Olanzapine disposition in humans is unrelated to CYP1A2 and CYP2D6 phenotypes

OBJECTIVE: Limited data suggest that CYP1A2 and CYP2D6 are involved in the metabolism of olanzapine. The purpose of this study was to further elucidate the role of these enzymes in the disposition of olanzapine in vivo. METHODS: Seventeen healthy non-smoking male volunteers were included in the study. Five subjects were CYP2D6 poor metabolisers (PMs), and 12 were CYP2D6 extensive metabolisers (EMs). All subjects received a single oral dose of 7.5 mg olanzapine, and serum concentrations were measured for 96 h using gas chromatography. A cross-over study was undertaken in the 12 CYP2D6 EMs who at least 2 weeks before or after the olanzapine dose received a single oral dose of 200 mg caffeine. The concentrations of caffeine and paraxanthine were measured in saliva 10 h after caffeine intake, and the paraxanthine/caffeine ratio was calculated as a measure of CYPIA2 activity. RESULTS: A threefold inter-individual variability in oral clearance (CLoral) and maximum serum concentration (Cmax) of olanzapine was observed and a 2.3-fold inter-individual variability in CYPIA2 activity. There was no significant correlation between CYP1A2 activity and oral clearance of olanzapine (r=-0.19, P=0.56). Moreover, there were no significant differences in any of the olanzapine pharmacokinetic parameters between the CYP2D6 PMs and EMs (CLoral=0.246 l h(-1) kg(-1) and 0.203 l h(-1) kg(-1), respectively, P=0.30). CONCLUSION: Neither CYP1A2 nor CYP2D6 seem to have a dominating role in olanzapine biotransformation after intake of a single dose.     

Olanzapine. Pharmacokinetic and pharmacodynamic profile.

Multicentre trials in patients with schizophrenia confirm that olanzapine is a novel antipsychotic agent with broad efficacy, eliciting a response in both the positive and negative symptoms of schizophrenia. Compared with traditional antipsychotic agents, olanzapine causes a lower incidence of extrapyramidal symptoms and minimal perturbation of prolactin levels. Generally, olanzapine is well tolerated. The pharmacokinetics of olanzapine are linear and dose-proportional within the approved dosage range. Its mean half-life in healthy individuals was 33 hours, ranging from 21 to 54 hours. The mean apparent plasma clearance was 26 L/h, ranging from 12 to 47 L/h. Smokers and men have a higher clearance of olanzapine than women and nonsmokers. After administering [14C]olanzapine, approximately 60% of the radioactivity was excreted in urine and 30% in faeces. Olanzapine is predominantly bound to albumin (90%) and alpha 1-acid glycoprotein (77%). Olanzapine is metabolised to its 10- and 4'-N-glucuronides, 4'-N-desmethylolanzapine [cytochrome P450 (CYP) 1A2] and olanzapine N-oxide (flavin mono-oxygenase 3). Metabolism to 2-hydroxymethylolanzapine via CYP2D6 is a minor pathway. The 10-N-glucuronide is the most abundant metabolite, but formation of 4'-N-desmethylolanzapine is correlated with the clearance of olanzapine. Olanzapine does not inhibit CYP isozymes. No clinically significant metabolic interactions were found between olanzapine and diazepam, alcohol (ethanol), imipramine, R/S-warfarin, aminophylline, biperiden, lithium or fluoxetine. Fluvoxamine, an inhibitor of CYP1A2, increases plasma concentrations of olanzapine; inducers of CYP1A2, including tobacco smoke and carbamazepine, decrease olanzapine concentrations. Orthostatic changes were observed when olanzapine and diazepam or alcohol were coadministered. Pharmacodynamic interactions occurred between olanzapine and alcohol, and olanzapine and imipramine, implying that patients should avoid operating hazardous equipment or driving an automobile while experiencing the short term effects of the combinations. Individual factors with the largest impact on olanzapine pharmacokinetics are gender and smoking status. The plasma clearance of olanzapine generally varies over a 4-fold range, but the variability in the clearance and concentration of olanzapine does not appear to be associated with the severity or duration of adverse effects or the degree of efficacy. Thus, dosage adjustments appear unnecessary for these individual factors. However, dosage modification should be considered for patients characterised by a combination of factors associated with decreased oxidative metabolism, for example, debilitated or elderly women who are nonsmokers.     

