Influence of CYP2D6*10 on the pharmacokinetics of metoprolol in healthy Korean volunteers

Background and objective: Genetic polymorphism of CYP2D6 leads to differences in pharmacokinetics of CYP2D6 substrates. The CYP2D6*10 allele is clinically important in Koreans because of its high frequency in Asians. We investigated whether the pharmacokinetics of metoprolol was altered by the presence of the CYP2D6*10 allele in Korean subjects. Methods: One hundred and seven volunteers were recruited and grouped as CYP2D6*1/*1, CYP2D6*1/*10 and CYP2D6*10/*10 according to their genotypes. Metoprolol tartrate 100 mg (Betaloc^®) was administered orally once to each subject in these three groups (n = 6, 7 and 5, respectively). The pharmacokinetic parameters of metoprolol and its metabolite, α‐hydroxymetoprolol, and the metabolic ratio for the three groups were estimated and compared. Results and discussion: The area under the plasma concentration–time curve (AUC_0→∞), the maximum plasma concentration (C_max) and the elimination half‐life (T_1/2) of metoprolol and α‐hydroxymetoprolol for the CYP2D6*10/*10 group were all significantly different from those of the CYP2D6*1/*1 group (P < 0·05). The AUC_0→∞s of metoprolol were 443·7 ± 168·1, 995·6 ± 321·4 and 2545·3 ± 632·0 ng·h/mL, and the AUC_0→∞s of α‐hydroxymetoprolol were 1232·0 ± 311·2, 1344·0 ± 288·1 and 877·4 ± 103·4 ng·h/mL for groups CYP2D6*1/*1, *1/*10 and *10/*10, respectively. The corresponding T_1/2 values of metoprolol were 2·7 ± 0·5, 3·2 ± 1·3 and 5·0 ± 1·1 h, while those of α‐hydroxymetoprolol were 5·4±1·5, 6·0 ± 1·4 and 10·5 ± 4·2 h, respectively. The metabolic ratios of the three groups were significantly different (P < 0·05). Conclusion: The CYP2D6*10 allele altered the pharmacokinetics of metoprolol in Korean subjects and is likely to affect other drugs metabolized by the CYP2D6 enzyme, similarly.     

No pharmacokinetic interactions between mycophenolic acid and tacrolimus in renal transplant recipients

Objective:  The aim of this study was to investigate drug interactions between mycophenolic acid (MPA), the active metabolite of mycophenolate mofetil (MMF) and tacrolimus, as well as the impact of CYP3A5 and UGT2B7 genetic polymorphisms on these drug interactions in 71 Japanese renal transplant recipients. Methods:  Recipients received combination immunosuppressive therapy consisting of tacrolimus and MMF. On day 28 after transplantation, the concentrations of MPA and tacrolimus were measured by high‐performance liquid chromatography and microparticle enzyme immunoassay respectively. Results:  Acute rejection was over twice more common in recipients with a total area under the observed plasma concentration‐time curve (AUC_0–12) of MPA <70 μg·h/mL than in those with higher values AUC_0–12 values (17% vs. 7%).Using this cut‐off AUC value, sensitivity was 70·6% and specificity 55·6% for acute rejection (AR). There was no change in AUC_0–12, maximum plasma concentration, trough plasma concentration, or oral clearance of tacrolimus with variation in dosage or AUC of MPA. There were also no significant differences in the MPA pharmacokinetic parameters among three tacrolimus C₀ groups: 5 ≤ C₀ < 10, 10 ≤ C₀ < 15 and 15 ≤C₀ < 20 ng/mL. Furthermore, there were no significant differences in MPA pharmacokinetic parameters between the UGT2B7*1/*1 and *1/*2 genotype groups having the CYP3A5*1 allele or the CYP3A5*3/*3 genotype. Conclusion:  Therapeutic dosages of MMF, do not significantly influence tacrolimus pharmacokinetics, and vice versa. Consequently, MPA and tacrolimus can be safely combined; however, it is necessary to monitor the plasma concentrations of each immunosuppressive agent to minimize acute rejection.     

Influence of CYP2C9 and CYP2C19 genetic polymorphisms on pharmacokinetics and pharmacodynamics of gliclazide in healthy Chinese Han volunteers

Background and objective: CYP2C9 is the major contributor to gliclazide metabolic clearance in vitro, while the pharmacokinetics of gliclazide modified release are affected mainly by CYP2C19 genetic polymorphisms in vivo. This study aims to investigate the influence of CYP2C9 and CYP2C19 genetic polymorphisms on the pharmacokinetics and pharmacodynamics of gliclazide in healthy Chinese Han volunteers. Methods: Eighteen healthy Han subjects with various combinations of CYP2C9 and CYP2C19 genotypes received 80 mg gliclazide. Plasma gliclazide concentrations were measured by a liquid chromatography–tandem mass spectrometry method for 84 h and plasma glucose and insulin levels were measured up to 15 h post‐dose. Results and discussion: There was no difference in either pharmacokinetic and or pharmacodynamic parameters of gliclazide when group A (CYP2C9*1/*1, CYP2C19 extensive metabolizers) was compared with group B (CYP2C9*1/*3, CYP2C19 *1/*1). When group C (CYP2C9*1/*1 and CYP2C19 poor metabolizers) was compared with group A, the AUC_0–∞ and C_max in group C were significantly higher [83·94 ± 40·41 vs. 16·39 ± 5·10 μg·h/mL (P = 0·000) and 1·50 ± 0·85 vs. 0·45 ± 0·18 μg/mL (P = 0·000)], and the oral clearance was significantly lower [1·17 ± 0·63 vs. 5·38 ± 1·86 L/h (P = 0·000)]. The half‐life of gliclazide was also significantly prolonged in group C subjects when compared with that of group A (33·47 ± 12·39 vs. 19·34 ± 10·45 h), but the difference was not significant (P = 0·052). The increase in serum glucose level at 11 h after dosing (ΔC_glu11) in group C was significantly higher than that of group A (?1·08 ± 0·42 vs. 0·22 ± 1·01 mmol/L, P = 0·022). The corresponding insulin levels showed no difference between the two groups. Conclusion: CYP2C9*3 was not associated with any change in the disposition of gliclazide. CYP2C19 polymorphisms appear to exert the dominant influence on the pharmacokinetics of gliclazide in healthy Chinese Han subjects, and may also affect the observed pharmacodynamics of the drug as a result.     

