Cortisol in the CSF of depressed and suicidal patients.

Cortisol concentrations in CSF were measured by radioimmunoassay in healthy controls, depressed patients, patients who had attempted suicide but were not depressed, and obsessive-compulsive patients. The factors that contributed most to the variance in CSF cortisol levels were a diagnosis of depression, height, and important life changes during the six months preceding the investigation. Depression was by far the most important factor. The depressed patients had significantly higher CSF cortisol levels than the controls. In obsessive-compulsive and depressed patients treated with clomipramine hydrochloride, the levels were significantly correlated with mean urinary cortisol excretion. Of the three monoamine metabolites measured, only 5-hydroxy-indoleacetic acid level was weakly correlated with CSF cortisol level. This correlation was confined to the depressed patients and could be accounted for by the common correlation with height.

A methodological investigation on the estimation of the S-mephenytoin hydroxylation phenotype using the urinary S/R ratio.

After a single oral dose of racemic mephenytoin the S/R ratio in urine can be used to phenotype extensive (EM) and poor metabolizers (PM) of S-mephenytoin. We confirmed the increased S/R ratio by storage time in EM because of the hydrolysis of a conjugate of S-mephenytoin excreted in EM, but not in PM. The S/R ratio in the 0-8 h urine increased 8- to 127-fold (from 0.22 +/- 0.16 to 9.9 +/- 11.3) after acid treatment of urine from 30 EM, but there was no effect of acid in that of 12 PM. We suggest that the phenotype of mephenytoin in combination with debrisoquine can be determined in the 0-8 h urine by estimating the mephenytoin S/R ratio before and after acid treatment.

An S-mephenytoin cysteine conjugate identified in urine of extensive but not of poor metabolizers of S-mephenytoin.

A conjugate of S-mephenytoin excreted in urine of extensive but not of poor metabolizers of S-mephenytoin has previously been reported. This conjugate, which is easily hydrolysed back to S-mephenytoin, has now been isolated and identified in urine from one extensive metabolizer after a single dose of 100 mg racemic mephenytoin. High performance liquid chromatography purification, followed by gas chromatographic, mass spectrometric and amino acid analyses showed that the isolated compound is a cysteine conjugate of S-mephenytoin. The significant mass spectrometric ions have been confirmed in three additional extensive metabolizers of S-mephenytoin, but were not detectable in urine from three poor metabolizer subjects. The exact structure of the conjugate is unknown, but we suggest that an S-N bond between cysteine and S-mephenytoin is formed via an oxidative radical mechanism catalyzed by CYP2C19.

Use of omeprazole as a probe drug for CYP2C19 phenotype in Swedish Caucasians: comparison with S-mephenytoin hydroxylation phenotype and CYP2C19 genotype.

A single oral dose of omeprazole (20 mg) was given orally to 160 healthy Caucasian Swedish subjects and tested as a probe for CYP2C19. The study was nonrandomized and included seven subjects previously classified as poor metabolizers (PM) of S-mephenytoin. The ratio between the plasma concentrations of omeprazole and hydroxyomeprazole (metabolic ratio; MR) was determined by HPLC in a blood sample drawn 3 h after drug intake. In 17 subjects the test was repeated and the MRs of omeprazole on the two occasions were correlated (rs = 0.85; p < 0.0001). There was a significant correlation between the MR of omeprazole and the S/R mephenytoin ratio among 141 subjects, in whom both ratios were determined (rs = 0.63, p < 0.001). All seven PMs of S-mephenytoin had higher MRs of omeprazole (7.1-23.8) than extensive metabolizers (EM) (0.1-4.9). All 160 subjects and another 15 Caucasian Swedish PMs previously phenotyped with mephenytoin were analysed with respect to the presence of the CYP2C19m1 allele by PCR amplification of the intron 4/exon 5 junction followed by Sma I digestion. EMs heterozygous for the CYP2C19m1 gene had MRs of omeprazole and S/R ratios of mephenytoin that were higher than those of subjects who were homozygous for the wild-type allele (p = 0.0001). Nineteen of the 22 PMs were homozygous for the CYP2C19m1 gene. Three were heterozygous for this allele. Thus, 41 of the 44 alleles (93%) of PMs were defective CYP2C19m1. One of the remaining three PM alleles was subsequently found to contain the CYP2C19m2 mutation, which has earlier been shown to be associated with the PM phenotype in Oriental populations. In conclusion, the phenotype determined by omeprazole correlated with that of mephenytoin, and was in good agreement with the genotype.

