Maternal perinatal diet induces developmental programming of bone architecture.

Maternal high-fat (HF) diet can alter offspring metabolism via perinatal developmental programming. This study tests the hypothesis that maternal HF diet also induces perinatal programming of offspring bone mass and strength. We compared skeletal acquisition in pups from C57Bl/6J mice fed HF or normal diet from preconception through lactation. Three-week-old male and female pups from HF (HF-N) and normal mothers (N-N) were weaned onto normal diet. Outcomes at 14 and 26 weeks of age included body mass, body composition, whole-body bone mineral content (WBBMC) via peripheral dual-energy X-ray absorptiometry, femoral cortical and trabecular architecture via microcomputed tomography, and glucose tolerance. Female HF-N had normal body mass and glucose tolerance, with lower body fat (%) but higher serum leptin at 14 weeks vs. N-N (P<0.05 for both). WBBMC was 12% lower at 14 weeks and 5% lower at 26 weeks, but trabecular bone volume fraction was 20% higher at 14 weeks in female HF-N vs. N-N (P<0.05 for all). Male HF-N had normal body mass and mildly impaired glucose tolerance, with lower body fat (%) at 14 weeks and lower serum leptin at 26 weeks vs. N-N (P<0.05 for both). Serum insulin was higher at 14 weeks and lower at 26 weeks in HF-N vs. N-N (P<0.05). Trabecular BV/TV was 34% higher and cortical bone area was 6% higher at 14 weeks vs. N-N (P<0.05 for both). These data suggest that maternal HF diet has complex effects on offspring bone, supporting the hypothesis that maternal diet alters postnatal skeletal homeostasis.

Comparative in vitro and in vivo study of a sugar-coated chloroquine preparation marketed in Tanzania versus an ordinary brand.

OBJECTIVE: To investigate the absorption and the quality of a sugar-coated chloroquine (CQ) marketed in Tanzania. METHOD: Twenty healthy volunteers were randomised to take either the test brand (group A) or a control chloroquine phosphate (group B). Each subject received 300 mg chloroquine base. Whole blood dried on filter papers were collected at time 0 and at 15 and 30 min and at 1, 2, 3, 4, 6, 8, 24, 36, 48, 72 and 168 h after drug intake. Urine samples were collected at time 0, 0-4 h, 4-8 h, 8-24 h, 24-48 h and 48-72 h after drug administration. In an in vitro study, six tablets from each of the two CQ preparations were checked for the amount of active drug contained in each tablet and their dissolution rates. RESULTS: The blood concentration Area Under the Curve (AUC) of group B was about 10% larger than that of group A. The total amounts of CQ plus deethylchloroquine excreted with the urine during the 72-h study period were 5% for group A and 6% for group B. None of the pharmacokinetic parameters were significantly different between the two groups. All the tablets contained the labelled amount of chloroquine; however, one tablet from the test drug failed to fulfil the required dissolution rate. CONCLUSION: We found no major difference between the AUCs of the two CQ preparations, but the sugar-coated brand has shown to have variable dissolution rate.

Slow chloroguanide metabolism in Tanzanians compared with white subjects and Asian subjects confirms a decreased CYP2C19 activity in relation to genotype.

