Effect of CYP2C19 polymorphism on nelfinavir to M8 biotransformation in HIV patients

Aims

To evaluate the effect of CYP2C19 polymorphism on nelfinavir and M8 pharmacokinetic variability in human immunodeficiency virus-infected patients and to study the link between pharmacokinetic exposure and short-term efficacy and toxicity.

Methods

Nelfinavir (n = 120) and M8 (n = 119) concentrations were measured in 34 protease inhibitor-naïve patients. Two weeks after initiating the treatment, blood samples were taken before, 1, 3 and 6 h after drug administration. Genotyping for CYP3A4, 3A5, 2C19 and MDR1 was performed. A population pharmacokinetic model was developed to describe nelfinavir-M8 concentration time-courses and to estimate interpatient variability. The influence of individual characteristics and genotypes were tested using a likelihood ratio test. Estimated mean (C_mean), maximal (C_max) and trough (C_trough) nelfinavir and M8 concentrations were correlated to short-term virological efficacy and tolerance using Spearman nonparametric correlation tests.

Results

A one-compartment model with first-order absorption, elimination and metabolism to M8 best described nelfinavir data. M8 was modelled by an additional compartment. Mean pharmacokinetic estimates and the corresponding intersubject variabilities were: absorption rate 0.17 h⁻¹ (99%), absorption lag time 0.82 h, apparent nelfinavir total clearance 52 l h⁻¹ (49%), apparent nelfinavir volume of distribution 191 l, M8 elimination rate constant 1.76 h⁻¹ and nelfinavir to M8 0.39 h⁻¹ (59%) in *1/*1 patients and 0.20 h⁻¹ in *1/*2 or *2/*2 patients for CYP2C19*2. Nelfinavir C_mean was positively correlated to glycaemia and triglyceride increases (P = 0.02 and P = 0.04, respectively).

Conclusions

The rate of metabolism of nelfinavir to M8 was reduced by 50% in patients with *1/*2 or *2/*2 genotype for CYP2C19 compared with those with *1/*1 genotype.

What is already known about this subject

• Nelfinavir is an HIV protease inhibitor, substrate of the transporter P-glycoprotein and metabolized via CYP2C19, CYP3A4 and CYP3A5 enzymes.
• Pharmacokinetic studies have shown wide interindividual variability of nelfinavir concentrations, some of this variability perhaps caused by variant drug metabolism or transporter genes.
• For CYP3A4*1B and CYP3A5*3 polymorphism, results from three studies are in agreement, showing no difference in nelfinavir concentrations between patients with these different genotypes.
• However, for MDR1 and CYP2C19 polymorphism, there have been contradictory studies, showing either no impact on nelfinavir concentration or modified concentrations which could influence virological response.

What this study adds

• Patients with an *1/*2 or *2/*2 genotype for CYP2C19 had a nelfinavir to M8 biotransformation divided by 2 compared with *1/*1 patients.
• No evidence of any influence of MDR1 polymorphism on nelfinavir absorption could be detected.

     

Pharmacogenetics of plasma efavirenz exposure in HIV-infected adults and children in South Africa

AimsGenetic factors, notably CYP2B6 516G→T [rs3745274] and 983T→C [rs28399499], explain much of the interindividual variability in efavirenz pharmacokinetics, but data from Africa are limited. We characterized relationships between genetic polymorphisms and plasma efavirenz concentrations in HIV-infected Black South African adults and children.MethodsSteady-state mid-dosing interval efavirenz concentrations were measured. We genotyped 241 polymorphisms in genes potentially relevant to efavirenz metabolism and transport, including ABCB1, CYP2A6, CYP2B6, CYP3A4, CYP3A5, NR1I2 and NR1I3.ResultsAmong 113 participants (59 adults and 54 children), minor allele frequencies for CYP2B6 516G→T, 983T→C, and 15582C→T [rs4803419] were 0.36, 0.07, and 0.09, respectively. Based on composite CYP2B6 15582/516/983 genotype, there were 33 extensive metabolizer, 62 intermediate metabolizer and 18 slow metabolizer genotypes. Median (IQR) mid-dose efavirenz concentrations were 1.44 (1.21–1.93) µg ml^–1, 2.08 (1.68–2.94) µg ml^–1 and 7.26 (4.82–8.34) µg ml^–1 for extensive, intermediate and slow metabolizers, respectively. In univariate analyses, a model that included composite genotype best predicted efavirenz concentrations (β = 0.28, 95% CI 0.21, 0.35, P = 2.4 × 10^–11). Among individual CYP2B6 polymorphisms, 516G→T best predicted efavirenz concentrations (β = 0.22, 95% CI 0.13, 0.30, P = 1.27 × 10⁻⁶). There was also associations with 983T→C (β = 0.27, 95% CI 0.10, 0.44, P = 0.002) and 15582C→T (β = 0.11, 95% CI 0.01, 0.22, P = 0.04). Associations were consistent in adults and children. No other polymorphisms were independently associated with efavirenz concentrations.ConclusionsComposite CYP2B6 genotype based on CYP2B6 516G→T, 983T→C, and 15582C→T best described efavirenz exposure in HIV-infected Black South African adults and children.     