Nonparametric expectation maximisation (NPEM) population pharmacokinetic analysis of caffeine disposition from sparse data in adult caucasians: systemic caffeine clearance as a biomarker for cytochrome P450 1A2 activity

OBJECTIVE: To explore the ability of the nonparametric expectation maximisation (NPEM) method of population pharmacokinetic modelling to deal with sparse data in estimating systemic caffeine clearance for monitoring and evaluation of cytochrome P450 (CYP) 1A2 activity. DESIGN AND PARTICIPANTS: Nonblind, single-dose clinical investigation in 34 non-related adult Bulgarian Caucasians (18 women and 16 men, aged between 18 and 62 years) with normal and reduced renal function. METHODS: Each participant received oral caffeine 3 mg/kg. Two blood samples per individual were taken according to the protocol for measuring caffeine plasma concentrations. A total of 67 measured concentrations were used to obtain NPEM estimates of caffeine clearance. Paraxanthine/caffeine plasma ratios were calculated and correlated with clearance estimates. Graphical methods and tests for normality were applied and parametric and nonparametric statistical tests were used for comparison. RESULTS: NPEM median estimates of caffeine absorption and elimination rate constants, k(a) = 4.54 h(-1) and k(el) = 0.139 h(-1), as well as of fractional volume of distribution and plasma clearance, V(S1) = 0.58 L/kg and CL(S1) = 0.057 L/h/kg, agreed well with reported values from more 'data rich' studies. Significant correlations were observed between paraxanthine/caffeine ratios at 3, 8 and 10 hours and clearance (Spearman rank correlation coefficients, r(s), >0.74, p 相似文献   

A pharmacokinetic interaction between carbamazepine and olanzapine: observations on possible mechanism

Objective: Olanzapine is a novel antipsychotic, which is effective against both the positive and negative symptoms of schizophrenia and causes fewer extrapyramidal adverse effects than conventional antipsychotics. The purpose of the present study was to assess the potential for a pharmacokinetic interaction between olanzapine and carbamazepine, since these agents are likely to be used concomitantly in the treatment of manic psychotic disorder. Method: The pharmacokinetics of two single therapeutic doses of olanzapine were determined in 11 healthy volunteers. The first dose of olanzapine (10 mg) was taken alone and the second dose (10 mg) after 2 weeks of treatment with carbamazepine (200 mg BID). Measurement of urinary 6-hydroxycortisol/cortisol excretion was used as an endogenous marker to confirm that induction of CYP3A4 by carbamazepine had occurred. Results: The dose of olanzapine given after a 2-week pre-treatment with carbamazepine was cleared more rapidly than olanzapine given alone. Olanzapine pharmacokinetic values for C_max and AUC were significantly lower after the second dose, the elimination half-life was significantly shorter, and the clearance and volume of distribution were significantly increased. Conclusion: Carbamazepine has been shown to induce several P450 cytochromes including CYP3A4 and CYP1A2. Since CYP1A2 plays a role in the metabolic clearance of olanzapine, the interaction may be attributed to induction of CYP1A2 by carbamazepine, leading to increased first-pass and systemic metabolism of olanzapine. The interaction is not considered to be of clinical significance because olanzapine has a wide therapeutic index, and the changes in plasma concentration of olanzapine are within the fourfold variation that occurs without concern for safety in a patient population. Received: 22 July 1997 / Accepted in revised form: 1 June 1998     

Dextromethorphan to dextrorphan urinary metabolic ratio does not reflect dextromethorphan oral clearance.