Effects of thioridazine, an inhibitor of CYP2D6, on the steady-state plasma concentrations of the enantiomers of mianserin and its active metabolite, desmethylmianserin, in depressed Japanese patients.

The antidepressant mianserin is administered as a racemate of the S(+)- and R(-)-enantiomers. Previous in-vitro studies have suggested that CYP2D6 is involved in the stereoselective metabolism of mianserin and its active metabolite, desmethylmianserin. To determine a role for CYP2D6 in vivo, the effects of thioridazine, an inhibitor of CYP2D6, on the steady-state plasma concentrations of the enantiomers of mianserin and desmethylmianserin were examined in 13 depressed Japanese patients. All patients were taking 30 mg of racemic mianserin at bedtime for 8-50 days. Thioridazine (40 mg/day) was coadministered for 1 week, and blood samplings were performed before and after thioridazine coadministration, 12 h after bedtime dosing. Plasma concentrations of the enantiomers of mianserin and desmethylmianserin were measured by HPLC, and the CYP2D6 genotype was determined by allele-specific PCR analysis. Thioridazine significantly increased plasma concentration of S(+)-mianserin (mean SD: 78.2 +/- 35.0 vs. 150.8 +/- 48.7 nM, P < 0.001), but not R(-)-mianserin (39.8 +/- 21.2 vs. 39.5 +/- 20.6 nM, NS). Thioridazine also significantly increased plasma concentrations of both S-desmethylmianserin (11.9 +/- 2.8 vs. 24.4 +/- 10.7 nM, P < 0.01) and R-desmethylmianserin (42.6 +/- 28.4 vs. 115.6 +/- 36.9 nM, P < 0.001). One patient homozygous for the defective allele CYP2D6*5 had the second highest and highest plasma concentrations of S(+)-mianserin and R-desmethylmianserin, respectively, before thioridazine coadministration, and exhibited little increase in plasma concentration of the drugs after thioridazine coadministration. These results suggest that thioridazine specifically inhibits the metabolism of S(+)-mianserin and R-desmethylmianserin, probably through inhibition of CYP2D6, but not R(-)-mianserin.

CYP2C19 genotype and phenotype determined by omeprazole in a Korean population.

Omeprazole (20 mg orally) was given to 103 healthy Korean subjects and blood was taken 3 h after administration. The plasma concentration ratio of omeprazole and hydroxyomeprazole, used as an index of CYP2C19 activity, was bimodally distributed. Thirteen subjects (12.6%) were identified as poor metabolizers (PMs) with an omeprazole hydroxylation ratio of 6.95 or higher. Among the 206 CYP2C19 alleles, CYP2C19*2 and CYP2C19*3 were found in 43 alleles (21%) and 24 alleles (12%), respectively. Twelve subjects (12%) carried two defect alleles (*2/*2, *2/*3 or *3/*3), 43 subjects (42%) were heterozygous for a mutated (*2 or *3) and a wild type (*1) allele, and the remaining 48 subjects (47%) were homozygous for the wild type allele. The distributions of the metabolic ratio between these three genotype groups were significantly different (Kruskal-Wallis test: p < 0.0001). The genotypes of 19 additional Korean PMs has been identified in a previous mephenytoin study. From a total of 32 PMs, 31 were genotypically PMs by analysis of the CYP2C19*2 and *3 alleles and only one PM subject was found to be heterozygous for the *1 and *2 alleles. At present it cannot be judged whether this subject has a defective allele with a so-far unidentified mutation or a true wild type allele. We thus confirm a high incidence (12.6%) of PMs of omeprazole in Koreans and of the 32 Korean PMs 97% could be identified by the genotype analysis.