CYP2C19 genotypes and omeprazole metabolism after single and repeated dosing when combined with clarithromycin

Objectives: Omeprazole is metabolized mainly by CYP2C19 which has two major mutations (CYP2C19*2 in exon5 and CYP2C19*3 in exon4) associated with the poor metabolizer (PM) phenotype. The aim of this study was to examine the relationship between genetic polymorphism of CYP2C19 and metabolism of omeprazole administrated as a single dose or as repeated-doses, which were in both cases co-administered with clarithromycin. Methods: Twelve healthy Japanese subjects were typed for CYP2C19 polymorphism. In the single-dose study, plasma levels of omeprazole and its metabolites were measured for 24 h after administration of 20 mg omeprazole and 400 mg clarithromycin to six healthy Japanese subjects. In the repeated-dose study, plasma levels of omeprazole and its metabolites were measured after repeated oral administration of 20 mg omeprazole and 400 mg clarithromycin twice daily for 6 days and then after 20 mg omeprazole and 400 mg clarithromycin once on the 7th day to the other 6 healthy Japanese subjects. Results: In the single-dose study, the areas under the plasma concentration-versus-time curve (AUCs) of omeprazole of homozygotes for the wild-type allele (*1/*1 n = 2), heterozygotes (n = 3) for the CYP2C19*2 (*1/*2) or for the CYP2C19*3 (*1/*3) and heterozygote (n = 1) for the two defects (*2/*3) were on average 450, 1007 and 6710 ng · h⁻¹ · ml⁻¹, respectively. The ratios of AUCs of omeprazole/5-hydroxyomeprazole for *1/*1, *1/*2 or *1/*3 and *2/*3 were 1, 2 and 30, respectively. In the repeated-dose study, the AUCs of omeprazole for *1/*1, *1/*2 or *1/*3 and *2/*3 were 4041 (n = 2), 3149 (n = 3) and 6684 (n = 1) ng · h⁻¹ · ml⁻¹, respectively. The ratios of AUCs of omeprazole/5-hydroxyomeprazole for *1/*1, *1/*2 or *1/*3 and *2/*3 were 7, 11 and 30, respectively. In the repeated-dose study, the AUC of omeprazole of *1/*1 genotypes was nine-fold higher, that of *1/*2 and *1/*3 genotypes was three-fold higher, and the C_max value of omeprazole was three-fold higher compared with subjects with the same genotype in the single-dose study. However, there were few differences in the AUC and C_max of omeprazole between the *2/*3 genotype in the single-dose study and the homozygote for the CYP2C19*2 (*2/*2) in the repeated-dose study. Conclusion: Subjects with *1/*1, *1/*2 and *1/*3 genotypes in the repeated-dose study had lower CYP2C19 activity than subjects of the same genotype in the single-dose study. The difference in omeprazole metabolism between subjects with different genotypes observed on day 1 seemed to disappear after 7 days of repeated-dose administration. Received: 5 June 1998 / Accepted in revised form: 27 October 1998     

Pharmacokinetic and pharmacodynamic analysis of enteric-coated mycophenolate sodium: limited sampling strategies and clinical outcome in renal transplant patients

AIMS

Pharmacokinetic (PK) and pharmacodynamic (PD) monitoring strategies and clinical outcome were evaluated in enteric-coated mycophenolate sodium (EC-MPS)-treated renal allograft recipients.

METHODS

PK [mycophenolic acid (MPA)] and PD [inosine monophosphate dehydrogenase (IMPDH) activity] data were analysed in 66 EC-MPS and ciclosporin A (CsA)-treated renal allograft recipients. Adverse events were considered in a follow-up period of 12 weeks.

RESULTS

Analyses confirmed a limited sampling strategy (LSS) consisting of PK and PD data at predose, 1, 2, 3 and 4 h after oral intake as an appropriate sampling method (MPA r²= 0.812; IMPDH r²= 0.833). MPA AUC_0–12 of patients with early biopsy-proven acute rejection was significantly lower compared with patients without a rejection (median MPA AUC_0–12 28 µg*h ml⁻¹ (7–45) vs. 40 µg*h ml⁻¹ (16–130), P < 0.01), MPA AUC_0–12 of patients with recurrent infections was significantly higher compared with patients without infections (median MPA AUC_0–12 65 µg*h ml⁻¹ (range 37–130) vs. 37 µg*h ml⁻¹ (range 7–120), P < 0.005). Low 12-h IMPDH enzyme activity curve (AEC_0–12) was associated with an increased frequency of gastrointestinal side-effects (median IMPDH AEC_0–12 43 nmol*h mg⁻¹ protein h⁻¹[range 12–67) vs. 75 nmol*h mg⁻¹ protein h⁻¹ (range 15–371), P < 0.01].

CONCLUSIONS

Despite highly variable absorption data, an appropriate LSS might be estimated by MPA AUC_0–4 and IMPDH AEC_0–4 in renal transplant patients treated with EC-MPS and CsA. Regarding adverse events, the suggested MPA-target AUC_0–12 from 30 to 60 µg*h ml⁻¹ seems to be appropriate in renal allograft recipients.     