Dextromethorphan urinary metabolic ratio is widely used to determine the CYP2D6 phenotype, but its utility to reflect subtle differences in catalytic activity is unclear. We evaluated the capability of dextromethorphan urinary metabolic ratio to predict dextromethorphan oral clearance as a measure of CYP2D6 activity. Data from 10 healthy extensive metabolizers of CYP2D6 were given 30 mg of dextromethorphan hydrobromide orally on two occasions. Blood and urine samples were collected for 72 h. Dextromethorphan and dextrorphan were determined in urine by high-performance liquid chromatography with fluorescence detection and in serum by liquid chromatography-mass spectrometry. The urinary metabolic ratio was very weakly correlated with dextromethorphan oral clearance (r = 0.24; p = 0.04). In contrast, the dextromethorphan oral clearance was highly correlated with the dextromethorphan to dextrorphan area under the concentration-time curve ratio (r = 0.84; p = 0.005) and the 3-h (r = 0.60; p = 0.003), 4-h (r = 0.72, p < 0.001), 6-h (r = 0.67; p < 0.001), and 8-h (r = 0.74; p < 0.001) dextromethorphan to dextrorphan serum ratios. Assuming an effect size of 30%, the number of volunteers required for crossover and cross-sectional studies using the urinary metabolic ratio as the CYP2D6 index was calculated to be 56 and 524, respectively, whereas 14 and 60 subjects are needed if oral clearance is used. Considering the required sample size and the low correlation with oral clearance, urinary metabolic ratio is not recommended as the primary outcome variable in studies requiring the detection of modest changes in CYP2D6 activity.     

Caffeine based measures of CYP1A2 activity correlate with oral clearance of tacrine in patients with Alzheimer''s disease

Aims To study the potential utility of caffeine based probes of CYP1A2 enzyme activity in predicting the pharmokinetics of tacrine in patients with Alzheimer's disease.
Methods The pharmokinetics of a single 40  mg oral dose of tacrine were measured in 19 patients with Alzheimer's disease. Each patient also received 2  mg  kg⁻¹ [¹³C-3-methyl] caffeine orally and had breath and urine samples collected.
Results Tacrine oral clearance (CL   F ⁻¹  kg⁻¹ ), which varied 15-fold among the patients, correlated significantly with the 2  h total production of ¹³CO₂ in breath ( r =0.56, P =0.01), and with each of two commonly used urinary caffeine metabolite ratios: the raxanthine/caffeine ratio' (1,7X+1, 7U)/1,3,7X) ( r =0.76, P =0.0002) and the 'caffeine metabolic ratio' (AFMU+1X+1U)/1, 7U)( r =0.76, P =0.0001).
Conclusions These observations support a central role for CYP1A2 in the in vivo disposition of tacrine and the potential for drug interactions when tacrine treated patients receive known inducers or inhibitors of this enzyme. The magnitude of the correlations we observed, however, are probably not suffcient to be clinically useful in individualizing tacrine therapy.     

Role of the smoking-induced cytochrome P450 (CYP)1A2 and polymorphic CYP2D6 in steady-state concentration of olanzapine

This study investigated whether the smokinginducible cytochrome P450 (CYP) 1A2 and the polymorphic CYP2D6 play significant roles in the metabolism of olanzapine and its clinical effects at steady-state treatment. Caffeine and debrisoquine were used as measures of CYP1A2 and CYP2D6, respectively. After drug therapy for 15 days, the effect of olanzapine on the activities of CYP1A2 and CYP2D6 was also examined. Seventeen psychiatric patients (9 men and 8 women) were orally administered olanzapine, at a mean +/- standard deviation (SD) dosage of 10 mg/d for all smokers (n = 8) and 7.5 +/- 2.5 mg/d (range, 5-10 mg) for nonsmokers (n = 9;p <0.01). The plasma concentration-to-dose (C:D) ratio was closely correlated to the CYP1A2 activity ( s = -0.89;p <0.0001). The mean urinary caffeine indexes of nonsmokers and smokers were 17 +/- 8 and 101 +/- 44, respectively, indicating that smoking had induced a sixfold higher CYP1A2 activity (p <0.0001). Likewise, the olanzapine plasma C:D ratio (ng.mL.mg) was about fivefold lower in smokers (7.9 +/- 2.6) than in nonsmokers (1.56 +/- 1.1;p <0.0001). On day 15 of the antipsychotic therapy, the percentage decrease in Brief Psychiatric Rating Scale (BPRS) total score relative to the predosing score (in the drug-free period) was higher for nonsmokers than for smokers (30.4 +/- 10% vs. 12.5 +/- 14%;p <0.01). Six nonsmokers and three smokers experienced side effects with olanzapine. After 15 days of drug treatment, olanzapine had caused significant (p <0.0001) and substantial CYP1A2 inhibition (by 50%) in comparison with predosing values, and such inhibition can contribute to adverse drug interactions. In conclusion, smoking-induced increased CYP1A2 activity significantly diminished plasma olanzapine concentrations and the antipsychotic effect of the drug. The performance of a simple caffeine test may assist in individualization of the olanzapine dosage.     