BACKGROUND: We have previously found decreased CYP2C19 activity in Tanzanians tested with mephenytoin and omeprazole in relation to genotype when compared with white and Asian subjects. OBJECTIVE: We investigated the impact of CYP2C19 genotype and phenotype on chloroguanide (INN, proguanil) metabolism to its metabolites cycloguanil and 4-chlorophenylbiguanide. METHODS: A single oral chloroguanide dose was given to 25 healthy Tanzanian subjects with CYP2C19 genotypes (CYP2C19*1, CYP2C19*2, and CYP2C19*3). Homozygous wild-type and mutated genotype groups were chosen randomly, but the heterozygous genotype group was chosen with a range in phenotype. We used a novel HPLC method for drug determination. RESULTS: Pharmacokinetics of chloroguanide did not differ between groups. Maximum plasma concentration (Cmax) and area under the plasma concentration versus time [AUC(0-infinity)] for cycloguanil was significantly lower (t test P < .05) in the homozygously mutated group compared with the homozygously wild-type group. There were similar significant group differences of median urinary excretion. The chloroguanide/cycloguanil ratio closely correlated (r(s) = .87) with omeprazole metabolic ratio, confirming that Tanzanian subjects are generally slower CYP2C19 metabolizers. It also confirms that CYP2C19 genotype and phenotype predicts cycloguanil formation. In addition, a 3-hour plasma sample metabolic ratio also seems to be a proper time for omeprazole phenotyping in Tanzanian subjects. Because the plasma concentrations of cycloguanil and 4-chlorophenylbiguanide covary (r(s) = .89), it is now suggested that their formation be catalyzed by the same enzyme (ie, CYP2C19) through a common intermediate, the structure of which is also presented. CONCLUSIONS: As shown in an earlier study, also with a third substrate, Tanzanians have a lower capacity to form cycloguanil than white and Asian subjects. Individuals with two mutated alleles have lower metabolic capacity than individuals with two wild-type alleles or individuals in the heterozygous group, which may lead to chloroguanide therapeutic failure. This knowledge should be important when selecting appropriate patients and doses of chloroguanide in different populations.

Evaluation of caffeine as an in vivo probe for CYP1A2 using measurements in plasma, saliva, and urine.

Twenty-five healthy volunteers were given 100 mg caffeine orally and several estimates of cytochrome P450 1A2 (CYP1A2) activity were evaluated. The validation was performed by correlation of different parameters in plasma, saliva, and urine to two measures of caffeine clearance, CL(oral) and CL(137X-->17X) that served as standards of reference. Two subjects were excluded because of noncompliance with a caffeine-free diet. In the remaining 23 subjects, both plasma and saliva total clearances of caffeine were highly correlated with each other (r(s) = 0.97, p < 0.0001). The ratio 17X/137X restricted to one sampling point taken 4 hours after dose, showed a high correlation (r(s)) with CL(oral) and CL(137X-->17X) in plasma (0.84/0.83) and saliva (0.82/0.77) (p < 0.0001 for all the correlation values) where 17X is 1,7-dimethylxanthine (paraxanthine) and 137X is 1,3,7-trimethylxanthine (caffeine). Additionally, the ratio (AFMU + 1U + 1X + 17U + 17X)/137X in a 0-24 hours urine sampling showed the highest correlation with CL(137X-->17X) (r(s) = 0.85, p < 0.001) where AFMU is 5-acetylamino-6-formylamino-3-methyluracil, 1U is 1-methyluracil, 1X is 1-methylxanthine, and 17U is 1,7-dimethyluric acid. The major estimates of CYP1A2 activity were significantly less in nonsmoking females, and this probably was related to the use of oral contraceptives in this subpopulation. In summary, among caffeine-based approaches for CYP1A2, the authors recommend either plasma or saliva 17X/137X ratio and the urinary (AFMU + 1U + 1X + 17U + 17X)/137X ratio during a sampling interval of at least 8 hours, starting at time zero since caffeine intake. These indices are simple, reliable, and relatively inexpensive estimates of CYP1A2 activity to be used in the study of human populations.

[Intensified insulin treatment is cost-effective]. / Intensifierad insulinbehandling bär sina egna merkostnader.

Both the Diabetes Control and Complications Trial (DCCT) in USA/Canada, and Stockholm Diabetes Intervention Study (SDIS) showed intensified insulin treatment and reduced glycaemia to prevent complications in patients with insulin-dependent (type I) diabetes mellitus. In the DCCT, the intensified treatment was considered cost-effective. In the SDIS, investigation of the direct increase in costs due to the intensified insulin treatment showed the saving in direct costs due to the reduction in photocoagulation requirements, and in the prevalence of renal insufficiency and of amputation, to correspond to 10 years' intensive insulin treatment. Thus, as intensified insulin treatment in type I diabetes reduces direct suffering at a low cost, it may be regarded as 'evidence-based' and mandatory.