CYP2C19 polymorphism affects single-dose pharmacokinetics of oral pantoprazole in healthy volunteers

Objectives

Pantoprazole is metabolized by cytochrome P450 2?C19, which shows genetic polymorphism. The effect of CYP2C19 polymorphism on single-dose pharmacokinetics of oral pantoprazole in healthy volunteers was evaluated.

Methods

Pantoprazole pharmacokinetics was determined in 32 healthy volunteers after a 40-mg single oral dose of the drug.

Results

Carriers of CYP2C19*2/*2 (n?=?2) were characterized by higher, starting from 3.5?h post dose, plasma concentrations of pantoprazole in comparison to wild-type (CYP2C19*1/*1, n?=?6) volunteers. In subjects with CYP2C19*17/*17 genotype (n?=?6) significantly lower plasma concentrations of the drug vs CYP2C19*1/*1 carriers, were observed from 3.0?h after oral pantoprazole administration. Carriers of CYP2C19*1/*17 (n?=?6) and CYP2C19*2/*17 (n?=?6) displayed concentration–time profiles comparable to wild-type subjects. CYP2C19*2/*2 volunteers showed a decrease in terminal elimination rate constant (λ_z) by 83.3%, prolongation of terminal half-life (t_?) by 572%, a rise in area under the concentration–time curve (AUC) and mean residence time (MRT) by 506% and 259% respectively. Heterozygotes, i.e.. CYP2C19*1/*2 vs CYP2C19*1/*1 were characterized by higher AUC (4.38?±?1.00?mg?h/L vs 3.00?±?1.02 mg?h/L, p?max (2.13?±?0.42?mg/L vs 1.61?±?0.35?mg/L, p?p?CYP2C19*17/*17 vs CYP2C19*1/*1 genotypes was observed. Population modeling confirmed the influence of *1/*2, *2/*2, and *17/*17 genotypes on the pharmacokinetics of pantoprazole. The lowest population oral clearance was assessed in the carriers of genotype *2/*2 (3.68?L/h) and the highest value in subjects with genotype *17/*17 (31.13?L/h).

Conclusion

These data suggest that CYP2C19 polymorphism is an important determinant of pantoprazole pharmacokinetics.     

Impact of visceral leishmaniasis and curative chemotherapy on cytochrome P450 activity in Brazilian patients

Aims

The aim of the present study was to investigate the impact of human visceral leishmaniasis (VL) and curative chemotherapy on the activity of cytochrome P450 (CYP) 3A, CYP2C9 and CYP2C19 in patients from an endemic region in Brazil.

Methods

Adult patients with parasitologically confirmed VL were given a CYP phenotyping cocktail, comprising midazolam, omeprazole and losartan, immediately before (Study phase 1), 2–3 days (phase 2) and 3–6 months (phase 3) after curative VL chemotherapy. CYP activity was assessed by the apparent clearance of midazolam (CYP3A), omeprazole/5-hydroxyomeprazol ratio in plasma (CYP2C19) and losartan/E3174 ratio in urine (CYP2C9).

Results

Mean values (95% confidence interval) in phases 1, 2 and 3 were, respectively: log apparent midazolam clearance, 1.21 (1.10–1.31), 1.45 (1.32–1.57) and 1.35 (1.26–1.44) ml min^–1 kg^–1; omeprazole/5-hydroxyomeprazole ratio, 0.78 (0.61–0.94), 0.45 (0.27–0.63) and 0.37 (0.20-0.55); losartan/E3174 ratio, 0.66 (0.39–0.92), 0.35 (0.20–0.50) and 0.35 (0.16–0.53). Analysis of variance revealed significant differences in CYP3A (P = 0.018) and CYP2C19 (P = 0.008), but not CYP2C9 (P = 0.11) phenotypic activity, across the three study phases.

Conclusion

The phenotypic activities of CYP3A4 and CYP2C19 were significantly reduced during acute VL compared with post-chemotherapy. We propose that increased plasma concentrations of proinflammatory cytokines during active disease account for the suppression of CYP activity. The failure to detect significant changes in CYP2C9 activity in the overall cohort may reflect differential effects of the inflammatory process on the expression of CYP isoforms, although the possibility of insufficient statistical power cannot be dismissed.     

Hydroxylation index of omeprazole in relation to CYP2C19 polymorphism and sex in a healthy Iranian population

Background

Polymorphism of CYP2C19 gene is one of the important factors in pharmacokinetics of CYP2C19 substrates. Omeprazole is a proton pump inhibitor which is mainly metabolized by cytochrome P450 2C19 (CYP2C19). The aim of present study was to assess omeprazole hydroxylation index as a measure of CYP2C19 activity considering new variant allele (CYP2C19*17) in Iranian population and also to see if this activity is sex dependent.

Methods

One hundred and eighty healthy unrelated Iranian individuals attended in this study. Blood samples for genotyping and phenotyping were collected 3 hours after administration of 20 mg omeprazole orally. Genotyping of 2C19 variant alleles *2, *3 and *17 was performed by using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and semi-nested PCR methods. Plasma concentrations of omeprazole and hydroxyomeprazole were determined by high performance liquid chromatography (HPLC) technique and hydxroxylation index (HI) (omeprazole/ hydroxyomeprazole) was calculated.