Relationship of CYP2D6 genetic polymorphisms and the pharmacokinetics of tramadol in Chinese volunteers

Objective: To investigate the relationship between CYP2D6 genetic polymorphisms and the pharmacokinetics of tramadol in Chinese volunteers. Method: A gene chip was established for determining CYP2D6 genotype. Forty adult healthy Chinese subjects were categorized as: group 1, CYP2D6*1/*1; group 2, CYP2D6*2/*2; group 3, CYP2D6*2/*10; group 4, CYP2D6*10/*10. After oral administration of 100 mg tramadol, plasma and urine samples were collected over a 32‐h period. Results: The main pharmacokinetic parameters of tramadol and its metabolite O‐demethyltramadol (M₁) in groups 1 and 2 were not significantly different. However, they were significantly different between groups 3 and 1, groups 4 and 1 and groups 4 and 3. Conclusion: CYP2D6*2 does not alter the pharmacokinetics of tramadol, whereas CYP2D6*10 did with homozygotes showing a more pronounced reduction than heterozygotes. The 32‐h metabolic ratio of tramadol to M₁ were (mean ± SD) 2·05 ± 1·01, 2·13 ± 0·83, 4·24 ± 2·75 and 6·85 ± 2·78, respectively, in CYP2D6*1/*1, CYP2D6*2/*2, CYP2D6*2/*10 and CYP2D6*10/*10 subjects, respectively.     

Drug interaction between St John's wort and zolpidem in healthy subjects

What is known and objective: St John’s wort (SJW, Hypericum perforatum) is one of the most commonly used herbal antidepressants for treatment of mild to moderate depression. SJW enhances CYP3A4 activity and alters the pharmacokinetics of CYP3A4 substrates. This study investigated the effect of SJW on the pharmacokinetics of zolpidem in healthy subjects. Methods: A controlled, open‐label, non‐randomized, fixed‐dose schedule design was used. Fourteen healthy male subjects received a single 10 mg oral dose of zolpidem followed by SJW administration (300 mg orally, three times a day) for 14 days; the last dose of SJW was coadministered with a single dose of zolpidem. Blood samples were obtained over a 24‐h period after zolpidem administration. Pharmacokinetic data for zolpidem alone and in combination with SJW were analysed by high‐performance liquid chromatography. Results: After repeated administration of SJW, the mean values of AUC and C_max for zolpidem significantly decreased (380·3 ± 181·4 vs. 265·4 ± 134·2 ng h/mL, P = 0·001; 83·1 ± 30·1 vs. 55·1 ± 24·8 ng/mL, P = 0·000 respectively) and the mean value of CL/F for zolpidem significantly increased (38·4 ± 31·5 vs. 56·9 ± 57·2 mL/min, P = 0·040). However, in three subjects, the AUC showed a small increase after SJW treatment. What is new and conclusion: The effect of SJW on the pharmacokinetics of zolpidem has not previously been reported. Repeated administration of SJW decreases the plasma concentration of zolpidem, probably by enhancing CYP3A4 activity. Given the wide inter‐subject variability observed, for personalized medicine, advice on the use of the combination should be individualized, based on the circumstances of the patient.     

Frequency of CYP2C9 variant alleles, including CYP2C9*13 in a Korean population and effect on glimepiride pharmacokinetics