Association between CYP1A2 activity and riluzole clearance in patients with amyotrophic lateral sclerosis

AIMS: Riluzole is used in a fixed dosing schedule of 50 mg twice daily to treat patients with amyotropic lateral sclerosis (ALS), one form of motor neurone disease. The large variability in the pharmacokinetics of riluzole may be a factor contributing to its limited therapeutic benefit. Riluzole is assumed to be mainly metabolized by the cytochrome P450 enzyme 1A2 (CYP1A2). The aim of the study was to investigate the relationship between CYP1A2 activity and riluzole clearance with a view to optimize drug treatment. METHODS: A group of 30 ALS patients participated in the study. In each patient the CYP1A2 activity was determined using caffeine as a metabolic probe. Riluzole clearance was estimated from serum drug concentration measurements followed by Bayesian fitting. RESULTS: Riluzole clearance and the serum paraxanthine : caffeine (P/C) ratio showed a positive correlation (r = 0.693; P = 0.0002). Linear regression analysis identified the P/C ratio (beta: 1.16) and height (beta: 0.027) as independent predictors of riluzole clearance (adjusted r2 = 0.369). CONCLUSIONS: The P/C ratio, used as measure of CYP1A2 activity, significantly correlated with the riluzole clearance, although only 37% of the observed variability could be explained.     

Theophylline has no advantages over caffeine as a putative model drug for assessing CYP1A2 activity in humans

Aims The cytochrome P4501A2 (CYP1A2) catalyses the metabolism of a number of clinically used drugs, and thus there is an interest in determining the activity of CYP1A2 in patients before treatment with CYP1A2 substrates. Caffeine is the most commonly used model drug to assess CYP1A2 function, but due to the complex metabolism of caffeine, there is a need for an alternative drug to use as an index of CYP1A2 activity. In this study the CYP1A2 substrate theophylline was tested as a possible alternative to caffeine as a model drug for CYP1A2. Methods Twelve healthy volunteers ingested 200 mg of caffeine, and the caffeine metabolic ratios (CMR), CMR_urine=(AFMU+1MX+1MU)/17DMU and CMR_plasma=17DMX/137TMX were determined 6 h after drug intake. After a period of about 2 months the volunteers ingested 257 mg theophylline and blood samples were drawn and urine was collected during the following 48 h. The oral and partial clearances of theophylline were calculated via N-demethylation and 8-hydroxylation. The theophylline metabolic ratios, 1MU/13DMX and 3MX/13DMX being evaluated as indices of CYP1A2 catalysed N-demethylation and 13DMU/13DMX as an index of partly CYP1A2 catalysed 8-hydroxylation, were estimated in 0–12 h, 0–24 h and 0–48 h urine samples, and in plasma and spot urine samples 6 h after the intake of theophylline. Results The theophylline plasma ratios for the N-demethylation pathways correlated with the oral clearance of theophylline (r_s=0.881-0.934, P<0.001) and with the respective formation clearances of the metabolites (r_s=0.712-0.925, P<0.05). Furthermore, all of the theophylline plasma ratios correlated with the caffeine plasma ratio (r_s=0.645-0.663, P<0.05). None of the caffeine metabolic ratios and none of the 6 h urinary theophylline ratios correlated with the oral or the partial clearances of theophylline (r_s=0.042-0.556, P >0.05). The theophylline 0-12 h urine ratios correlated with the oral clearance of theophylline (r_s=0.677-0.757, P<0.05) and with the respective formation clearances of the metabolites (r_s=0.705-0.750, P<0.05). However, none of the theophylline urine ratios correlated with any of the caffeine metabolic ratios. Conclusions In summary the theophylline 6 h plasma and 0–12 h urine ratios 1MU/13DMX and 3MX/13DMX, both reflecting N-demethylation seem to be predictors of the CYP1A2 mediated metabolism of theophylline, whereas only the plasma ratio correlated with the caffeine plasma 17DMX/137TMX ratio. Thus, it would appear that the plasma theophylline N-demethylation ratios are superior to the urine ratios as indices of CYP1A2 activity. However, because in some individuals the concentrations of theophylline metabolites in plasma were close to the limit of detection, it is concluded that theophylline does not have marked advantages over caffeine as a model drug for assessing CYP1A2 activity.     