Results

The CYP2C19*17 was the most common variant allele in the studied population (21.6%). Genotype frequencies of CYP2C19*17*17, *1*17, and *2*17 were 5.5%, 28.8% and 3.3% respectively. The lowest and the highest median omeprazole HI was observed in *17*17 and *2*2 genotypes respectively (0.36 vs. 13.09). The median HI of omeprazole in subjects homozygous for CYP2C19*1 was 2.16-fold higher than individuals homozygous for CYP2C19*17 (P < 0.001) and the median HI of CYP2C19*1*17 genotype was 1.98-fold higher than CYP2C19 *17*17 subjects (P < 0.001). However, subjects with CYP2C19*2*17 (median HI: 1.74) and CYP2C19*1*2 (median HI: 1.98) genotypes and also CYP2C19*1*17 (median HI: 0.71) and CYP2C19*1*1 (mean HI: 0.78) did not show any significantly different enzyme activity. In addition, no statistically significant difference was found between women and men in distribution of CYP2C19 genotypes. Furthermore, the hydroxylation index of Omeprazole was not different between women and men in the studied population.

Conclusion

Our data point out the importance of CYP2C19*2 and CYP2C19*17 variant alleles in metabolism of omeprazole and therefore CYP2C19 activity. Regarding the high frequency of CYP2C19*17 in Iranian population, the importance of this new variant allele in metabolism of CYP2C19 substrates shall be considered.     

Progressive decline in tacrolimus clearance after renal transplantation is partially explained by decreasing CYP3A4 activity and increasing haematocrit

Aims

The long-term disposition of tacrolimus following kidney transplantation is characterized by a gradual decrease in dose requirements and increase in dose-corrected exposure. This phenomenon has been attributed to a progressive decline in cytochrome P450 3A4 (CYP3A4) activity, although this has never been demonstrated in vivo.

Methods

Sixty-five tacrolimus- and 10 cyclosporine-treated renal transplant recipients underwent pharmacokinetic testing at day 7 and months 1, 3, 6 and 12 after transplantation, including 8-h area under the concentration-time curve (AUC) for tacrolimus or cyclosporine and assessment of CYP3A4 activity using oral and intravenous midazolam (MDZ) drug probes.

Results

Tacrolimus clearance decreased gradually throughout the entire first year but only in CYP3A5*3/*3 homozygous recipients (25.6 ± 11.1 l h^–1 at day 7; 17 ± 9.1 l h^–1 at month 12; P < 0.001). In mixed model analysis, decreasing CYP3A4 activity, measured by apparent oral MDZ clearance (924 ± 443 ml min^–1 at day 7 vs. 730 ± 344 ml min^–1 at month 1; P < 0.001), explained 55.4% of the decline in tacrolimus clearance in the first month. CYP3A4 activity decreased by 18.9 ml min^–1 for every milligram of methylprednisolone dose tapering within the first month; beyond this point it remained stable. A gradual rise in haematocrit throughout the entire first year explained 31.7% of the decrease in tacrolimus clearance in the first month and 23.6% of the decrease between months 1 and 12. Cyclosporine clearance did not change over time.

Conclusions

The maturation of tacrolimus disposition in the first year after renal transplantation observed in CYP3A5*3/*3 homozygous patients can partly be explained by a (steroid tapering-related) decline in CYP3A4 activity and a progressive increase in haematocrit.     

CYP2B6*6 allele and age substantially reduce steady-state ketamine clearance in chronic pain patients: impact on adverse effects

Aims

Ketamine analgesia is limited by low intrinsic efficacy compounded by large interindividual variability in drug responses, possibly due to the heterogeneity in drug concentration. The CYP2B6*6 allele is associated with substantially reduced ketamine metabolism in vitro and, therefore, may affect ketamine clearance. Our aims were to examine the impact of the CYP2B6*6 allele on ketamine plasma clearance and on adverse effects in chronic pain patients.

Methods

CYP2B6 genotypes were identified in 49 chronic pain patients who received 24 h continuous subcutaneous infusions of ketamine. Steady-state plasma concentrations of ketamine (C_ss,k) and norketamine (C_ss,nk) were determined using HPLC.

Results

The median plasma clearance of ketamine after 100 mg 24 h^–1 dose was significantly lower in patients with the CYP2B6*6/*6 (21.6 l h^–1) and CYP2B6*1/*6 (40.6 l h^–1) genotypes compared with patients with the CYP2B6*1/*1 genotype (68.1 l h^–1, P < 0.001). The ketamine : norketamine plasma metabolic ratio was significantly higher in patients with the CYP2B6*6/*6 genotype than in those with the CYP2B6*1/*6 and the CYP2B6*1/*1 genotypes (P < 0.001). Patients who experienced adverse effects had lower plasma clearance (45.6 l h^-1) than those who did not (52.6 l h^-1, P = 0.04). The CYP2B6*6 genotype and age, and their combined impact explained 40%, 30% and 60% of the variation in C_ss,k, respectively. Similar results were observed after higher doses.

