: The purpose of this study was to evaluate the role of sequence variants in the CYP2C8, ABCB1 and CYP3A4 genes and the CYP3A4 phenotype for the pharmacokinetics and toxicity of paclitaxel in ...ovarian cancer patients. Thirty‐eight patients were treated with paclitaxel and carboplatin. The genotypes of CYP2C8*1B, *1C, *2, *3, *4, *5, *6, *7, *8 and P404A, ABCB1 G2677T/A and C3435T, as well as CYP3A4*1B, were determined by pyrosequencing. Phenotyping of CYP3A4 was performed in vivo with quinine as a probe. The patients were monitored for toxicity and 23 patients underwent a more extensive neurotoxicity evaluation. Patients heterozygous for G/A in position 2677 in ABCB1 had a significantly higher clearance of paclitaxel than most other ABCB1 variants. A lower clearance of paclitaxel was found for patients heterozygous for CYP2C8*3 when stratified according to the ABCB1 G2677T/A genotype. In addition, the CYP3A4 enzyme activity in vivo affected which metabolic pathway was dominant in each patient, but not the total clearance of paclitaxel. The exposure to paclitaxel correlated to the degree of neurotoxicity. Our findings suggest that interindividual variability in paclitaxel pharmacokinetics might be predicted by ABCB1 and CYP2C8 genotypes and provide useful information for individualized chemotherapy.
OBJECTIVESTo study the potential endogenous marker of CYP3A activity, 4β-hydroxycholesterol, and its relation to sex and the CYP3A5 geno/haplotypes and compare with CYP3A4/5 catalyzed 3-hydroxylation ...of quinine in the three major races.
METHODSThe plasma concentration of 4β-hydroxycholesterol was measured in healthy Tanzanians (n=138), Swedes (n=161) and Koreans (n=149) by gas chromatography–mass spectrometry. The metabolic ratio of quinine/3-hydroxyquinine in plasma 16-h post dose was determined by high performance liquid chromatography, previously reported in Tanzanians and Swedes, and now also in Koreans. The participants were genotyped for relevant alleles of CYP3A5.
RESULTSThe mean plasma concentrations of 4β-hydroxycholesterol in Koreans, Swedes and Tanzanians were 29.3, 26.8 and 21.9 ng/ml, respectively (P<0.01 between all three populations). Within all three populations there were significant differences in 4β-hydroxycholesterol levels between the CYP3A5 genotypes. Women had higher concentrations than men, but the difference was only significant in Tanzanians (P<0.001) and Koreans (P<0.00001). The quinine/3-hydroxyquinine metabolic ratio was significantly different in all three populations with the highest CYP3A activity in Koreans and the lowest in Tanzanians. Korean women had a lower metabolic ratio than men (P<0.00001). Significant correlations between 4β-hydroxycholesterol and quinine 3-hydroxylation were found in Tanzanians and Koreans.
CONCLUSIONClear differences in the activity of both CYP3A4 and CYP3A5 were shown in the three major human races. Both 4β-hydroxycholesterol and quinine/3-hydroxyquinine metabolic ratio showed a higher CYP3A activity in women than in men. The results give strong evidence that the plasma concentration of 4β-hydroxycholesterol may be used as an endogenous marker of CYP3A activity (CYP3A4+5).
: Cytochrome P450 (CYP) 2C9 is responsible for the metabolism of a number of widely used drugs such as oral anticoagulants, oral antidiabetics and non‐steroidal anti‐inflammatory drugs. The CYP2C9 ...is a genetically polymorphic enzyme. The most common allele is CYP2C9*1, while CYP2C9*2 and CYP2C9*3 are the less‐frequent variants. The activity of the enzyme encoded by either CYP2C9 *2 or *3 variant is lower compared with that of the CYP2C9*1. The metabolism of most of the CYP2C9 substrates decreases in varying degrees in subjects carrying the CYP2C9 *2 or *3 allele. The aim of this study was to investigate the frequencies of the major variants of the CYP2C9 in Saudi Arabians.
Purpose
Imatinib is currently used for the treatment of chronic myeloid leukemia (CML). The main metabolite CGP74588 has similar potency to that of imatinib and is a product of CYP3A4 and CYP3A5 ...metabolism. However, the clinical significance of the metabolism on therapeutic response and pharmacokinetics is still unclear. We designed this study to investigate the role of the CYP3A activity in the response to imatinib therapy.
Methods
Fourteen CML patients were phenotyped for in vivo CYP3A activity using quinine as a probe drug. The plasma concentration ratio of quinine and its CYP3A metabolite was used for assessing CYP3A activity. The patients were divided into complete molecular responders with undetectable levels of
BCR-ABL
transcripts after 12 months of therapy and into partial molecular responders who had failed to achieve a complete molecular response.