Single-dose kinetics and metabolism of carbamazepine-10,11-epoxide.

Carbamazepine-(CBZ)-10,11-epoxide (CBZ-E) was found to decompose in gastric juice in vitro. An antacid did not affect the bioavailability of single CBZ doses given to three subjects and was therefore used to neutralize gastric juice when administering CBZ-E. CBZ-E was given orally as a suspension in two single doses ranging from 10 to 200 mg to each of four healthy subjects. Plasma concentrations of CBZ and CBZ-E were determined with high-performance liquid chromatography. Plasma concentrations and urinary excretion of the end metabolite trans-10,11-dihydroxy-10,11-dihydro-CBZ (trans-CBZ-diol) were measured by mass fragmentography. After dosing with CBZ-E, peak plasma concentrations of the parent compound were reached within 2 hr. Urinary recovery of trans-CBZ-diol was 90 +/- 11% (mean +/- SD) of the dose, indicating almost complete absorption. Plasma kinetics of the epoxide fitted an open one-compartment model with elimination half-lifes (t 1/2s) of 6.1 +/- 0.9 hr. Clearance was 89 +/- 25 ml x kg-1 x hr-1. The urinary excretion t 1/2 of the trans-CBZ-diol was 12.4 +/- 0.9 hr, which is longer (P less than 0.001) than the epoxide plasma t 1/2. There was no indication of dose-dependent kinetics of the epoxide. After 200 mg CBZ to the same subjects, plasma CBZ t 1/2 was 26.0 +/- 4.6 hr and clearance was 23.4 +/- 4.6 ml x kg -1 x hr -1. Of the CBZ dose, 20.5 +/- 2.9% was excreted as the trans-CBZ-diol, which gives an estimate of the percentage of CBZ that is metabolized by the epoxide-diol pathway in healthy subjects. These observations provide a basis for the administration of CBZ-E in patients to assess its clinical effects.

No sex-related differences but significant inhibition by oral contraceptives of CYP2C19 activity as measured by the probe drugs mephenytoin and omeprazole in healthy Swedish white subjects.

BACKGROUND: Although it is known that the use of oral contraceptives inhibits oxidative drug metabolism, there is little information regarding their effect on CYP2C19 activity. Moreover, earlier reports suggest that there may be differences in CYP2C19 activity between men and women. OBJECTIVE: We sought to assess the effect of sex and intake of oral contraceptives on CYP2C19 activity as measured by the probe drugs mephenytoin and omeprazole. METHODS: To determine CYP2C19 activity in white Swedish subjects, 644 subjects previously phenotyped with mephenytoin and 175 subjects phenotyped with omeprazole were investigated. The 8-hour urinary mephenytoin S/R ratio after ingestion of 100 mg mephenytoin and the plasma concentration ratio of omeprazole/hydroxyomeprazole at 3 hours after ingestion of 20 mg omeprazole were used as measures of CYP2C19 activity. Differences in these ratios and in their frequency distributions were then examined among women with and without oral contraceptives and men. In addition, nearly all subjects in the omeprazole group had been genotyped with regard to the CYP2C19*2 (ml) allele. Subjects homozygous for the CYP2C19*2 allele were excluded from the study. RESULTS: The median mephenytoin S/R ratio was 2.5-fold higher in the subgroup of women taking oral contraceptives compared with either women not taking oral contraceptives (P < .001) or men (P < .001). Similarly, the mean omeprazole/hydroxyomeprazole ratio was twice as high in the oral contraceptive group compared with women not taking oral contraceptives (P < .001) or men (P < .001). However, no differences were evident between women not taking oral contraceptives and men in either the mephenytoin group (P = .48) or the omeprazole group (P = .77). The oral contraceptive-induced inhibitory effect on CYP2C19 activity was similar between the CYP2C19*1/*1 and *1/*2 genotypes, and they were independent of age. CONCLUSIONS: Intake of oral contraceptives significantly inhibits CYP2C19 activity, but there is no true sex-related difference in CYP2C19 activity in healthy, white, Swedish subjects.