Conclusions

The CYP2B6*6 allele is associated with a substantial decrease in steady-state ketamine plasma clearance in chronic pain patients. The decreased clearance and resultant higher plasma concentrations may be associated with a higher incidence of ketamine adverse effects.     

Cytochrome P 450 2C9 phenotyping using low-dose tolbutamide

Objectives The hypoglycaemic drug tolbutamide is used for assessment of CYP2C9 activity in vivo. However, therapeutically active doses of 500 mg bear the risk of hypoglycaemia, and a tolbutamide-derived parameter based on a single plasma or urine concentration reflecting CYP2C9 activity accurately is lacking.Methods We examined tolbutamide and its metabolites 4-hydroxy-tolbutamide and carboxytolbutamide in plasma and urine of 26 healthy, male volunteers up to 24 h after intake of 125 mg tolbutamide using liquid chromatography–tandem mass spectrometry. CYP2C9 genotypes were determined by sequencing of exons 3 and 7. Raw plasma and urine data were compared with pharmacokinetic parameters, CYP2C9 genotypes, and data from a study in 23 volunteers with all six CYP2C9*1–*3 combinations who received 500 mg tolbutamide.Results Plasma clearance and tolbutamide plasma concentrations 24 h after drug intake reflected the genotypes: 0.85 l/h and 1.70 µg/ml (95% confidence interval, CI, 0.80–0.89 l/h and 1.50–1.90 µg/ml) for CYP2C9*1 homozygotes (n=15), 0.77 l/h and 2.14 µg/ml (95%CI, 0.67–0.88 l/h and 1.64–2.63 µg/ml) for *1/*2 genotypes (n=7), 0.60 l/h and 3.13 µg/ml (95%CI, 0.58–0.62 l/h and 2.68–3.58 µg/ml) for *1/*3 genotypes (n=3), and 0.57 l/h and 3.27 µg/ml in the single *2/*2 carrier. Natural logarithms of tolbutamide plasma concentrations 24 h after intake correlated to plasma clearance (r²=0.84, P<0.0000001). This correlation was confirmed in the comparison data set (r²=0.97, P<0.0000001).Conclusions A low dose of 125 mg tolbutamide can safely and accurately be used for CYP2C9 phenotyping. As a simple metric for CYP2C9 activity, we propose to determine tolbutamide in plasma 24 h after drug intake.     

Effect of the single CYP2C9*3 allele on pharmacokinetics and pharmacodynamics of losartan in healthy Japanese subjects

Objective Losartan is metabolized to the active carboxylic acid metabolite EXP3174 by CYP2C9. In this study, we determined the effects of the single CYP2C9*3 variant on the pharmacokinetics and pharmacodynamics of losartan.Methods Seven healthy Japanese subjects (CYP2C9*1/*1, n=4 and CYP2C9*1/*3, n=3) were phenotyped with a single dose of losartan (25 mg). Blood and urine samples were collected and assayed for losartan and EXP3174. Blood pressure and pulse rate were also measured using a sphygmomanometer.Results The maximum plasma concentration of EXP3174 was significantly (P<0.05) lower in the CYP2C9*1/*3 (n=3) group than in the CYP2C9*1/*1 (n=4) group. Diastolic blood pressure in the CYP2C9*1/*1 group, but not that in the CYP2C9*1/*3 group except for at 6 h and 8 h, was reduced from 1.5 h to 12 h compared with the baseline level. Systolic blood pressure in the CYP2C9*1/*1 group, but not that in the CYP2C9*1/*3 group, was reduced from 1 h to 12 h compared with the baseline level. The metabolic ratio (MR) of EXP3174 concentration to the losartan concentration in plasma at 6 h post-dosing and the 4-h to 8-h urinary EXP3174/losartan MR were significantly lower in the CYP2C9*1/*3 group than in the CYP2C9*1/*1 group. The plasma 6-h MR and the 4-h to 8-h urinary MR were significantly (P<0.05) correlated with the plasma AUC ratio (AUC_EXP3174/AUC_losartan), with Spearman rank correlation coefficients of 0.75 and 0.89, respectively.Conclusion The single CYP2C9*3 variant reduces the metabolism of losartan and its hypotensive effect. Plasma MR, as well as urine MR, may be useful for phenotyping assays of CYP2C9 activity.     

Influence of CYP2C19 polymorphism on the pharmacokinetics of nelfinavir and its active metabolite

AIMS

This study reports the pharmacokinetics of nelfinavir, its active metabolite, M8, and active moiety (nelfinavir + M8) in volunteers genotyped for CYP2C19 as extensive metabolizer (*1*1; n = 38), heterozygous poor metabolizer (PM) (*1*2; n = 22) and homozygous PM (*2*2; n = 6).

METHODS

Subjects received nelfinavir at normal dose (3.5 days of 1250 mg q12h) or high dose (1250 mg q12h for 3 days and single dose of 3125 mg on day 4). Steady-state plasma samples were analysed by high-performance liquid chromatography/ultraviolet assay to determine pharmacokinetics.