What is known and Objective: Cytochrome P450 (CYP) 2C9 is a clinically important enzyme involved in the metabolism of many drugs commonly used in humans. Of several allelic variants known to affect the catalytic activity of the CYP2C9 enzyme, the frequencies of the CYP2C9*3 and CYP2C9*13 alleles in the Korean population have been reported as 1·1% and 0·6%, respectively. Our objective was to re‐evaluate the frequencies of CYP2C9 allelic variants in the Korean population, including the CYP2C9*13 allele by pyrosequencing, and to investigate the pharmacokinetics of glimepiride in relation to CYP2C9 genotypes, including CYP2C9*3/*3. Methods: 295 subjects were genotyped for CYP2C9*2 and CYP2C9*3 using the TaqMan procedure, and for CYP2C9*13 using pyrosequencing. These data were combined with our previously reported data to assess the CYP2C9 allele and genotype frequencies in 869 Korean subjects. Data from 24 of the 295 genotyped subjects (22 CYP2C9*1/*1 homozygotes, one CYP2C9*1/*3 heterozygote and one CYP2C9*3/*3 homozygote) who had participated in a bioequivalence study were analysed retrospectively to examine the effects of CYP2C9 genotype on glimepiride pharmacokinetics. Results: The frequencies of the CYP2C9*1/*3, *3/*3, and *1/*13 genotypes in the study population (n = 295) were 0·081 (n = 24), 0·010 (n = 3) and 0·003 (n = 1), respectively. In the 869 subjects from the combined studies, allele frequencies for CYP2C9*3 and CYP2C9*13 were 0·025 (95% CI: 0·018, 0·033) and 0·002 (95% CI: 0·000, 0·010), respectively. Relative to CYP2C9*1 homozygotes, the one CYP2C9*3 homozygous subject was found to have a higher AUC_0–∞ value (490% of the reference value) and a lower oral clearance rate (18% of the reference). What is new and Conclusion: This study is the first examination of CYP2C9*3 homozygotes in the Korean population. Our data on the one subject with this genotype suggest that CYP2C9*3/*3 momozygotes have lower clearance of glimepiride and are exposed to higher levels of the drug than wild‐type homozygotes. Although we identified a subject with the CYP2C9*13 allele using a new pyrosequencing assay, we were unfortunately unable to investigate its effects on glimepiride pharmacokinetics.     

Analysis of cytochrome P450 gene polymorphism in a lupus nephritis patient in whom tacrolimus blood concentration was markedly elevated after administration of azole antifungal agents

What is known and Objective: Both itraconazole (ITCZ) and voriconazole (VCZ) are potent inhibitors of cytochrome P450 (CYP) 3A, and their effects have been reported to be equal. However, ITCZ is metabolized by CYP3A, whereas VCZ is mainly metabolized by CYP2C9 and CYP2C19 and only partially by CYP3A. We experienced the case of a patient who showed a 5‐fold increase in trough levels of tacrolimus (FK) level after switching from ITCZ to VCZ. Our objective is to discuss the mechanism of the increase drug–drug interaction in terms of serum concentration of the azole drugs and patient pharmacogenomics. Case summary: A 53‐year‐old woman was treated with FK (1 mg/day) for lupus nephritis. Because fungal infection was suspected, she received ITCZ (100 mg/day). When ITCZ was replaced with VCZ (400 mg/day), the blood concentration of FK increased markedly from 6·1 to 34·2 ng/mL. During coadministration with FK, the levels of ITCZ and VCZ were 135·5 ng/mL and 5·5 μg/mL, respectively, with the VCZ level around 3‐fold higher than the previously reported level (1·4–1·8 μg/mL). Her CYP genotypes were CYP2C19*1/*2, CYP3A4*1/*1 and CYP3A5*3/*3. What is new and Conclusion: The patient was a CYP2C19 intermediate metabolizer (IM) and deficient in CYP3A5. The increase in plasma VCZ level appears to have been at least in part, associated with the CYP2C19 IM phenotype. One possible explanation for the marked increase in blood FK concentration was increased inhibition of CYP3A because of the impaired metabolism and subsequent increased plasma concentration of VCZ. This case shows that the severity of drug interactions may be influenced by metabolic gene polymorphism.     

Association of ABCB1, CYP3A4*18B and CYP3A5*3 genotypes with the pharmacokinetics of tacrolimus in healthy Chinese subjects: a population pharmacokinetic analysis

What is known and Objective: Tacrolimus (TAC) is metabolized mainly by the CYP3A subfamily and extruded into the intestine by P‐glycoprotein, which is encoded by the ABCB1 gene. Several studies have suggested that the CYP3A5*3 genotype influenced the pharmacokinetics (PK) of TAC. The CYP3A4*18B and CYP3A5*3 alleles are clinically important in Chinese subjects because of their relatively high frequency. The present study aimed at evaluating the effects of ABCB1 (C1236T‐G2677T/A‐C3435T), CYP3A4*18B and CYP3A5*3 genetic polymorphisms on TAC PK in healthy Chinese subjects. Methods: Data were obtained from a comparative bioavailability study of oral TAC formulations (n = 22). TAC whole blood concentrations were measured by LC‐MS/MS. Genetic polymorphisms were determined using a direct sequencing method. Nonlinear mixed‐effects modelling (NONMEM) was performed to assess the effect of genotypes and demographics on TAC PKs. Results and Discussion: Both CYP3A4*18B and CYP3A5*3 polymorphisms affected the TAC PK, whereas ABCB1 genetic polymorphisms and other demographic characteristics did not. The combined genotypes of CYP3A4*18B and CYP3A5*3 had a greater impact than either genotype alone, and they were estimated to account for 28·4% of the inter‐subject variability of apparent clearance (CL/F) by NONMEM. The CL/F in subjects with CYP3A4*1/*1‐CYP3A5*3/*3 was 10·3 L/h and was 48·5% in those not carrying CYP3A4*1/*1‐CYP3A5*3/*3. What is new and Conclusion: This is the first study to extensively explore the influence of CYP3A4*18B, CYP3A5*3 and ABCB1 genetic polymorphisms on TAC PK in healthy Chinese subjects. The results demonstrated that subjects with a combined genotype of CYP3A4*1/*1‐CYP3A5*3/*3 may require lower TAC doses to achieve target concentration levels and further investigation is needed in larger populations to confirm the clinical benefits.     