Inhibition of the sulfoxidation of omeprazole by ketoconazole in poor and extensive metabolizers of S-mephenytoin.

BACKGROUND: The metabolism of omeprazole includes hydroxylation catalyzed by CYP2C19 and, to a minor extent, sulfoxidation, presumably by CYP3A4. Sulfoxidation may be the predominant pathway in individuals devoid of the genetically determined CYP2C19 activity. Ketoconazole is a known CYP3A4 inhibitor in daily doses from 200 to 400 mg. In this study ketoconazole was used as a probe to investigate the extent to which CYP3A4 is involved in omeprazole metabolism in vivo. METHODS: A single oral 20 mg dose of omeprazole before and after four daily doses of 200, 100, or 50 mg ketoconazole was given to 10 healthy subjects, previously phenotyped as poor or extensive metabolizers of S-mephenytoin. Concentrations of omeprazole, 5-hydroxyomeprazole, omeprazole sulfone, and ketoconazole were analyzed with reversed-phase HPLC methods in plasma samples collected repeatedly for 12 hours after dosing. RESULTS: After intake of 20 mg omeprazole with 0, 50, 100, and 200 mg ketoconazole, mean values for omeprazole sulfone area under the plasma concentration versus time curve from 0 to 6 hours [AUC(0-6)] were 482, 206, 167, and < 100 nmol/L.hr in extensive metabolizers and 3160, 2430, 937, and 534 nmol/L.hr in poor metabolizers, respectively. Mean omeprazole AUC(0-6) increased from 1660 to 2265 nmol/L.hr in extensive metabolizers and from 7715 to 15319 nmol/L.hr in poor metabolizers after intake of 200 mg ketoconazole. CONCLUSIONS: An oral daily dose of 100 to 200 mg ketoconazole is sufficient to provide a marked inhibition of the formation of the omeprazole sulfone in both extensive and poor metabolizers and leads to a doubling of omeprazole levels in poor metabolizers, whereas 50 mg ketoconazole provides only partial inhibition. We concluded that CYP3A4 catalyzes the sulfoxidation of omeprazole and that this is the predominant metabolic pathway of omeprazole in poor metabolizers of S-mephenytoin.

Enantioselective hydroxylation of omeprazole catalyzed by CYP2C19 in Swedish white subjects.

Stereoselective disposition of omeprazole and its formed 5-hydroxy metabolite were studied in five poor metabolizers and five extensive metabolizers of S-mephenytoin. After a single oral dose of omeprazole (20 mg), the plasma concentrations of the separate enantiomers of the parent drug and the 5-hydroxy metabolite were determined for 10 hours after drug intake. In poor metabolizers, the area under the plasma concentration versus time curve [AUC(0-8)] of (+)-omeprazole was larger and that of the 5-hydroxy metabolite of this enantiomer was smaller than the AUC(0-8) values in extensive metabolizers (p < 0.001). The mean AUC(0-8) of the (-)-enantiomer of omeprazole was also higher in poor metabolizers than in extensive metabolizers, but only 3.1-fold compared with 7.5-fold for (+)-omeprazole. The rate of formation of the hydroxy metabolite from (-)-omeprazole was low and not significantly different in poor and extensive metabolizers. These results show that (+)-omeprazole is to a major extent hydroxylated by CYP2C19. Also (-)-omeprazole may partly be metabolized by this enzyme but is mainly metabolized by another enzyme, presumably CYP3A4, to the achiral sulfone metabolite. The plasma concentration ratio of omeprazole to 5-hydroxyomeprazole obtained 3 hours after the drug intake has been used to distinguish between extensive and poor metabolizer phenotypes. With use of the ratio between the (+)-enantiomers of the parent drug and the metabolite, a better discrimination between phenotypes was obtained. The ratio between the (-)-enantiomers also separated the phenotypes but was less discriminatory. For the future, measurement of total concentrations will suffice for phenotyping.

Autoinduction of carbamazepine metabolism in children examined by a stable isotope technique.