RESULTS

At steady state, the mean C_max was 42% [95% confidence interval (CI) 19, 69] and 63% (95% CI 20, 122) higher, and mean AUC was 51% (95% CI 24, 83) and 85% (95% CI 32, 159) higher for *1*2 and *2*2 compared with *1*1 subjects, respectively. For M8, the mean C_max and AUC were 35% (95% CI 6, 55) and 33% (95% CI −3, 56), respectively, lower for *1*2 compared with *1*1 subjects. M8 was not detectable in *2*2 subjects. The mean C_max and AUC values for the active moiety were higher by 30–35% for the *1*2 and *2*2 compared with *1*1 subjects.

CONCLUSIONS

Mutation in CYP2C19 increased the systemic exposure of nelfinavir and reduced the exposure of M8. No significant differences were noted among the heterozygous (*1*2) and homozygous (*2*2) PMs. These changes are not considered to be clinically relevant and hence the use of nelfinavir does not require prior assessment of CYP2C19 genotype.     

Population pharmacokinetic analysis of tacrolimus in Mexican paediatric renal transplant patients: role of CYP3A5 genotype and formulation

Aims

The aims of this study were (i) to develop a population pharmacokinetic (PK) model of tacrolimus in a Mexican renal transplant paediatric population (n = 53) and (ii) to test the influence of different covariates on its PK properties to facilitate dose individualization.

Methods

Population PK and variability parameters were estimated from whole blood drug concentration profiles obtained at steady-state using the non-linear mixed effect modelling software NONMEM® Version 7.2.

Results

Tacrolimus PK profiles exhibited high inter-patient variability (IPV). A two compartment model with first order input and elimination described the tacrolimus PK profiles in the studied population. The relationship between CYP3A5 genotype and tacrolimus CL/F was included in the final model. CL/F in CYP3A5*1/*1 and *1/*3 carriers was approximately 2- and 1.5-fold higher than in CYP3A5*3/*3 carriers (non-expressers), respectively, and explained almost the entire IPV in CL/F. Other covariates retained in the final model were the tacrolimus dose and formulation type. Limustin® showed markedly lower concentrations than the rest of the formulations.

Conclusions

Population PK modelling of tacrolimus in paediatric renal transplant recipients identified the tacrolimus formulation type as a significant covariate affecting the blood concentrations and confirmed the previously reported significant effect of CYP3A5 genotype on CL/F. It allowed the design of a proposed dosage based on the final model that is expected to help to improve tacrolimus dosing.     

Bioactive Terpenoids and Flavonoids from Daucus littoralis Smith subsp. hyrcanicus Rech.f,an Endemic Species of Iran

Background

Daucus littoralis Smith subsp. hyrcanicus Rech.f. (Apiaceae) is an endemic species in northern parts of Iran where it is commonly named Caspian carrot. The fruits have been used as condiment.

Methods

In a series of in vitro assays, antioxidant (DPPH and FRAP assays), cytotoxic and antimicrobial activities of different extracts of roots and fruits were evaluated for the first time. The separation and purification of the compounds were carried out on the most potent extracts using various chromatographic methods and identified by spectroscopic data (¹H and ¹³C NMR).

Results

The results showed that among the extracts only fruit methanol extract (FME) has significant antioxidant activity (IC₅₀ = 145.93 μg.ml^-1 in DPPH assay and 358 ± 0.02 mmol FeII/g dry extract in FRAP assay). The radical scavenging activity of FME at 400 μg.ml^-1 was comparable with α-tocopherol (40 μg.ml^-1) and with BHA (100 μg.ml^-1) (p > 0.05). FME did not show any toxicity against cancerous and normal cell lines. Fruit ethyl acetate extract (FEE) had cytotoxic activity against breast carcinoma and hepatocellular carcinoma cells (IC₅₀ 168.4 and 185 μg.ml^-1, respectively), while it did not possess antioxidant activity in comparison with α-tocopherol and BHA as standard compounds. Ethyl acetate and methanol extract of fruits showed antimicrobial activity against Staphylococcus aureus (MIC: 3.75 mg.ml^-1) and Candida albicans (MIC: 15.6 and 7.8 mg.ml^-1, respectively). Four terpenoids were isolated form FEE including: β-sitosterol (1), stigmasterol (2), caryophyllene oxide (3), β-amyrin (4). Also, three flavonoids namely quercetin 3-O-β-glucoside (5), quercetin 3-O-β-galactoside (6) and luteolin (7) were isolated from FME.

Conclusion

This study showed that FEE and FME of D. littoralis Smith subsp. hyrcanicus Rech.f. had the highest biological activities which may be correlated with in vitro cytotoxic, antimicrobial and antioxidant activities of terpenoids and flavonoids components of the extracts.     