Tacrine is not an ideal probe drug for measuring CYP1A2 activity in vivo

AIMS: The aim of the present study was to examine the CYP1A2 substrate tacrine as a possible alternative to caffeine for assessing CYP1A2 activity in vivo. METHODS: Eighteen, healthy, nonsmoking men participated. Each volunteer was tested by caffeine (200 mg orally), and caffeine metabolic ratios were calculated. Subsequently, on two occasions, separated by at least 4 weeks, each volunteer was tested with tacrine (40 mg orally). The apparent oral clearance, partial clearances and different metabolic ratios of tacrine were determined. RESULTS: The median oral clearances of tacrine in the two study periods were 1893 l h-1 (range: 736-3098) and 1890 l h-1 (range: 438-4175), respectively. The interindividual coefficient of variation was 42% and 49%, respectively. The intraindividual coefficients of variation ranged from 0.28% to 64% (median: 13%). In both study periods, the oral clearance of tacrine correlated with the caffeine urinary metabolic ratio. However, only modest magnitudes of correlation were observed (rs: 0.64-0.66, P<0. 01). No tacrine metabolic ratio correlating with the oral clearance of tacrine was found. Conclusion The applicability of tacrine as a probe drug for measuring CYP1A2 activity in vivo appears limited.     

丹参-红花药对配伍前后对大鼠肝药酶亚型CYP1A2、CYP2E1和CYP3A4活性的影响

目的 研究丹参、红花药对配伍前后对大鼠肝药酶亚型CYP1A2、CYP2E1和CYP3A4活性的影响。方法 分别选用咖啡因、氯唑沙宗和咪达唑仑作为CYP1A2、CYP2E1和CYP3A4的探针药物。将大鼠随机分为4组,即空白对照组、丹参（1.2 g生药/kg）组、红花（0.4 g生药/kg）组、丹参（1.2 g生药/kg）+红花（0.4 g生药/kg）组,按上述剂量ig给药7 d。于末次给药后30 min,尾iv探针药物咖啡因、氯唑沙宗和咪达唑仑溶液,在不同的时间点取血进行检测;以甲硝唑为内标,采用HPLC法检测探针药物咖啡因、氯唑沙宗和咪达唑仑的量,评价各药物组对大鼠CYP3A4、CYP2E1和CYP1A2活性的影响。结果 与空白对照组比较,丹参组咖啡因、氯唑沙宗和咪达唑仑的清除率（CL）有所增强,曲线下面积（AUC）减少,其半衰期（t_1/2）有减少趋势,但差异均不显著;红花组咖啡因和氯唑沙宗的CL有所降低,但差异不显著,咪达唑仑的CL显著降低（P<0.01）,氯唑沙宗的AUC增加,但差异不显著,咖啡因和咪达唑仑的AUC明显增加（P<0.05、0.01）;丹参+红花组咖啡因和氯唑沙宗的CL明显降低（P<0.05）,曲线下面积（AUC）明显增加（P<0.05）,其t_1/2有延长趋势,但差异不显著。结论 丹参、红花配伍后对CYP450亚型CYP1A2和CYP2E1有抑制作用,这可能是丹参、红花配伍协同增效的作用机制之一。     

Caffeine as a metabolic probe: a comparison of the metabolic ratios used to assess CYP1A2 activity.

1. Caffeine is widely used as an in vivo probe for CYP1A2; the distribution/activity of this enzyme is reported to be reflected by metabolic ratios. 2. Several metabolic ratios using different combinations of urinary metabolites have been used to measure CYP1A2, with varying conclusions on its distribution. 3. A mathematical comparison of five metabolic ratios claiming to reflect CYP1A2 activity was made using data from 237 healthy volunteers. 4. All five metabolic ratios were symmetrically distributed. The five ratios however, measured at least three different parameters, with no one ratio correlating exactly with any other. 5. Data in the literature claiming to measure CYP1A2 using caffeine may reflect other parameters. 6. The complex metabolism of caffeine together with different parameters controlling the renal clearance of each metabolite, makes the use of urinary metabolic ratios an inaccurate probe for assessing the distribution of CYP1A2 activity in populations.     