Autoinduction of carbamazepine (CBZ) metabolism was investigated in 3 children (10 to 13 yr old) using tetradeuterium-labeled CBZ (CBZ-D4). Prior to treatment, CBZ and CBZ-D4 given as a mixture had almost identical kinetics in each patient. During maintenance therapy with CBZ, part of the CBZ was exchanged for CBZ-D4 on 3 occasions. The clearance of CBZ-D4 given on the second day of therapy was 0.036 +/- 0.003 1 . kg-1 . hr-1, whereas it had been 0.028 +/- 0.003 before treatment. After 17 to 32 days of treatment, clearance doubled (0.056 +/- 0.010) but during the next 4 mo there was no further increase, indicating that the autoinduction was complete within 1 mo. As a corollary there was a decrease in steady-state plasma levels.

Techniques for plasma protein binding of demethylchlorimipramine.

The cerebrospinal fluid (CSF) and plasma levels of demethylchlorimipramine (DMCI) were determined during treatment of depression or obsessive-compulsive disorders with chlorimipramine. In 18 patients the mean CSF/plasma ratio of DMCI was 2.6% +/- 0.7 SD with fourfold variation (1.1% to 4.0%). In spite of this variation, the levels in CSF and plasma at steady state correlated closely (r = 0.91; p less than 0.001). With equilibrium dialysis for the determination of the protein binding of DMCI, a much higher free fraction was found in patients (8.0 +/- 1.6%) and in control subjects (8.2 +/- 1.4%). It was shown that part of the plasma binding capacity was lost during the incubation. Results obtained by ultrafiltration (3.9 +/- 1.0% unbound drug) were closer to the in vivo results, but this method also had disadvantages; much of the drug was absorbed on the ultrafiltration dialysis membrane. Our results suggest that there is a need for care in the selection of a technique for studies of drug protein binding.

Importance of genetic factors in the regulation of diazepam metabolism: relationship to S-mephenytoin, but not debrisoquin, hydroxylation phenotype.

Single oral 10 mg doses of diazepam and demethyldiazepam were given on different occasions to 16 healthy subjects. The subjects included four poor hydroxylators of debrisoquin and three poor hydroxylators of mephenytoin. There was a correlation between the total plasma clearance of diazepam and demethyldiazepam (rs = 0.83; p less than 0.01). There was no relationship between benzodiazepine disposition and debrisoquin hydroxylation. Poor hydroxylators of mephenytoin had less than half the plasma clearance of both diazepam (p = 0.0008) and demethyldiazepam (p = 0.0001) compared with extensive hydroxylators of mephenytoin. The plasma half-lives were longer in poor hydroxylators than they were in extensive hydroxylators of mephenytoin for both diazepam (88.3 +/- SD 17.2 and 40.8 +/- 14.0 hours; p = 0.0002) and demethyldiazepam (127.8 +/- 23.0 and 59.0 +/- 16.8 hours; p = 0.0001). There was no significant difference in volume of distribution of the benzodiazepines between the phenotypes. This study shows that the metabolism of both diazepam (mainly demethylation) and demethyldiazepam (mainly hydroxylation) is related to the mephenytoin, but not to the debrisoquin, hydroxylation phenotype.

Stereoselective disposition of mianserin is related to debrisoquin hydroxylation polymorphism.

The pharmacokinetics of mianserin and its main metabolite desmethylmianserin were studied in poor and extensive metabolizers of debrisoquin and of S-mephenytoin after a single oral dose of racemic mianserin. The debrisoquin metabolic ratio (MR) correlated significantly with area under the serum concentration-time curves (AUC) for (+/-)-mianserin and (+/-)-desmethylmianserin. Enantioselective high-performance liquid chromatographic analysis of mianserin showed that debrisoquin MR was related to AUC(0-12) for S(+)-mianserin (rs = 0.87; p = 0.001; n = 15) but not for R(-)-mianserin. The ratio between the AUC(0-12) for S(+)-mianserin and that for R(-)-mianserin was higher in poor metabolizers than in extensive metabolizers. Two extremely rapid extensive metabolizer subjects had the lowest mianserin S/R ratios. No differences in the pharmacokinetics of mianserin or desmethylmianserin were found between extensive metabolizers and poor metabolizers of S-mephenytoin. The study shows that the elimination of both mianserin and its main metabolite desmethylmianserin is dependent on CYP2D6 activity. Furthermore, the CYP2D6-dependent elimination of mianserin shows marked enantioselectivity for the more active S(+)-enantiomer of mianserin.