Differences in genotype and allele frequency distributions of polymorphic drug metabolizing enzymes CYP2C19 and CYP2D6 in mainland Chinese Mongolian, Hui and Han populations

What is known and Objective: Cytochrome P450 2C19 (CYP2C19) and CYP2D6 are important xenobiotic metabolic enzymes and both show considerable genetic variability between Orientals and Caucasians. There are known marked heterogeneity in susceptibility to various cancers and hypertension among Chinese Mongolian, Hui and Han ethnic groups, but the molecular mechanisms are unknown. Our objective was to investigate the patterns of distribution of CYP2C19 and CYP2D6 polymorphisms among healthy Chinese subjects to determine whether any observed inter‐ethnic variability might be worth further investigation as possible contributors to the known differences in disease prevalence. Methods: Blood samples were collected from 454 unrelated Chinese healthy subjects (214 Han, 111 Hui, 129 Mongolian) for genotyping analysis. The single nucleotide polymorphisms (SNPs) CYP2C19*2 (681G>A in exon 5), CYP2C19*3 (636G>A in exon 4) and CYP2D6*10 (188C>T in exon 1) were determined by the polymerase chain reaction–restriction fragment length polymorphism (PCR‐RFLP) method. Results and Discussion: Significantly higher frequencies of the CYP2C19 poor metabolic genotypes were observed in Chinese Han (18·7%), Chinese Hui (25·0%) and Chinese Mongolian (10·9%) subjects than has been reported for Caucasians (1·7–3·0%, P < 0·01). The prevalent defective allele CYP2C19*2 occurred more frequently in both Chinese Hui (32·4%) and Han (29·7%) than in Chinese Mongolian (18·2%, P < 0·01) subjects. The CYP2C19*2 and CYP2C19*3 defective alleles were significantly more frequent in Chinese Han and Chinese Hui ethnic groups than have been reported for Caucasians (11·1–16·3% and 0–0·2%, P < 0·01). CYP2D6*1/*10 heterozygotes and CYP2D6*10/*10 homozygotes were observed more frequently in Chinese Han (43·1% and 27·2%), Hui (40·6% and 30·7%) and Mongolian subjects (31·3% and 9·6%, both P < 0·01) than have been reported for Caucasians (5·5% and 0·3%, P < 0·01). In Chinese Mongolians, the CYP2D6*10 allele occurred at a frequency (25·2%, P < 0·01) intermediate between those reported for Caucasians and the other two Chinese ethnic populations. What is new and Conclusions: This is first report of interethnic differences in frequencies of functional CYP2C19 and CYP2D6 genes among Chinese Mongolian, Hui and Han populations. These differences may be important in explaining reported inter‐ethnic differences in disease prevalence and response to drugs.     

Smoking behaviour modulates pharmacokinetics of orally administered clopidogrel

Background and objectives: Clopidogrel is an important antiplatelet drug that is effective in preventing thrombotic events, especially for patients undergoing percutaneous coronary intervention. The therapeutic usefulness of clopidogrel has been limited by documented inter‐individual heterogeneity in platelet inhibition, which may be attributable to known clopidogrel pharmacokinetic variability. The objective of this study was to assess the influence of smoking cigarettes and abnormal body weight on the pharmacokinetics of clopidogrel. Methods: Seventy‐six healthy adult male volunteers were selected randomly. Each subject received a single 75 mg oral dose of clopidogrel after overnight fast. Clopidogrel carboxylate plasma levels were measured and non‐compartmental analysis was used to determine peak plasma concentration (C_max), time to peak plasma concentration (T_max), elimination half‐life (t_1/2e), and area under the curve (AUC_0→∞). Results: One‐third of volunteers were smokers (n = 27) and one‐half had abnormal body weight (n = 39). Smokers had lower AUC_0→∞ (smokers: 6·24 ± 2·32 μg/h/mL vs. non‐smokers: 8·93 ± 3·80 μg/h/mL, P < 0·001) and shorter half‐life (smokers: 5·46 ± 2·99 vs. non‐smokers: 8·43 ± 4·26, P = 0·001). Smoking behaviour had no influence on C_max (P = 0·3) and T_max (P = 0·7). There was no statistically significant difference in C_max, AUC_0→∞, T_max and t_1/2e between volunteers with abnormal body weight and normal body weight. However the difference in body weight of the two groups was relatively narrow (mean ± SE; 26·93 ± 0·16 vs. 23·11 ± 0·27). In general, the pharmacokinetic parameters were characterized by considerable inter‐individual differences (C_max = 3·09 ± 0·99 μg/mL, CV = 32%), (T_max =0·76 ± 0·24 h, CV = 31·6%), (AUC_0→∞ = 7·98 ± 3·58 μg/h/mL, CV = 44·8%), and (t_1/2e = 7·38 ± 4·10 h, CV = 55·6%). Conclusion: Smoking is a significant factor affecting the pharmacokinetics of clopidogrel, following administration of a single 75 mg dose in healthy young volunteers. The study supports smoking‐cessation recommendations. Further studies are required to evaluate the influence of smoking and body weight on the pharmacokinetics of the active metabolite of clopidogrel and on the clinical effects of any differences observed.     