Phenytoin metabolic ratio: a putative marker of CYP2C9 activity in vivo

CYP2C9 mediates the oxidative metabolism of approximately 10% of drugs, some of which are characterized by a narrow therapeutic index. We aimed to validate genotype method and phenotype methodology, for evaluation of CYP2C9 activity in vivo. Thirty-one healthy subjects (22 male) received a single 300 mg dose of phenytoin. Blood was drawn periodically and urine was collected at intervals for 96 h. Plasma phenytoin and 5-(4-hydroxyphenyl)-5-phenylhydantoin (p-HPPH) and urine S and R enantiomers of p-HPPH were determined by high-performance liquid chromatography. CYP2C9 genotyping was obtained by polymerase chain reaction followed by digestion with Sau96I and StyI for the identification of CYP2C9*2 and CYP2C9*3, respectively. Eighteen subjects were CYP2C9*1 homozygous, seven were CYP2C9*2 heterozygous, four were CYP2C9*3 heterozygous, one was CYP2C9*2 homozygous and one was compound CYP2C9*2/CYP2C9*3 heterozygous. The allele frequencies of CYP2C9*1, CYP2C9*2 and CYP2C9*3 were 0.76 [95% confidence interval (CI) 0.73-0.79], 0.16 (95% CI 0.13-0.19) and 0.08 (95% CI 0.05-0.11), respectively. The CYP2C9-mediated production of (S)-p-HPPH represented the major metabolic pathway of phenytoin biotransformation as its excretion accounted for 95.6 + 0.9% of 'total' p-HPPH excretion over the 96 h collection interval. Phenytoin metabolic clearance to produce (S)-p-HPPH (PMC), correlated significantly with (S)-p-HPPH (or 'total' p-HPPH) content in 0-8, 0-12 and 0-24 urine collections (r = 0.88, 0.85 and 0.89, respectively) and with phenytoin metabolic ratio (PMR) defined as the ratio of urine (S)-p-HPPH (or 'total' p-HPPH) to mid-interval plasma phenytoin (r = 0.90, 0.88 and 0.94, respectively). PMC and PMR exhibited a gene-dose effect so that the highest and lowest values were noted in homozygous subjects CYP2C9*1 and subjects carrying two defective alleles, respectively, whereas heterozygous subjects had intermediate values. CYP2C9 genotyping and several phenytoin metabolic indices are correlated with CYP2C9 activity in vivo. The utility of phenytoin to predict the metabolism of other CYP2C9 substrates justifies further evaluation.     

Dose-dependent alternations in the pharmacokinetics of olanzapine during coadministration of fluvoxamine in patients with schizophrenia

Olanzapine, an atypical antipsychotic agent, is a substrate of the cytochrome P4501A2 (CYP1A2) enzyme. Administration of a potent CYP1A2 inhibitor (eg, fluvoxamine) may alter the pharmacokinetics of olanzapine. This study investigated the pharmacokinetic interactions between olanzapine and fluvoxamine in patients with schizophrenia. Ten male smokers were administrated a single dose of olanzapine 10 mg at baseline, followed by 2 weeks of fluvoxamine 50 mg/day and another 2 weeks of fluvoxamine 100 mg/day. Olanzapine 10 mg was given at day 10 during each fluvoxamine treatment. After pretreatment with fluvoxamine, the area under the curve, maximal plasma concentration, and half-time of olanzapine were significantly increased by 30% to 55%, 12% to 64%, and 25% to 32%, respectively. Volume of distribution and apparent clearance were significantly reduced by 4% to 26% and 26% t O 38%, respectively, after administration of fluvoxamine. Increases in area under the plasma concentration-time curve from time 0 to infinity appear to be dose dependent. Presumably, altered olanzapine pharmacokinetics are attributed to the inhibition of CYP1A2. Patients treated with the combination of olanzapine and fluvoxamine should be monitored carefully.     