Results
Patients that achieved complete molecular response showed significantly (Mann-Whitney U-test,
p
= 0.013) higher in vivo CYP3A activity (median quinine metabolic ratio = 10.1) than patients achieving partial molecular response (median = 15.9).
Conclusions
These results indicate a clinical significance of the CYP3A activity and its metabolic products in CML patients treated with imatinib.
OBJECTIVESTo study the correlation between CYP3A5 genotype and quinine 3-hydroxylation in black Tanzanian and Swedish Caucasians as well as to investigate the interethnic differences in CYP3A ...activity between the two populations.
METHODSTanzanian (n=144) and Swedish (n=136) healthy study participants were given a single oral 250 mg dose of quinine hydrochloride and a 16-h post-dose blood sample was collected. The metabolic ratio of quinine/3-hydroxyquinine was determined in plasma by high-performance liquid chromatography. All the participants were genotyped for the known mutations of CYP3A5, which are relevant for the respective population. Correlation between quinine metabolic ratio and CYP3A5 genotype as well as the interethnic difference in CYP3A activity between the two populations was studied.
RESULTSTanzanians had significantly higher (P<0.0001) mean quinine metabolic ratio (9.5±3.5) than Swedes (7.6±3.1). As expected, the frequency of high CYP3A5 expression alleles was higher in Tanzanians (51%) than in Swedes (7%). The mean±SD quinine metabolic ratio (10.7±3.9) in Tanzanians homozygous for low CYP3A5 expression gene was significantly higher than the corresponding mean metabolic ratio in participants heterozygous (9.5±3.3; P=0.02) or homozygous (8.1±3.1; P=0.002) for high expression CYP3A5 alleles, respectively. A tendency to higher quinine metabolic ratio in Swedes with low expression alleles compared with those with one or two high expression alleles was observed. Tanzanians homozygous for low CYP3A5 expression gene (i.e. only CYP3A4 is expressed) had significantly (P<0.0001) higher quinine metabolic ratio (10.7±3.9) than corresponding Swedes (7.7±3.1).
CONCLUSIONSClear interethnic differences were observed in the activity of CYP3A between Tanzanians and Swedes. A significant association is noted between CYP3A5 genotype and quinine 3-hydroxylation in Tanzanians, indicating a significant contribution of CYP3A5 to total 3A activity. The CYP3A4 catalyzed hydroxylation of quinine (two low CYP3A5 expression alleles) was lower in Tanzanians than in Swedes.
Objectives: Our objectives were (1) to determine whether the drugs caffeine, losartan, omeprazole, debrisoquin (INN, debrisoquine), and quinine can be given simultaneously in low doses as a cocktail ...for the phenotyping of cytochrome P450 (CYP) 1A2, 2C9, 2C19, 2D6, and 3A4, respectively, and (2) to design an administration schedule to give as few sampling occasions as possible.
Methods: Twenty‐four subjects were given oral doses of 100 mg caffeine, 25 mg losartan, 20 mg omeprazole, 10 mg debrisoquin, and 250 mg quinine on separate days. After a washout period of at least 4 days, all drugs were given simultaneously except for quinine, which was given 8 hours after the other drugs. Blood and urine samples were collected to determine parent drug and metabolite concentrations for assessment of phenotyping indices. Any difference between both single and cocktail doses was tested on a log‐normal distribution.
Results: The phenotypic indices of CYP1A2 (paraxanthine/caffeine in 4‐hour plasma), CYP2C9 (losartan/E‐3174 metabolite of losartan in 0‐ to 8‐hour urine), CYP2C19 (omeprazole/5‐hydroxyomeprazole in 3‐hour plasma), and CYP3A4 (quinine/3‐hydroxyquinine in 16‐hour plasma) were not significantly changed when probe drugs were administered alone compared with together, although a tendency toward higher concentrations of losartan was seen during simultaneous administration (95% confidence interval, 0.51–1.002; P = .051). The CYP2D6 phenotypic index (debrisoquin/4‐hydroxydebrisoquin in 0‐ to 8‐hour urine) was significantly changed when drugs were given together (95% confidence interval, 0.45–0.87; P = .007), indicating an inhibition of the debrisoquin metabolism. The within‐subject coefficients of variation (8%‐25%) were much lower than the between‐subject coefficients of variation (34%‐79%).
Conclusions: The administration of drugs together suggests an inhibition of debrisoquin metabolism caused by the concurrent drugs given. By separating debrisoquin from the other cocktail drugs, this method is likely to be used as a tool to phenotype the enzymes CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3A4 with only 2 urinary collections and 2 blood‐sampling occasions.
Clinical Pharmacology & Therapeutics (2003) 73, 517–528; doi: 10.1016/S0009‐9236(03)00050‐X
The antifungal drug ketoconazole (KTZ) is known as an inhibitor of, especially, the CYP3A subfamily, which catalyzes the metabolism of a large variety of drugs. Interactions between KTZ and CYP3A ...substrates have been reported both in vivo and in vitro. Most of them, however, involved the KTZ racemate. KTZ racemate and the separate enantiomers, 2R,4R; 2R,4S; 2S,4S, and 2S,4R, were evaluated for their selectivity in inhibiting alprazolam and quinine metabolism.