Personalized Tacrolimus Doses Determined by CYP3A5 Genotype for Induction and Maintenance Phases of Kidney Transplantation

Background

Cytochrome P450 (CYP) 3A4 and 3A5 are major isoforms involved in the metabolism of tacrolimus, with the CYP3A5 gene being more polymorphic. It is hypothesized that individual variation in the metabolism of tacrolimus drug may result from genetic polymorphism of CYP3A5. It has been reported that the clearance of tacrolimus in patients with the CYP3A5*1 allele was ~2.5-fold greater than that in those with the CYP3A5*3/*3 genotype. Recent data have also shown that polymorphism in exon 26 (C3435T) of the multidrug resistance gene (MDR1) was correlated with the expression level and function of P-glycoprotein in the lower duodenum, making the relationship between polymorphism of MDR1 and the effective dose of tacrolimus a source of controversy.

Objectives

This study investigated the influence of genetic polymorphisms of CYP3A5 and MDR1 on the dose requirements for the induction and maintenance phases of tacrolimus therapy in kidney transplant recipients.

Methods

Sixty-eight kidney transplant recipients were enrolled, and their clinical and laboratory data were retrospectively reviewed after 6 months of tacrolimus administration. Genotypes of CYP3A5*1 and CYP3A5*3 and exon 26 of MDR1 (C3435T) were determined by the single-nucleotide polymorphism genotyping method.

Results

The frequencies of CYP3A5*3/*3, CYP3A5*1/*3, and CYP3A5*1/*1 were 44.1%, 35.3%, and 20.6%, respectively. The mean dose of tacrolimus required for the induction phase was significantly greater in the CYP3A5*1/*1 group (0.142 [0.050] mg/kg/d) than that required in the CYP3A5*1/*3 group (0.097 [0.040] mg/kg/d; P = 0.072) and in the CYP3A5*3/*3 group (0.077 [0.020] mg/kg/d; P = 0.005). The maintenance dose of tacrolimus required in the CYP3A5*1/*1 group (0.12 [0.03] mg/kg/d) was 1.3-fold higher than that in the CYP3A5*1/*3 group (0.09 [0.03] mg/kg/d; P = 0.018) and 2.4-fold higher than in the CYP3A5*3/*3 group (0.05 [0.02] mg/kg/d; P < 0.0001). No statistically significant relationship was observed between the doses of tacrolimus required for the induction and maintenance phases and MDR1 polymorphism.

Conclusion

Determination of the CYP3A5 genotype would be helpful in the design of adequate immunosuppressive treatment and in lowering toxicity by predicting the doses of tacrolimus required for the induction and maintenance phases in individual kidney transplant recipients.     

Genetic polymorphisms of the CYP3A4, CYP3A5, and MDR-1 genes and pharmacokinetics of the calcineurin inhibitors cyclosporine and tacrolimus

BACKGROUND: The calcineurin inhibitors cyclosporine (INN, cyclosporin) and tacrolimus have a narrow therapeutic index and show considerable interindividual variability in their pharmacokinetics. The low oral bioavailability of calcineurin inhibitors is thought to result from the actions of the metabolizing enzymes cytochrome P450 (CYP) 3A4 and CYP3A5 and the multidrug efflux pump P-glycoprotein, encoded by MDR-1. OBJECTIVE: Our objective was to determine the role of genetic polymorphisms in CYP3A4, CYP3A5, and MDR-1 with respect to interindividual variability in cyclosporine and tacrolimus pharmacokinetics. METHODS: Kidney transplant recipients receiving cyclosporine (n = 110) or tacrolimus (n = 64) were genotyped for CYP3A4*1B and *3, CYP3A5*3 and *6, and MDR-1 C3435T. Dose-adjusted trough levels were determined and correlated with the corresponding genotype. RESULTS: Tacrolimus dose-adjusted trough levels were higher in CYP3A5*3/*3 patients (n = 45) than in *1/*3 plus *1/*1 patients (n = 17), as follows: median and range, 94 (34-398) ng/mL per mg/kg versus 61 (37-163) ng/mL per mg/kg (P <.0001, Mann-Whitney test). CYP3A4*1B allele carriers (n = 10) had lower tacrolimus dose-adjusted trough levels compared with those in patients with the wild-type (*1/*1) genotype (n = 54): median and range, 57 (40-163) ng/mL per mg/kg versus 89 (34-398) ng/mL per mg/kg) (P =.003, Mann-Whitney test). No evidence was found supporting a role for the MDR-1 C3435T polymorphism in tacrolimus dose requirement. None of the polymorphisms studied correlated with cyclosporine dose-adjusted predose concentrations. CONCLUSION: As a group, patients with the CYP3A5*3/*3 genotype require less tacrolimus to reach target predose concentrations compared with CYP3A5*1 allele carriers, whereas CYP3A4*1B carriers require more tacrolimus to reach target trough concentrations compared with CYP3A4*1 homozygotes.     