Gabapentin potentiation of the antiepileptic efficacy of vigabatrin in an in vitro model of epilepsy

1. An enhancement of promoted release of γ-aminobutyric acid (GABA) and a change in GABA-metabolism have been suggested as mechanisms of action of gabapentin. Vigabatrin is supposed to act mainly via inhibition of GABA-transaminase but it also interferes with GABA-release and GABA-uptake. On the basis of these mechanisms of action, a pharmacodynamic interaction of the two antiepileptic drugs could be supposed which might be of relevance in the sense of a rational polypharmacy.
2. To address the aforementioned hypothesis, experiments were carried out on hippocampal slices (n=107) of guinea-pigs (n=70). Epileptiform field potentials (e.f.p.) were induced by omission of magnesium from the bath solution and recorded in the stratum pyramidale of the CA3 region. Gabapentin (30–600 μM; 5.1–102.72 μg ml⁻¹), vigabatrin (50–200 μM, 6.45–25.8 μg ml⁻¹) and the GABA_A-receptor antagonist bicuculline (100 μM) were added to the bath solution for 3 h.
3. Gabapentin, in concentrations up to 600 μM, failed to decrease the repetition rate or duration of e.f.p. (n=19). However, vigabatrin, evoked a dose-dependent reduction of the repetition rate of e.f.p. For a concentration of 100 μM (12.9 μg ml⁻¹) there was a reduction down to 48±5% (mean±s.e.mean) of the initial value within 3 h (n=11). With simultaneous administration of vigabatrin (100 μM) and gabapentin (60 μM) for 3 h (n=15), the repetition rate of e.f.p. decreased down to 8±3%, which is significantly different from the values obtained after administration of 100 μM vigabatrin alone (P<0.0001). Both, the antiepileptic effect of vigabatrin alone and the enhancement by gabapentin were blocked by the GABA_A-receptor antagonist bicuculline (100 μM, n=16).
4. These results demonstrate that gabapentin is able to augment the antiepileptic effects of vigabatrin significantly. It is possible that a change in the GABA-release machinery is induced by vigabatrin which then can be augmented by gabapentin.

     

The efficacy of parecoxib on systemic inflammatory response associated with cardiopulmonary bypass during cardiac surgery

Aims

Cardiopulmonary bypass (CPB) during cardiac surgery is well known to be associated with the development of a systemic inflammatory response. The efficacy of parecoxib in attenuating this systemic inflammatory response is still unknown.

Methods

Patients undergoing elective mitral valve replacement with CPB were assessed, enrolled and randomly allocated to receive parecoxib (80 mg) or placebo. Blood samples were collected in EDTA vials for measuring serum cytokine concentrations, troponin T, creatinekinase myocardial‐brain isoenzyme CK‐MB concentrations and white cell counts.

Results

Compared with the control group, IL‐6 and IL‐8‐values in the parecoxib group increased to a lesser extent, peaking at 2 h after the end of CPB (IL‐6 31.8 pg ml⁻¹ ± 4.7 vs. 77.0 pg ml⁻¹ ± 14.1, 95% CI −47.6, −42.8, P < 0.001; IL‐8 53.6 pg ml⁻¹ ± 12.6 vs. 105.7 pg ml⁻¹ ± 10.8, 95% CI −54.8, −49.4, P < 0.001). Peak concentrations of anti‐inflammatory cytokine IL‐10 occurred immediately after termination of CPB and were higher in the parecoxib group (115.7 pg ml⁻¹ ± 10.5 vs. 88.4 pg ml⁻¹ ± 12.3, 95% CI 24.7, 29.9, P < 0.001). Furthermore, the increase in neutrophil counts caused by CPB during cardiac surgery was inhibited by parecoxib. The increases in serum troponin T and CK‐MB concentrations were also significantly attenuated by parecoxib in the early post‐operative days. Peak serum concentrations of CK‐MB in both groups occurred at 24 h post‐CPB (17.4 μg l⁻¹ ± 5.2 vs. 26.9 μg l⁻¹ ± 6.9, 95% CI −10.9, −8.1, P < 0.001). Peak troponin T concentrations occurred at 6 h post‐bypass (2 μg l⁻¹ ± 0.62 vs. 3.5 μg l⁻¹ ± 0.78, 95% CI −1.7, −1.3, P < 0.001).

Conclusion

Intra‐operative parecoxib attenuated the systemic inflammatory response associated with CPB during cardiac surgery and lowered the biochemical markers of myocardial injury.     

Clinical pharmacology of AMG 181, a gut-specific human anti-α4β7 monoclonal antibody,for treating inflammatory bowel diseases

Aims

AMG 181 pharmacokinetics/pharmacodynamics (PK/PD), safety, tolerability and effects after single subcutaneous (s.c.) or intravenous (i.v.) administration were evaluated in a randomized, double-blind, placebo-controlled study.

Methods

Healthy male subjects (n= 68) received a single dose of AMG 181 or placebo at 0.7, 2.1, 7, 21, 70 mg s.c. (or i.v.), 210 mg s.c. (or i.v.), 420 mg i.v. or placebo. Four ulcerative colitis (UC) subjects (n= 4, male : female 2:2) received 210 mg AMG 181 or placebo s.c. (3:1). AMG 181 concentration, anti-AMG 181-antibody (ADA), α₄β₇ receptor occupancy (RO), target cell counts, serum C-reactive protein, fecal biomarkers and Mayo score were measured. Subjects were followed 3–9 months after dose.