Inhibition of cytochrome P4502D6 activity with paroxetine normalizes the ultrarapid metabolizer phenotype as measured by nortriptyline pharmacokinetics and the debrisoquin test.

BACKGROUND: The ultrarapid metabolizer phenotype of the cytochrome P4502D6 (CYP2D6) enzyme has been considered a relevant cause of nonresponse to antidepressant drug therapy. Prescribing high doses of antidepressants to such patients leads to high concentrations of potentially toxic metabolites and an increased risk for adverse reactions. Normalization of the metabolic status of ultrarapid metabolizers by inhibition of CYP2D6 activity could offer a clinically acceptable method to successfully treat such patients with antidepressants. METHODS: Five ultrarapid metabolizers with a CYP2D6 gene duplication or triplication were treated with 25 mg nortriptyline twice a day for 3 consecutive weeks, alone during the first week and concomitantly with the CYP2D6 inhibitor paroxetine 10 mg or 20 mg twice a day, respectively, during the second and third weeks. After the third week, nortriptyline was discontinued and the subjects were treated with paroxetine 20 mg twice a day during the fourth study week. At the end of each study week, the steady-state pharmacokinetic parameters of nortriptyline or paroxetine were determined within the dose interval. In addition, the CYP2D6 phenotype was determined by debrisoquin (INN, debrisoquine) test at baseline and at the end of each study phase. Treatment-related adverse events were recorded during drug administration and for 1 week thereafter. RESULTS: All 5 subjects had very low (subtherapeutic) nortriptyline concentrations after 7 days' treatment with nortriptyline only. Addition of paroxetine 10 mg twice a day to the nortriptyline regimen resulted in a change in all individuals to the "normal" extensive debrisoquine metabolizer phenotype, and therapeutic plasma nortriptyline concentrations were achieved in 4 of 5 subjects after a 3 times mean increase in nortriptyline trough concentration (P =.0011). Doubling the paroxetine dose caused a 15 times mean increase in paroxetine trough concentration (P <.001), indicating strong inhibition by paroxetine of its own metabolism. The high paroxetine concentrations in 2 subjects caused them to have the poor debrisoquine metabolizer phenotype and resulted in a further increase in plasma nortriptyline trough concentration (P =.0099). A strong correlation (rank correlation coefficient [r(s)] = 0.89; P <.0001) was observed between paroxetine and nortriptyline trough concentrations. Paroxetine also significantly decreased the fluctuation of nortriptyline concentrations within the dose interval. One subject discontinued the study after the second study week because of adverse effects; otherwise, the study drugs were well tolerated. CONCLUSIONS: Paroxetine, with a daily dosage from 20 to 40 mg, is an effective tool in normalizing the metabolic status of CYP2D6 ultrarapid metabolizers.

Pharmacokinetics of nortriptyline and its 10-hydroxy metabolite in Chinese subjects of different CYP2D6 genotypes.