The inhibition of alprazolam and quinine metabolism was studied in an in vitro system of human liver microsomes (HLM), recombinant of CYP3A4 and CYP3A5. The concentrations of formed 3-hydroxyquinine and 4- and alpha-hydroxyalprazolam were measured by HPLC and LC-MS, respectively.
Quinine 3-hydroxylation was catalyzed to a similar extent by CYP3A4 and CYP3A5. The formation rate of 4-hydroxyalprazolam was higher than that of alpha-hydroxyalprazolam for each HLM, CYP3A4 and CYP3A5. KTZ racemate and enantiomers showed differential inhibitory effects of quinine and alprazolam metabolism. Quinine metabolism catalyzed by HLM, CYP3A4 and CYP3A5 was potently inhibited by the trans-enantiomer KTZ 2S,4S, with IC(50) value of 0.16 microM for HLM, 0.04 microM for CYP3A4 and 0.11 microM for CYP3A5. The same enantiomer showed the lowest IC(50) values of 0.11 microM for HLM and 0.04 microM for CYP3A5 with respect to alprazoalm 4-hydroxylation and also the same pattern for alprazolamalpha-hydroxylation, 0.13 microM for HLM and 0.05 microM for CYP3A5. Alprazolam metabolism (both alpha- and 4- hydroxylations) catalyzed by CYP3A4 was inhibited potently by the cis-enantiomer KTZ 2S,4R, with IC(50) values of 0.03 microM.
Alprazolam and quinine metabolism is catalyzed by both CYP3A4 and CYP3A5. The present study showed that different KTZ enantiomers inhibit CYP3A4 and CYP3A5 to different degrees, indicating that structural differences among the enantiomers would be related to their inhibitory potency on these two enzymes.
Purpose The study aimed to investigate the effects of Plasmodium falciparum infection on the pharmacokinetics of quinine and its metabolites in pregnant and non-pregnant Sudanese women. Methods In a ...case-control study, nine pregnant and eight non-pregnant Sudanese women infected with P. falciparum were treated with intramuscular artemether. Before being given artemether, they received a single dose of quinine hydrochloride as intravenous infusion. Blood samples were collected frequently and analysed for quinine and its metabolites (phase I). One week later (after clearance of parasitaemia) the quinine part of the protocol was repeated (phase II). Results During phase I, the AUCs (mean ± SD) of quinine and its major metaboplite, 3-hydroxyquinine, in pregnant women were 428.2 ± 132.4 and 27.8 ± 14.1 μmol l⁻¹ h⁻¹ respectively. In non-pregnant women the AUCs of quinine and 3-hydroxyquinine were 517.8 ± 100.0 and 32.3 ± 15.3 μmol l⁻¹ h⁻¹. In pregnant women the mean (90% confidence interval) AUC ratios of phase I to phase II of quinine and 3-hydroxyquinine were 1.6 (0.61, 4.22) and 1.01 (0.18, 5.60). In non-pregnant women, the AUC ratios of phase I to phase II of quinine and 3-hydroxyquinine were 1.93 (1.74, 2.15) and 1.19 (0.95, 1.47). Conclusions Plasmodium falciparum infection significantly increased plasma concentration of quinine in non-pregnant women and showed the same trend in pregnant women.
A sensitive and specific method was developed for quantification of alprazolam and its two metabolites 4-hydroxyalprazolam and α-hydroxyalprazolam in plasma. The work up procedure was solid phase ...extraction. Liquid chromatography–mass spectrometry (LC–MS) was used for separation, detection and quantification of the analytes. The limit of quantitation (LOQ) was 0.05
ng/mL for alprazolam and the two metabolites. The extraction recovery was more than 82% for alprazolam and its metabolites. The within- and between-assay coefficients of variation were in the range of 1.9–17.9%. The method was used for determination of the pharmacokinetics parameters of alprazolam and its two metabolites in healthy Caucasian subjects who ingested 1
mg of alprazolam.
A simple high-performance liquid chromatographic method for the simultaneous analysis of quinine and 3-hydroxyquinine in blood samples dried on filter paper is described. Sample preparation involves ...liquid–liquid extraction with toluene–butanol 75:25 (v/v) followed by evaporation. A reversed-phase liquid chromatography system with fluorescence detection was used. The limit of determination was 10 n
M for both quinine and 3-hydroxyquinine and the recovery varied between 78 and 109%. The within- and between-assay coefficients of variation varied between 2–5% and 4–10%, respectively. No loss of either analyte occurred after storage for 2 months at room temperature or at 37
°C. This method for sampling has advantages that make it of great value for clinical and pharmacokinetic studies especially in remote regions where storage and transportation is problematic.
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