatin does not undergo significant cytochrome P-450 (CYP)-mediated biotransformation. The organic anion transporting polypeptide 1B1 (OATP1B1), encoded by SLCO1B1, and multidrug resistance-associated protein 2 [MRP2 (ABCC2)], are thought to be the major transporters involved in the pharmacokinetics of pravastatin in humans. Other transporters that may play a role include OATP2B1, organic anion transporter 3 (OAT3), bile salt export pump (BSEP), and the breast cancer resistance protein (BCRP). OATP1B1 and MRP2 mediate the hepatic uptake and biliary excretion of pravastatin, respectively. The SLCO1B1 and ABCC2 polymorphisms probably contribute to the high interindividual variability in pravastatin disposition. Recent small studies have characterized the impact of the SLCO1B1 polymorphism on pravastatin in humans, and especially the c.521T>C single-nucleotide polymorphism (SNP) seems to be an important determinant of pravastatin pharmacokinetics. Pravastatin plasma concentrations may be up to 100% higher in subjects carrying the c.521C variant, as found in the *5, *15, *16, and *17 haplotypes, reflecting diminished OATP1B1-mediated uptake into the major site of pravastatin elimination, the liver. The SLCO1B1 polymorphism seems to have a similar impact on the pharmacokinetics of single- and multiple-dose pravastatin. Overall, 2-5% of individuals in various populations may be expected to show markedly elevated plasma pravastatin concentrations due to the SLCO1B1 polymorphism. Of note, the impact of the SLCO1B1 polymorphism on statins may be dependent on ethnicity. Although individuals with a diminished hepatic uptake of pravastatin might be expected to show reduced cholesterol-lowering efficacy due to lower intracellular pravastatin concentrations, there is preliminary evidence to suggest that the SLCO1B1 polymorphism is not a major determinant of non-response to pravastatin. The possible consequences of drug transporter polymorphisms, especially the SLCO1B1 and ABCC2 polymorphisms, for the lipid-lowering efficacy and tolerability of pravastatin in various ethnic groups warrant further study.

Effect of SLCO1B1 polymorphism on induction of CYP3A4 by rifampicin.

Rifampicin (rifampin) is a potent inducer of cytochrome P450 (CYP) 3A4. It was recently identified as a substrate of the polymorphic organic anion transporting polypeptide 1B1 (OATP1B1) expressed on the sinusoidal membrane of human hepatocytes. The present study aimed to investigate the possible association of single nucleotide polymorphisms (SNP) in the SLCO1B1 gene encoding for OATP1B1 with the inducing effect of rifampicin on hepatic CYP3A4. A total of 38 healthy volunteers who had participated in drug interaction studies with rifampicin were genotyped for the g. - 11187G > A and c.521T > C SNPs in SLCO1B1, c.3435C > T SNP in ABCB1 and g.6986A > G SNP in CYP3A5. The plasma concentration of 4beta-hydroxycholesterol, an endogenous marker of CYP3A4 activity, was measured before and after administration of 600 mg rifampicin once daily for 9-11 days. Treatment with rifampicin significantly increased the mean +/- SD plasma concentration of 4beta-hydroxycholesterol from 55.2 +/- 17.9 ng/ml to 120.9 +/- 32.0 ng/ml (P < 0.001). A large intersubject variability existed in the induction of CYP3A4 by rifampicin, but no associations were observed between the variability in induction and any of the polymorphisms studied. These data suggest that SLCO1B1 polymorphism does not affect the extent of induction of hepatic CYP3A4 by rifampicin, probably because other uptake transporters, such as OATP1B3, can compensate for reduced uptake of rifampicin by OATP1B1. However, the present study had sufficient power to detect only a considerably smaller rifampicin-induced increase in 4beta-hydroxycholesterol in carriers of the SLCO1B1 c.521C allele compared to subjects with the reference genotype.

Cardiovascular effects of (R)- and (S)-verapamil and racemic verapamil in humans: a placebo-controlled study.