OBJECTIVES: To study the impact of the CYP2D6*10 allele on the disposition of nortriptyline in Chinese subjects. METHODS: A single dose of 25 mg nortriptyline was given orally to 15 healthy Chinese volunteers who were classified as extensive metabolizers after phenotyping with debrisoquin (INN, debrisoquine) and who were genotyped by allele-specific polymerase chain reaction. Five subjects were homozygous for CYP2D6*1, 5 subjects were homozygous for CYP2D6*10, and 5 subjects were heterozygous for these 2 alleles. Plasma concentrations of nortriptyline and its main metabolite 10-hydroxynortriptyline were measured by liquid chromatography-mass spectrometry, and the pharmacokinetics were studied during 168 hours after the dose. RESULTS: Subjects who were homozygous for CYP2D6*10 had significantly higher total areas under the plasma concentration-time curve (AUC), lower apparent oral clearances, and longer mean plasma half-life of nortriptyline than subjects in the CYP2D6*1/*1 and the heterozygous groups. For 10-hydroxynortriptyline, the AUC was lower and the plasma half-life was longer in subjects who were homozygous for CYP2D6*10 than in subjects in the other 2 groups. CONCLUSION: The CYP2D6*10 allele in Chinese subjects was associated with significantly higher plasma levels of nortriptyline compared with the CYP2D6*1 allele because of an impaired metabolism of nortriptyline to 10-hydroxynortriptyline, particularly in the subjects with the CYP2D6*10/*10 genotype. The results suggest that genotyping of CYP2D6 may be a useful tool in predicting the pharmacokinetics of nortriptyline.

Orally given melatonin may serve as a probe drug for cytochrome P450 1A2 activity in vivo: a pilot study.

BACKGROUND: Melatonin is a hormone that is metabolized by cytochrome P450 (CYP) 1A2 to its main primary metabolite 6-hydroxymelatonin. We therefore evaluated the utility of oral melatonin as a marker of hepatic CYP1A2 activity. METHODS: Twenty-five milligrams of melatonin was given at 9:30 am to 12 healthy Swedish volunteers, who had previously been phenotyped for CYP1A2 with caffeine. Melatonin and conjugated 6-hydroxymelatonin were analyzed by liquid chromatography-mass spectrometry in blood samples taken between 0.5 and 6.5 hours after drug intake. Serum concentrations of melatonin and conjugated 6-hydroxymelatonin, or their ratio at different time points, and the apparent melatonin clearance were tested for correlation with caffeine clearance. RESULTS: We found a significant correlation between apparent clearance of melatonin and caffeine clearance with a Spearman rank correlation coefficient (Rs) of 0.75 (P =.005). The melatonin concentration 1.5 hours after administration also closely correlated with the caffeine clearance (Rs = -0.62; P =.03). Inclusion of conjugated 6-hydroxymelatonin gave no closer correlations. CONCLUSION: Melatonin might be developed as an alternative to caffeine as a probe drug for CYP1A2 phenotyping.

Bantu Tanzanians have a decreased capacity to metabolize omeprazole and mephenytoin in relation to their CYP2C19 genotype.

OBJECTIVE: To investigate the CYP2C19 polymorphism in Tanzanians because this enzyme shows large interindividual differences in activity and metabolizes several drugs of importance in Africa, especially the antimalarial agent chloroguanide (INN, proguanil). METHODS: Two hundred fifty-one Tanzanian healthy volunteers were phenotyped with respect to CYP2C19 with use of a single oral dose of mephenytoin (n = 106), a single oral dose of omeprazole (n = 207), or both. Sixty-two were phenotyped with both probe drugs. The urinary 0- to 8-hour S/R-mephenytoin ratio and the plasma omeprazole metabolic ratio (MR) (omeprazole/hydroxyomeprazole) 3 hours after drug intake were determined. The genotype was determined by analysis for CYP2C19*1 (wt), CYP2C19*2 (m1), and CYP2C19*3 (m2). Ten subjects with high omeprazole MR were screened for new mutations in the CYP2C19 gene by searching for single-strand conformation polymorphisms (SSCP). RESULTS: Eight subjects were classified as mephenytoin poor metabolizers (7.5%). Only 5 of these were homozygous for mutated alleles. The S/R ratio was skewed to the right (lower CYP2C19 activity) compared with other ethnic groups studied previously. No new mutations were found with polymerase chain reaction (PCR)-SSCP. We found 30 volunteers (14.5%) with an MR > 7, which is the antimode found previously in white subjects and Asian subjects. Of the 251 volunteers genotyped, 3.2% were homozygous for mutated alleles and 66.1% were homozygous for the wild-type allele. The allele frequencies of CYP2C19*1, *2, and *3 were 81.5%, 17.9%, and 0.6%, respectively. The correlation between the S/R-mephenytoin ratio and the omeprazole MR was significant (Spearman r = 0.59; P < .01). CONCLUSION: Tanzanians have a decreased capacity to metabolize both omeprazole and mephenytoin when their genotype is compared with metabolic capacity and genotype in other previously studied populations. We identified a low frequency of the Asian allele (CYP2C19*3). Although we did not find any new mutations, our results may be consistent with the presence of yet-unidentified mutations of CYP2C19 that causes decreased CYP2C19 activity in the Tanzanian population.