Decreased capacity for debrisoquine metabolism among black Tanzanians: analyses of the CYP2D6 genotype and phenotype.

The cytochrome P450 2D6 (CYP2D6) genotypes and phenotypes of 106 unrelated, healthy black Tanzanians of Bantu origin were investigated. The results revealed a population with a generally decreased capacity to metabolize the CYP2D6 substrate debrisoquine with 59% of the Tanzanian extensive metabolisers having debrisoquine metabolic ratios (MRs) > 1 versus 20% in Caucasians. This decrease in metabolic capacity was not fully explained by the partially or fully detrimental CYP2D6 gene mutations analysed for in this study. As many as 7% poor metabolizers of debrisoquine were identified but none was homozygous for defective CYP2D6 alleles. The majority among the group of poor metabolizers had relatively low metabolic ratios. The mutational profile indicated a closer association of the Tanzanian CYP2D locus to that of Zimbabweans rather than to that of Ethiopians. The defective alleles CYP2D6*3, *4, *5 and *6 were found at low frequencies (0%, 1%, 6%, 0%, respectively), whereas the CYP2D6*17 allele causing an enzyme with altered specificity was common (allele frequency = 17%). It is concluded that the CYP2D6 genotype in the Tanzanian Bantu population is different from that of other African populations examined to date and that further studies are required to explain the generally lower capacity to metabolize CYP2D6 substrates.

Metabolism of ropivacaine in humans is mediated by CYP1A2 and to a minor extent by CYP3A4: an interaction study with fluvoxamine and ketoconazole as in vivo inhibitors.

BACKGROUND: Potential drug-drug interactions can be identified in vitro by exploring the importance of specific cytochrome P450 (CYP) isozymes for drug metabolism. The metabolism of the local anesthetic ropivacaine to 3-hydroxyropivacaine and (S)-2',6'-pipecoloxylidide was shown in vitro to be dependent on CYP1A2 and 3A4, respectively. In this in vivo model study we quantitated the role of these 2 isozymes for the metabolism of ropivacaine. METHODS: In a randomized, 3-way crossover study, 12 healthy subjects received a single dose of 40 mg ropivacaine intravenously alone or combined either with 25 mg fluvoxamine as a CYP1A2 inhibitor or with 100 mg ketoconazole as a CYP3A4 inhibitor twice daily for 2 days. Venous plasma and urine samples were collected over 10 hours and 24 hours, respectively. The samples were analyzed for ropivacaine base, 3-hydroxyropivacaine, and (S)-2',6'-pipecoloxylidide. RESULTS: Coadministration with fluvoxamine decreased the mean total plasma clearance of ropivacaine from 354 to 112 mL/min (68%), whereas ketoconazole decreased plasma clearance to 302 mL/min (15%). The relative changes in unbound plasma clearance were similar to the changes in total plasma clearance. The ropivacaine half-life (t1/2) of 1.9 hours was almost doubled during fluvoxamine administration and the plasma concentration at the end of infusion increased slightly, whereas the corresponding parameters after ketoconazole administration remained unchanged. Coadministration with ketoconazole almost abolished the (S)-2',6'-pipecoloxylidide concentrations in plasma, whereas fluvoxamine administration increased the (S)-2',6'-pipecoloxylidide levels. The fraction of dose excreted as 3-hydroxyropivacaine in urine decreased during fluvoxamine administration from 39% to 13%. CONCLUSIONS: CYP1A2 is the most important isozyme for the metabolism of ropivacaine. Drug-drug interactions with strong inhibitors of this isozyme could be of clinical relevance during repeated administration. A potent inhibitor of CYP3A4 causes a minor decrease in clearance, which should be of no clinical relevance.

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.