OBJECTIVE: To characterise the comparative potency of optically pure (R)- and (S)-verapamil as regards negative dromotropic effects on atrioventricular (AV) node conduction and to compare the hemodynamic effects of single doses of the enantiomers in healthy volunteers. METHODS: Eight healthy volunteers received a single oral dose of 120 mg (S)-verapamil, 480 mg (R)-verapamil, 240 mg racemic verapamil (rac-verapamil) or placebo on 4 separate occasions. Serum concentrations of (R)- and (S)-verapamil were measured up to 24 h. Cardiovascular effects were assessed by electrocardiography, measurement of blood pressure and transthoracic impedance cardiography (cardiac output and total peripheral resistance). The comparative potency of (R)- and (S)-verapamil with regard to prolongation of the PR interval in the surface ECG was estimated by use of the areas under the effect-time and serum concentration-time curves and linear regression analyses of per cent change in PR interval from baseline versus the logarithm of serum (R)- or (S)-verapamil concentration. RESULTS: The PR interval was significantly prolonged after all verapamil treatments as compared with placebo. (S)-verapamil was 20.6-21.8 times more potent than (R)-verapamil with regard to negative dromotropic effects. (R)-verapamil caused a significantly greater maximum reduction in the mean arterial pressure (MAP) than placebo [15.9+/-6.8 versus 8.7+/-3.2 mmHg (mean+/-SD); 95% CI on the difference, 0.79-13.7 mmHg; p<0.05], whereas MAP was not affected by the other verapamil treatments. No significant changes were observed in heart rate, cardiac output and total peripheral resistance after any verapamil treatment as compared with placebo. CONCLUSIONS: (S)-verapamil was about 20 times more potent than (R)-verapamil with regard to negative dromotropic effects on AV node conduction. (R)-verapamil but not (S)-verapamil significantly reduced the MAP as compared with placebo.

Pharmacokinetics and response to pravastatin in paediatric patients with familial hypercholesterolaemia and in paediatric cardiac transplant recipients in relation to polymorphisms of the SLCO1B1 and ABCB1 genes.

AIMS: Our aim was to investigate associations between the single nucleotide polymorphisms (SNPs) in the SLCO1B1 (encoding OATP1B1) and ABCB1 (encoding P-glycoprotein) genes with the pharmacokinetics and efficacy of pravastatin in children with heterozygous familial hypercholesterolaemia (HeFH) and in paediatric cardiac transplant recipients. METHODS: Twenty children with HeFH (aged 4.9-15.6 years) and 12 cardiac transplant recipients (aged 4.4-18.7 years and receiving triple immunosuppressive medication) who had participated in previous pharmacokinetic and pharmacodynamic studies with pravastatin were genotyped for the -11187G > A and 521T > C SNPs in the SLCO1B1 gene and for the 2677G > T/A and 3435C > T SNPs in the ABCB1 gene. RESULTS: Two HeFH patients with the -11187GA genotype had a 81% lower peak plasma pravastatin concentration (Cmax) (difference in means -13.9 ng ml(-1), 95% CI -21.1, -6.7; P < 0.001) and a 74% smaller area under the plasma concentration-time curve (AUC0, infinity) (-25.3 ng ml(-1) h, 95% CI -35.6, -15.0; P < 0.0001) and significantly greater increase in high density lipoprotein (HDL) cholesterol after 2 months treatment with pravastatin than patients with the reference genotype. No significant differences were seen in the pharmacokinetics or effects of pravastatin between HeFH patients with the SLCO1B1 521TC and 521TT genotypes. The cardiac transplant recipients with the SLCO1B1 521TC genotype (n = 3) had a 46% lower Cmax (-67.7 ng ml(-1), 95% CI -135.7, 0.3; P = 0.055) and 62% lower AUC(0,24 h) (-228.5 ng ml(-1) h, 95% CI -402.7, -54.3; P = 0.016) and a shorter half-life (t1/2) (0.9 +/- 0.1 vs. 1.3 +/- 0.4 h, P = 0.015) of pravastatin than those with the reference genotype. Decreases in total and low-density lipoprotein cholesterol by pravastatin were significantly smaller, and the increase in HDL-cholesterol was greater in the transplant recipients with the 521TC genotype compared with patients with the 521TT reference genotype. CONCLUSIONS: In children with HeFH and in paediatric cardiac transplant recipients receiving immunosuppressive medication, the -11187G > A and SLCO1B1 521T > C SNPs were associated with decreased plasma concentrations of pravastatin. These differences are opposite to those seen previously in healthy adults. The mechanisms underlying these phenomena are unclear and warrant further study.