Effect of polymerized-type I collagen in knee osteoarthritis. II. In vivo study

Background Polymerized‐Type I Collagen (Polymerized‐Collagen) is an anti‐inflammatory and a tissue regenerator biodrug. The aim of the study was to evaluate the efficacy and safety of intra‐articular injections of Polymerized‐Collagen in patients with knee osteoarthritis (OA). Methods and design Patients (n = 53) were treated with 12 intra‐articular injections of 2 mL of Polymerized‐Collagen (n = 27) or 2 mL of placebo (n = 26) during 6 months. Follow up period was 6 months. The primary endpoints included Western Ontario and McMaster University Osteoarthritis Index, Lequesne index, and pain intensity on a visual analogue scale (VAS). Secondary outcomes were patient global score, investigator global score and drug evaluation. Clinical improvement was determined if the decrease in pain exceeds 20 mm on a VAS and patients achieved at least 20% of improvement from baseline. Urinary levels of C‐terminal crosslinking telopeptide of collagen type II (CTXII) and serum high‐sensitivity C‐reactive protein (hsCRP) were determined by enzyme immunoassays. Statistical analysis was performed by intention to treat. Results Polymerized‐Collagen was safe and well tolerated. Patients had a statistically significant improvement (P < 0·05) from baseline vs. Polymerized‐Collagen and vs. placebo at 6 months in: Lequesne Index (13·1 ± 0·5 vs. 7·1 ± 0·7 vs. 9·6 ± 0·8; P = 0·027), WOMAC (9·0 ± 0·5 vs. 4·0 ± 0·6 vs. 5·80 ± 0·8; P = 0·032), patient VAS (60·0 ± 2·6 vs. 20·6 ± 2·4 vs. 36·1 ± 4·5; P = 0·003), physician VAS (49·8 ± 1·9 vs. 16·8 ± 2·9 vs. 29·8 ± 2·9; P = 0·002), patient global score (1·08 ± 0·1 vs. 2·7 ± 0·1 vs. 1·9 ± 0·2; P = 0·028) and analgesic usage (30·1 ± 9·4 vs. 11·0 ± 3·4 vs. 17·9 ± 4·9; P = 0·001). This improvement was persistent during the follow up. A threefold increase in CTXII was determined in placebo group. No differences were found on hs CRP and incidence of adverse events between groups. Conclusion Polymerized‐Collagen is safe and effective in the treatment of knee OA.     

Determination of glycyrrhetic acid in human plasma by HPLC-MS method and investigation of its pharmacokinetics

Objective: To develop a high performance liquid chromatography mass spectrometry (HPLC‐MS) method for the determination of the glycyrrhetic acid (GA) in human plasma and for the investigation of its pharmacokinetics after the oral administration of 150 mg diammonium glycyrrhizinate test and reference capsule formulations. Methods: The GA in plasma was extracted with ethyl acetate, separated on a C₁₈ column with a mobile phase of methanol (5 mmol/L ammonium acetate)–water (85 : 15, V/V) and analysed using a MS detector. Ursolic acid (UA) was used as internal standard. The target ions were m/z 469·5 for GA and m/z 455·6 for UA, the fragment voltages were 200 V and 100 V for GA and UA respectively. Results: The calibration curve was linear over the range of 0·5–200 ng/mL (r = 0·9974). The limit of quantification for GA in plasma was 0·5 ng/mL, the recovery was 76·0–80·0%, and the inter‐ and intra‐day relative standard deviations (RSD) were <12%. The pharmacokinetic parameters of GA after a single dose of 150 mg diammonium glycyrrhizinate test and reference were as follows: the half life (t_1/2) 9·65 ± 3·54 h and 9·46 ± 2·85 h, the time to peak concentration (T_max) 10·95 ± 1·32 h and 11·00 ± 1·30 h, the peak concentration (C_max) 95·57 ± 43·06 ng/mL and 103·89 ± 49·24 ng/mL; the area under time‐concentration curve (AUC_0–48 and AUC_0–∞) 1281·84 ± 527·11 ng·h/mL and 1367·74 ± 563·27 ng·h/mL, 1314·32 ± 566·40 ng·h/mL and 1396·97 ± 630·06 ng·h/mL. The relative bioavailability of diammonium glycyrrhizinate capsule was 98·88 ± 12·98%. Conclusion: The assay was sensitive, accurate and convenient, and can be used for the determination of GA in human plasma. Comparison of the bioavailability and pharmacokinetic profile of GA indicated that the test and reference capsules were bioequivalent.     

CYP4F2 gene polymorphism as a contributor to warfarin maintenance dose in Japanese subjects

What is known and Objective: Polymorphisms in the gene encoding CYP4F2 may partly explain the variability in warfarin maintenance dose by altering the metabolism of vitamin K. To determine the genetic factors that cause large inter‐patient variability in warfarin efficacy, we investigated the relationship between serum warfarin concentration and CYP4F2 V433M (1347C>T, rs2108622) polymorphism in Japanese subjects. Methods: Gene variations in VKORC1, CYP2C9 and CYP4F2 were analysed in 126 Japanese patients treated with warfarin. The daily dosage of warfarin, concentration of S‐ and R‐warfarin in plasma, and prothrombin time international normalized ratio (PT‐INR) was used as the pharmacokinetic and pharmacodynamic indices. Results and Discussion: The maintenance dose of warfarin was larger in the CYP4F2 1347 CT genotype group (3·59 ± 1·80 mg/day, P = 0·027) than in the CYP4F2 CC genotype group (2·88 ± 1·00 mg/day). CYP4F2 1347C>T polymorphism significantly affected serum R‐warfarin concentration when the VKORC1‐1639 genotypes are AG and GG. What is new and Conclusion: Although a significant inter‐patient difference in warfarin maintenance dose was observed between the CYP4F2 CC and CT genotypes, serum S‐warfarin concentration was not significantly different between them. An effect of CYP4F2 V433M polymorphism on warfarin maintenance dose was observed but was relatively small when compared to the effects of CYP2C9 and VKOR polymorphism.     