Effects of phenothiazine neuroleptics on the rate of caffeine demethylation and hydroxylation in the rat liver

The primary metabolic pathways of caffeine are 3-N-demethylation to paraxanthine (CYP1A2), 1-N-demethylation to theobromine and 7-N-demethylation to theophylline (CYP1A2 and other enzymes), and 8-hydroxylation to 1,3,7-trimethyluric acid (CYP3A). The aim of the present study was to investigate the influence of phenothiazine neuroleptics (chlorpromazine, levomepromazine, thioridazine, perazine) on cytochrome P-450 activity measured by caffeine oxidation in rat liver microsomes. The obtained results showed that all the investigated neuroleptics competitively inhibited caffeine oxidation in the rat liver, though their potency to inhibit particular metabolic pathways was not equal. Levomepromazine exerted the most potent inhibitory effect on caffeine oxidation pathways, the effect on 8-hydroxylation being the most pronounced. This indicates inhibition of CYP 1 A2 (inhibition of 3-N- and 1-N-demethylation; Ki = 36 and 32 microM, respectively), CYP3A2 (inhibition of 8-hydroxylations; Ki = 20 microM), and possibly other CYP isoenzymes (inhibition of 7-N-demethylation; Ki = 58 microM) by the neuroleptics. The potency of inhibition of caffeine oxidation by perazine was similar to levomepromazine. Thioridazine was a weaker inhibitor of caffeine 3-N- and 7-N-demethylation, while chlorpromazine was weaker in inhibiting caffeine 1-N- and 7-N-demethylation, compared to levomepromazine. In summary, the obtained results showed that all the investigated neuroleptics had a broad spectra of CYP inhibition in the rat liver. The isoenzymes CYP1A2 and CYP3A2 were distinctly inhibited by all the investigated neuroleptics, while other CYP isoenzymes (CYP2B and/or 2E1) by perazine and levomepromazine. The CYP3A2 inhibition was most pronounced. (Ki = 20-40 microM).     

Simultaneous assessment of CYP3A4 and CYP1A2 activity in vivo with alprazolam and caffeine

Alprazolam (ALP) and caffeine (CAF) were suggested as probe drugs for the activities of CYP3A4 and CYP1A2, respectively. We investigated the disposition of oral ALP (1 mg) and CAF (100 mg) in 17 normal volunteers to establish and validate a procedure for the simultaneous assessment of CYP3A4 and CYP1A2 enzyme activity. Nine received ALP alone, ALP and CAF and CAF alone in an open three-way crossover study to test for pharmacokinetic interaction. Four received ALP after a 2-day pretreatment with ketoconazole, an inhibitor of CYP3A4, and four normal volunteers received ALP after 4 days of rifampin, an inducer of CYP3A4. AUC values of ALP and CAF administered alone were not different from AUC values when both drugs were administered combined, indicating that there is no metabolic interaction. The ratio formed of paraxanthine and CAF correlated significantly with systemic CAF clearance at 3, 4, 6, 8, 10 and 24 h. There was a strong correlation between AUC values of ALP and CAF and the plasma concentration obtained 6, 8, 10, or 24 h after ingestion of the drug. Ketoconazole and rifampin pretreatment significantly changed AUC values of ALP (mean AUC values in microg/l h: ALP = 242.2, ALP + ketoconazole = 426.2, ALP + rifampin = 28.4, ANOVA F = 17.7, P < 0.001). We conclude that ALP and CAF can be administered simultaneously for the assessment of CYP activity. Plasma concentrations 6, 8, 10, and 24 h after drug ingestion reflect AUC of ALP and CAF and therefore in-vivo CYP3A4 and CYP1A2 activity, respectively.     

Determination of CYP1A2 and NAT2 phenotypes in human populations by analysis of caffeine urinary metabolites.