Quantification of the O- and N-demethylated and the glucuronidated metabolites of codeine relative to the debrisoquine metabolic ratio in urine in ultrarapid, rapid, and poor debrisoquine hydroxylators.

The O-demethylation of codeine is polymorphic and catalyzed by CYP2D6. The metabolites of codeine formed through O- and N-demethylation as well as glucuronidation were quantified in the ultrarapid metabolizers of debrisoquine and compared with the normal extensive (EM) and poor metabolizers (PM). The urinary codeine and its seven metabolites were detected after 25 mg codeine in 24 healthy Caucasian subjects with low debrisoquine metabolic ratios (MR, < or = 0.11) and a group of 132 subjects tested earlier with codeine and debrisoquine including 114 EMs (MR < 12.6) and 18 PMs (MR > 12.6). Whereas the O-demethylated metabolites accounted for < 0.4% of the total recovery on average in the PMs and 1.7% to 8.7% in the EMs, they accounted for 15.3% in the 24 subjects with ultrarapid metabolism of debrisoquine. This study suggests that the ultrarapid debrisoquine hydroxylators may develop increased O-demethylated metabolite-dependent effects or side-effects of codeine.

Intraindividual and interindividual variability in the disposition of the local anesthetic ropivacaine in healthy subjects.

To predict the risk of adverse reactions to local anaesthetics used in clinical practice, it is crucial to know whether any nonlinearity exists in their pharmacokinetics. The disposition of ropivacaine, a new local anesthetic agent, was evaluated in healthy subjects on the basis of plasma levels in the concentration range obtained after regional anaesthesia. Three intravenous doses of ropivacaine hydrochloride (20, 40, and 80 mg) were given in a double-blind, randomized, complete crossover design. Analysis of variance was used to assess the importance of intra- versus interindividual variability in the basic pharmacokinetics. The mean plasma clearance (400 ml/min), volume of distribution at steady state (40 l), and terminal half-life (1.7 h) were similar, irrespective of dose. The intersubject variability for these parameters was higher than the intrasubject variability. A slight increase in free fraction (15%) with increasing dose might indicate that the lower limit for saturation of protein binding may be reached at the higher plasma levels. One subject (80 mg) reported numbness of the lower lip 2 min after the end of the infusion, which may be a sign of systemic CNS toxicity. The total and free plasma concentration was extrapolated to 1.7 and 0.08 mg/l, respectively.

Intragastric pH after oral administration of single doses of ranitidine effervescent tablets, omeprazole capsules and famotidine fast-dissolving tablets to fasting healthy volunteers.

BACKGROUND: The therapeutic effect of drugs inhibiting acid production on acid-related discomforts is related to both the onset and duration of action of the drug. The effects on gastric pH by single oral doses of some acid-inhibiting drugs were investigated by measuring daytime (morning to lunch) intragastric pH in healthy volunteers. METHODS: This randomized, single-dose, 4-way crossover study included 15 healthy fasting subjects. Effervescent ranitidine tablets 150 and 300 mg, fast-dissolving famotidine tablets 20 mg and capsules of omeprazole 20 mg were administered. Measurements of intragastric pH were performed every 4 s for 10 min prior to drug administration and during the following 4 h. RESULTS: The effervescent ranitidine tablets (150 or 300 mg) produced similar changes in intragastric pH: following an immediate increase to about pH 5, intragastric pH decreased slightly over the next 10-20 min. Thereafter pH increased steadily, reaching pH 4 after 20-40 min and pH 6 after about 70 min. After famotidine, pH 4 was reached after 80 min, significantly slower than ranitidine. After omeprazole, pH 3 was never reached. Ranitidine 150 and 300 mg showed significantly larger integrated pH responses over the 4-h observation period, compared to famotidine (P = 0.0288 and 0.0074) or omeprazole (P < 0.001). CONCLUSIONS: After single-dose administration to healthy fasting volunteers), ranitidine effervescent tablets showed a significantly more rapid onset of action and a significantly larger integrated pH response compared to either famotidine 20 mg fast-dissolving tablets or omeprazole 20 mg capsules.