OATP1B1 388A>G polymorphism and pharmacokinetics of pitavastatin in Chinese healthy volunteers

Purpose: To investigate the contribution of the most frequent single nucleotide polymorphism (SNPs) of the organic anion transporting polypeptide 1B1 (OATP1B1) 388A>G to the pharmacokinetics of pitavastatin in Chinese healthy volunteers. Methods: Eighteen healthy volunteers participated in this study. Group 1 consisted of nine subjects who were of 388AA wild‐type OATP1B1 genotype. Group 2 consisted of seven subjects with the 388GA genotype and two 388GG homozygotes. Two milligram of pitavastatin was administered orally to the volunteers. The plasma concentration of pitavastatin was measured for up to 48 h by liquid chromatography–mass spectrometry (LC–MS). Results: The pharmacokinetic parameters of pitavastatin were significantly different between the two genotyped groups. The concentration (C_max) value was higher in the 388GA + 388GG group than that in the 388AA group (39·22 ± 8·45 vs. 22·90 ± 4·03 ng/mL, P = 0·006). The area under the curve to the last measurable concentration (AUC_0–48) and area under the curve extrapolated to infinity (AUC_0–∞) of pitavastatin were lower in the 388AA group than in the 388GA + 388GG group (100·42 ± 21·19 vs. 182·19 ± 86·46 ng h/mL, P = 0·024; 108·12 ± 24·94 vs. 199·64 ± 98·70ng h/mL, P = 0·026) respectively. The oral clearance (Cl/F) was lower in the 388GA + 388GG group than that in the 388AA group (12·46 ± 4·79 vs. 19·21 ± 3·74/h, P = 0·012). The elimination of half‐life (t_1/2) and peak concentration times (T_max) values showed no difference between these groups. Conclusions: The OATP 388A>G polymorphism causes significant alterations in the pharmacokinetics of pitavastatin in healthy Chinese volunteers and this may well be clinically significant.     

Cytochrome P450 CYP2C19 genotypes in Nigerian sickle‐cell disease patients and normal controls

Background and objective: Subjects with different CYP2C19 genotypes may metabolize proguanil, a pro‐drug used for malaria prophylaxis differently and the frequency of the different alleles may be different in patients with sickle‐cell disease (SCD) and normal controls. The objective of this study was to evaluate CYP2C19 *1, *2 and *3 allele and genotype frequencies in Nigerian normal controls and SCD patients, and to further compare variant CYP2C19 frequencies in Nigerians with other African populations. Methods: Genotyping was carried out with PCR and restriction fragment length polymorphism analysis. Results and discussion: CYP2C19 *1 (84·3 vs. 84·9%) or *2 allele frequency (15·7 vs. 15·1%) was not significantly different between patients with SCD and normal subjects. No *3 allele was detected in the cohort. The SCD group exhibited a statistically significantly lower frequency of *1/*1 genotype (69·6%) compared with normal controls (74·4%). Frequency of *2/*2 was significantly lower in SCD (0·9%) compared with normal controls (4·7%). Frequencies of *1/*2 (29·6 vs. 20·9%) were no different in SCD and normal controls. Conclusion: Prevalence of CYP2C19 polymorphisms was defined for the first time in Nigerian normal and SCD populations. Nigerian SCD patients exhibited significantly lower CYP2C19 *1/*1 and *2/*2 frequencies than normal controls. No differences were detected in CYP2C19 allele or genotype frequencies in normal subjects between this study and previous reports in other African populations.     

Distribution of CYP2C19*17 allele and genotypes in an Indian population

What is known and Objective: CYP2C19*17 allele increases the metabolic activity of CYP2C19 resulting in decreased therapeutic levels of CYP2C19 substrates. There exist inter‐ethnic differences in the distribution of this allele. The present study was aimed at establishing the allele and genotype frequencies of CYP2C19*17 in a South Indian Tamilian population. Furthermore, we describe the haplotype structure of the three common variant alleles of CYP2C19 in the Tamilian population. Methods: Two hundred and six subjects of South Indian Tamilian origin were genotyped for CYP2C19*17 allele by nested polymerase chain reaction and restriction fragment length polymorphism. A subset of 87 subjects were also genotyped for CYP2C19*2 and CYP2C19*3 alleles. After ascertaining linkage disequilibrium (LD), haplotypes were constructed. Allele and genotype frequencies, LD pattern and haplotype frequency were compared with those of the HapMap populations. Results and Discussion: The CYP2C19*17 allele frequency in the Tamilian population (n = 206) was found to be 19·2% (95% CI: 15·4 – 20·3). The CYP2C19*2 allele frequency (n = 87) was found to be 40·2% (95% CI: 32·9 – 47·5), whereas the CYP2C19*3 allele was not detected in the study subjects (n = 97). The high frequency of the CYP2C19*17 allele in the study population has resulted in a revision of frequencies for CYP2C19*1/*2 (31·0%) and CYP2C19*1/*1 (16·1%) genotypes in the Tamilian population. We also observed significant differences in haplotype structure and frequencies of these variant alleles in the HapMap population compared to Tamilian population. What is new and conclusion: CYP2C19*17 allele is present at high frequency in the Tamilian population. This study also demonstrates the need for reassessment of wild‐type allele frequencies in view of CYP2C19*17 allele. The estimated high frequency of CYP2C19*17 allele will aid in genotype–phenotype association studies in the Tamilian population. Further genotype–phenotype association studies are required to evaluate the clinical utility of this allele in South Indians.     