Results

Following s.c. dosing, AMG 181 was absorbed with a median t_max ranging between 2–10 days and a bioavailability between 82% and 99%. C_max and AUC increased dose-proportionally and approximately dose-proportionally, respectively, within the 70–210 mg s.c. and 70–420 mg i.v. ranges. The linear β-phase t_1/2 was 31 (range 20–48) days. Target-mediated disposition occurred at serum AMG 181 concentrations of less than 1 μg ml⁻¹. The PD effect on α₄β₇ RO showed an EC₅₀ of 0.01 μg ml⁻¹. Lymphocytes, eosinophils, CD4+ T cells and subset counts were unchanged. AMG 181-treated UC subjects were in remission with mucosal healing at weeks 6, 12 and/or 28. The placebo-treated UC subject experienced colitis flare at week 6. No ADA or AMG 181 treatment-related serious adverse events were observed.

Conclusions

AMG 181 has PK/PD, safety, and effect profiles suitable for further testing in subjects with inflammatory bowel diseases.     

Serum concentrations of sertraline and N-desmethyl sertraline in relation to CYP2C19 genotype in psychiatric patients

Objective  To investigate the impact of CYP2C19 genotype on serum concentrations of sertraline and N-desmethyl sertraline in psychiatric patients. Methods  Patients treated with sertraline (n = 121) were divided into six subgroups according to CYP2C19 genotype: CYP2C19*17/*17, CYP2C19*1/*17, CYP2C19*1/*1, CYP2C19*17/def, CYP2C19*1/def and CYP2C19def/def (def = allele encoding defective CYP2C19 metabolism, i.e. *2 and *3). Dose-adjusted serum concentrations were compared by linear mixed model analyses using the CYP2C19*1/*1 subgroup as reference. Results  Subgroups carrying one or two alleles encoding defective CYP2C19 metabolism achieved significantly higher mean dose-adjusted serum concentrations of sertraline and N-desmethyl sertraline compared to the CYP2C19*1/*1 subgroup (P < 0.05). The effect of CYP2C19 genotype was expressed as 3.2-fold (sertraline) and 4.5-fold (N-desmethyl sertraline) higher dose-adjusted serum concentrations in the CYP2C19def/def subgroup compared to the CYP2C19*1/*1 subgroup (P < 0.01). The CYP2C19*17 allele had no influence on the dose-adjusted serum concentrations of sertraline and N-desmethyl sertraline. Conclusion  The significantly higher serum concentrations associated with alleles encoding defective CYP2C19 metabolism might be of relevance for the clinical outcome of sertraline treatment.     

Effect of CYP2C19*2 and *17 mutations on pharmacodynamics and kinetics of proton pump inhibitors in Caucasians

AIMS

To investigate the impact of CYP2C19 mutations *2-*6 and *17 on acid-inhibition and pharmacokinetics of lansoprazole (L15), omeprazole (O10, O20) and pantoprazole (P40) in Caucasians.

METHODS

CYP2C19 genotyping for *2–*6 and *17 mutations was assessed in subjects who were H. pylori negative in two randomized crossover trials. The influence of CYP2C19 mutations on single and repeated administration of L15 and O10 (study A) and O20 and P40 (study B) was investigated. Pharmacokinetics and the cumulative percentage of time with intragastric pH above 4 (% > pH 4) were assessed on day 1 and 6.

RESULTS

For study A CYP2C19 genotyping found five *1/*1, four *1/*2, one *1/*17 and one *2/*17. For study B the results were six *1/*1, two *1/*2, six *1/*17, one *2/*2 and one *2/*17. For all PPIs AUC was highest in *2/*2 and lowest in *1/*17. On day 1, all PPIs significantly increased percentage >pH 4 compared with baseline. *1/*1 genotype showed no significant acid-inhibition after L15, O10 and O20. *1/*17 genotype showed no significant acid-inhibition after O20 and P40. *1/*2 genotype showed significant acid-inhibition after L15 and O10. On day 6, all four PPIs showed significantly increased acid-inhibition. *1/*1 and *1/*17 showed a significantly increased percentage > pH 4 after treatment with O20 and P40. However, in *1/*1 subjects percentage > pH 4 was not significantly increased after L15 and O10. *1/*2 genotype showed a significant acid-inhibitory effect after repeated dosing with L15 and O10.

CONCLUSIONS

Caucasian subjects with *1/*1 and *1/*17 genotype need stronger acid-suppression therapy, especially during the first days of treatment or with on-demand therapy.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

• The influence of CYP2C19 on the kinetics and dynamics of omeprazole, lansoprazole and rabeprazole has been studied in Japanese subjects.
• It has been suggested that subjects with *1/*1 genotype might need stronger acid suppression than *1/*2 and *2/*2 subjects. This suggestion comes from data in Japanese subjects and has not been confirmed in Caucasians.
• Furthermore, a novel CYP2C19 mutation, *17, which mainly occurs in Caucasians has been discovered. This mutation has been associated with clinical failure, but its relevance for therapy with PPIs has not been studied yet.

WHAT THIS STUDY ADDS

• In this study, the influence of CYP2C19 on both the pharmacokinetics and dynamics in Caucasian subjects after single and repeated dosing has been investigated.
• This is the first study showing that Caucasian subjects with *1/*1 and *1/*17 mutations need stronger acid-inhibition. In this study three proton pump inhibitors (omeprazole, lansoprazole and pantoprazole, in different doses) were studied of which pantoprazole had not been studied before in this setting, not even in Japanese.