Carbamazepine therapy in trigeminal neuralgia: clinical effects in relation to plasma concentration.

Seven patients with trigeminal neuralgia were treated with carbamazepine at three dose levels, each period lasting for six days. A single-blind technique was used, the patients being unaware of the dose changes. During the last three days of each dose treatment, the pain score was determined by the patients and the plasma concentrations of carbamazepine and its epoxide metabolite were measured. There was a correlation between the dose and plasma level of carbamazepine (r = .56; P < .01). At the carbamazepine doses studied (200 to 1,400 mg/day), no indication of saturation kinetics was seen. As the ratio between the plasma levels of the epoxide and carbamazepine was relatively low and constant, it was not possible to evaluate the potency of the epoxide. In six of the patients studied a plasma level-effect relationship was found. The best effect was seen at carbamazepine levels between 24 and 43 mu mole/L (5.7 and 10.1 microgram/mL). In one patient who was studied twice, the plasma level-response curve was different on the two occasions. Side effects were recorded in two patients, both with carbamazepine plasma levels above 33 mu mole/L (7.9 microgram/mL).

Carbamazepine metabolism in man. Induction and pharmacogenetic aspects.

The metabolism of carbamazepine (CBZ) was studied in 3 groups of subjects: (1) 6 healthy volunteers given a single dose of 200mg carbamazepine; (2) 4 epileptic patients on carbamazepine monotherapy; and (3) 5 patients receiving carbamazepine in combination with other anticonvulsants. Carbamazepine kinetics in the patients were investigated by use of 15N-CBZ. The mean plasma clearances of carbamazepine were 19.8, 54.6 and 113.3 ml/h/kg in groups 1, 2 and 3, respectively. The increased clearance in the patients was mainly due to an induction of the epoxide-diol pathway, as reflected by an increased urinary excretion of the trans-CBZ-diol metabolite. The urinary excretion (as a percentage of the administered dose) of 9-hydroxymethyl-10-carbamoyl-acridan (9-OH-CBZ) was also increased, whereas the excretion of 2-OH-CBZ and 3-OH-CBZ in groups 2 and 3 were decreased in comparison with group 1. As it has been suggested that 9-OH-CBZ is formed from carbamazepine-10,11-epoxide (CBZ-E) or trans-CBZ-diol, the formation of 9-OH-CBZ was investigated in 3 patients with trigeminal neuralgia treated with carbamazepine or CBZ-E as monotherapy on separate occasions. The urinary excretion of 9-OH-CBZ was 1.9, 3.3 and 4.0% of the trans-CBZ-diol excretion during CBZ-E therapy and 23, 32 and 24%, respectively, during carbamazepine administration. Thus only a minor part of the 9-OH-CBZ excreted in urine during carbamazepine therapy is formed via the epoxide-diol pathway. Data on plasma concentrations of carbamazepine and CBZ-E, and on urinary excretion of trans-CBZ-diol from 4 patients on carbamazepine therapy were used to calculate the plasma clearance of CBZ-E. The hydration of CBZ-E during carbamazepine therapy was found to be induced, but to a lesser extent than the epoxidation of carbamazepine. The interrelationship between carbamazepine-epoxidation and oxidative metabolic reactions of some other drugs was also studied in 8 healthy volunteers. Carbamazepine-epoxidation was not correlated to 4-hydroxylation of debrisoquine, oxidation of sparteine, 3- and 4-hydroxylation and demethylation of antipyrine, demethylation of amitriptyline, or total metabolism of theophylline.