The wide variations in urinary bladder and colo-rectal cancer incidence in humans have been attributed in part to metabolic factors associated with exposure to carcinogenic aromatic and heterocyclic amines. Cytochrome P-4501A2 (CYP1A2), which catalyses N-oxidation, and acetyltransferase (NAT2) which catalyses N- and O-acetylation, both appear to be polymorphically distributed in human populations; and slow and rapid NAT2 phenotypes have been implicated as risk factors for these cancers. Caffeine has also been shown to undergo 3-demethylation by CYP1A2, and it is further acetylated to 5-acetylamino-6-formylamino-3-methyluracil (AFMU) by the polymorphic NAT2. In this report, we describe a metabolic phenotyping procedure that can be used to determine concomitantly the hepatic CYP1A2 and NAT2 phenotypes. For the NAT2 phenotype, we confirm the valid use of the urinary molar ratio of AFMU/1-methylxanthine, even in alkaline urines. For the CYP1A2 phenotype, the urinary molar ratio of [1,7-dimethylxanthine + 1,7-dimethyluric acid]/caffeine, taken at 4-5 h after caffeine ingestion, was identified from pharmacokinetic analyses of 12 subjects as being better correlated (r = 0.73; p = 0.007) with the rate constant for caffeine 3-demethylation than other previously suggested ratios. This procedure was then used to determine the CYP1A2 phenotype in subjects from Arkansas (n = 101), Italy (n = 95), and China (n = 78). Statistical and probit analyses of nonsmokers indicated that the CYP1A2 activity was not normally distributed and appeared trimodal. This trimodality allowed arbitrary designation of slow, intermediate, and rapid phenotypes, which ranged from 12-13% slow, 51-67% intermediate, and 20-37% rapid, in the different populations. A reproducibility study of 13 subjects over a 5 day or 5 week period showed that, with one exception, intraindividual variability did not alter this CYP1A2 phenotypic classification. Induction of CYP1A2 by cigarette smoking was also confirmed by the increased caffeine metabolite ratios observed in the Arkansas and Italian smokers (blonde tobacco). However, Italian smokers of black tobacco and Chinese smokers did not appear to be induced. Furthermore, probit analyses of Arkansas and Italian blonde tobacco smokers could not discriminate between phenotypes, apparently as a consequence of enzyme induction.     

Lack of Effect of Olanzapine on the Pharmacokinetics of a Single Aminophylline Dose in Healthy Men

Study Objective . To test whether olanzapine, an atypical antipsychotic, is an inhibitor of cytochrome P450 (CYP) 1A2 activity, we conducted a drug interaction study with theophylline, a known CYP1A2 substrate. Design . Two-way, randomized, crossover study. Setting . Clinical research laboratory. Subjects . Nineteen healthy males (16 smokers, 3 nonsmokers). Interventions . Because the a priori expectation was no effect of olanzapine on theophylline pharmacokinetics, a parallel study using cimetidine was included as a positive control. In group 1, 12 healthy subjects received a 30-minute intravenous infusion of aminophylline 350 mg after 9 consecutive days of either olanzapine or placebo. In group 2, seven healthy subjects received a similar aminophylline infusion after 9 consecutive days of either cimetidine or placebo. Measurements and Main Results . Concentrations of theophylline and its metabolites in serum and urine were measured for 24 and 72 hours, respectively. Plasma concentrations of olanzapine and its metabolites were measured for 24 hours after the next to last dose and 168 hours after the last olanzapine dose. Olanzapine did not affect theophylline pharmacokinetics. However, cimetidine significantly decreased theophylline clearance and the corresponding formation of its metabolites. Urinary excretion of theophylline and its metabolites was unaffected by olanzapine but was reduced significantly by cimetidine. Steady-state concentrations of olanzapine (15.3 ng/ml), 10-N-glucuronide (4.9 ng/ml), and 4′-N-desmethyl olanzapine (2.5 ng/ml) were observed after olanzapine 10 mg once/day and were unaffected by coadministration of theophylline. Conclusion . As predicted by in vitro studies, steady-state concentrations of olanzapine and its metabolites did not affect theophylline pharmacokinetics and should not affect the pharmacokinetics of other agents metabolized by the CYP1A2 isozyme.     

Novel olanzapine analogues presenting a reduced H1 receptor affinity and retained 5HT2A/D2 binding affinity ratio

ABSTRACT: BACKGROUND: Olanzapine is an atypical antipsychotic drug with high clinical efficacy, but which can cause severe weight gain and metabolic disorders in treated patients. Blockade of the histamine 1 (H1) receptors is believed to play a crucial role in olanzapine induced weight gain, whereas the therapeutic effects of this drug are mainly attributed to its favourable serotoninergic 2A and dopamine 2 (5HT2A/D2) receptor binding affinity ratios. RESULTS: We have synthesized novel olanzapine analogues 8a and 8b together with the already known derivative 8c and we have examined their respective in vitro affinities for the 5HT2A, D2, and H1 receptors. CONCLUSIONS: We suggest that thienobenzodiazepines 8b and 8c with lower binding affinity for the H1 receptors, but similar 5HT2A/D2 receptor binding affinity ratios to those of olanzapine. These compounds may offer a better pharmacological profile than olanzapine for treating patients with schizophrenia.