Effect of cytochrome P450 3A4 inhibitor ketoconazole on risperidone pharmacokinetics in healthy volunteers

What is known and objective: Risperidone is an atypical antipsychotic agent used for the treatment of schizophrenia. It is mainly metabolized by human cytochrome P450 CYP2D6 and partly by CYP3A4 to 9‐hydroxyrisperidone. Ketoconazole is used as a CYP3A4 inhibitor probe for studying drug–drug interactions. We aim to investigate the effect of ketoconazole on the pharmacokinetics of risperidone in healthy male volunteers. Methods: An open‐label, randomized, two‐phase crossover design with a 2‐week washout period was performed in 10 healthy male volunteers. The volunteers received a single oral dose of 2 mg of risperidone alone or in combination with 200 mg of ketoconazole, once daily for 3 days. Serial blood samples were collected at specific periods after ingestion of risperidone for a period of 96 h. Plasma concentrations of risperidone and 9‐hydroxyrisperidone were determined using a validated HPLC–tandem mass spectrometry method. Results and discussion: After pretreatment with ketoconazole, the clearance of risperidone decreased significantly by 34·81 ± 15·10% and the T_1/2 of risperidone increased significantly by 28·03 ± 40·60%. The AUC_0–96 and AUC_0–∞ of risperidone increased significantly by 66·61 ± 43·03% and 66·54 ± 39·76%, respectively. The Vd/f of risperidone increased significantly by 39·79 ± 53·59%. However, the C_max and T_max of risperidone were not significantly changed, indicating that ketoconazole had minimal effect on the absorption of risperidone. The C_max, T_max and T_1/2 of 9‐hydroxyrisperidone did not decrease significantly. However, the Cl/f of 9‐hydroxyrisperidone increased significantly by 135·07 ± 124·68%, and the Vd/f of 9‐hydroxyrisperidone decreased significantly by 29·47 ± 54·64%. These changes led to a corresponding significant decrease in the AUC_0–96 and AUC_0–∞ of 9‐hydroxyrisperidone by 47·76 ± 22·39% and 48·49 ± 20·03%, respectively. Ketoconazole significantly inhibited the metabolism of risperidone through the inhibition of hepatic CYP3A4. Our results suggest that besides CYP2D6, CYP3A4 contributes significantly to the metabolism of risperidone. What is new and Conclusion: The pharmacokinetics of risperidone was affected by the concomitant administration of ketoconazole. If a CYP3A4 inhibitor is used concomitantly with risperidone, it is necessary for the clinicians to monitor their patients for signs of adverse drug reactions.     

Interactions between CYP7A1 A-204C and ABCG8 C1199A polymorphisms on lipid lowering with atorvastatin

What is known and Objective: Cholesterol excretion by ATP binding cassette transporters G5 and G8 (ABCG5/G8) and bile acid biosynthesis by 7a‐hydroxylase (CYP7A1) are major pathways for the removal of cholesterol into bile. This suggests that variations in the CYP7A1 and ABCG8 genes may influence the statin response. We aimed to investigate the effect of CYP7A1 A‐204C and ABCG8 C1199A polymorphisms and their interactions on the lipid‐lowering response to atorvastatin in a Chinese population. Methods: Genotypes were determined by using polymerase chain reaction‐restrict fragment length polymorphism (PCR‐RFLP) in 185 hyperlipidaemic patients treated with atorvastatin, 20 mg once daily for 4 weeks. Serum levels of triglycerides (TGs), total cholesterol (TC), low‐density lipoprotein cholesterol (LDL‐C), and high‐density lipoprotein cholesterol (HDL‐C) were determined before and after treatment. Results and Discussion: For 181 patients (89 males), variant allele frequencies of CYP7A1 ‐204C and ABCG8 1199A were 0·347 and 0·128, respectively. Among all patients, homozygotes for the ‐204A allele showed a slightly significant mean percentage reduction from baseline in TG level after treatment than heterozygotes and homozygotes for the ‐204C allele (?25·49 ± 8·12%vs. ?22·80 ± 8·72%, P = 0·054, and ?25·49 ± 8·12%vs.?22·51 ± 8·82%, P = 0·048, respectively). For patients with the ABCG8 C1199A variant allele, the difference in percentage reduction from baseline in TG level was increased between the CYP7A1 A‐204C wild‐type allele homozygotes and variant allele homozygotes after atorvastatin treatment (?28·35%vs.?19·28%, P = 0·001), and increased differences were found between the CYP7A1 A‐204C wild‐allele homozygotes and variant allele homozygotes (?18·95%vs.?15·61%, P = 0·009) and between the CYP7A1 A‐204C variant allele heterozygotes and homozygotes (?18·69%vs.?15·61%, P = 0·012, respectively). What is new and Conclusion: The CYP7A1 ‐204A and ABCG8 1199A alleles appear to interact to affect lipid‐lowering response to atorvastatin. However, given the relatively small number of subjects with the influential variant allele combinations, and the heterogeneity in response, even in the selected sub‐populations, testing would be of little clinical utility in the Chinese population sampled.