Systemic absorption and block after epidural injection of ropivacaine in healthy volunteers.

BACKGROUND: For local anesthetics, the process of removal from the site of administration influences the duration of anesthesia and the risk for systemic toxicity to develop. The systemic absorption of epidural ropivacaine and the time profile of sensory and motor block were studied in healthy volunteers. METHODS: Nine persons simultaneously received 150 mg ropivacaine hydrochloride (7.5 mg/ml) epidurally and 40 mg deuterium-labeled (2H3)ropivacaine hydrochloride (0.25 mg/ml) intravenously. Peripheral arterial and venous plasma samples were collected, and assessments of sensory and motor block were made. RESULTS: The arterial plasma concentrations increased faster than the venous concentrations, with 50% higher maximum concentrations after both intravenous and epidural administration. The absorption was biphasic. A correlation was seen between the duration of sensory block and the slower absorption half-life; that is, the longer the half-life, the longer the duration. The extent of spread varied among the volunteers, with the median upper block level not exceeding T12. The motor block (Bromage score 1) was of slower onset (median, 0.4 h) and of shorter duration (median, 4.1 h) than the sensory block (onset, 0.2 h; duration, 6.5 h at L2 medians). CONCLUSIONS: As much as 50% differences were seen in the arteriovenous plasma concentrations of ropivacaine during the first hour, which has implications for the interpretation of systemic toxic plasma concentrations. The absorption into the general circulation was biphasic, with a correlation between the sensory block and the slower absorption half-life. A faster onset and a longer duration of sensory compared with motor block was seen.

Involvement of CYP2D6 but not CYP2C19 in nicergoline metabolism in humans.

1. Nicergoline, an ergot derivative previously used as a vasodilator, has gained a new indication in treating the symptoms of senile dementia. 2. Nicergoline is rapidly hydrolysed to an alcohol derivative, 1-methyl-10-alpha-methoxy-9,10-dihydrolysergol (MMDL), which is further N-demethylated to form 10-alpha-methoxy-9,10-dihydrolysergol (MDL). A few individuals display aberrant metabolism of this drug, as shown by their diminished capacity to form the MDL metabolite. The aim of this study was to determine whether defective nicergoline metabolism is associated with the debrisoquine and/or the S-mephenytoin hydroxylation polymorphisms. 3. After a single, oral 30 mg dose of nicergoline, the plasma concentrations of its two metabolites were studied in 15 subjects, divided into three groups with respect to their debrisoquine and S-mephenytoin hydroxylation phenotypes. 4. The pharmacokinetic parameters of MMDL and MDL were similar in the ten subjects who were extensive metabolisers of debrisoquine (five of whom were poor metabolisers of S-mephenytoin) (mean MMDL Cmax 59 nmol l-1 and AUC (0, th) 144 nmol l-1h, mean MDL Cmax 183 nmol l-1 and AUC 2627 nmol l-1h) but were markedly different from the five subjects who were poor metabolisers of debrisoquine (mean MMDL Cmax 356 nmol l-1 and AUC 10512 nmol l-1h, MDL concentrations below limit of quantitation). 5. We conclude that the formation of MDL from MMDL in the metabolism of nicergoline is catalysed to a major extent by CYP2D6 and that the observed interindividual variation in the metabolic pattern of the drug is related to the debrisoquine hydroxylation polymorphism.

Disposition of fluvoxamine in humans is determined by the polymorphic CYP2D6 and also by the CYP1A2 activity.

BACKGROUND: Fluvoxamine is a selective serotonin reuptake inhibitor used widely in the treatment of depression and other psychiatric diseases, but little is known about the specific isozymes involved in its metabolism. This study investigated the relationship between fluvoxamine disposition and the polymorphic CYP2D6 and the polycyclic aromatic hydrocarbon (as contained in cigarette smoke) inducible CYP1A2. METHODS: Fluvoxamine (50 mg orally) was given to 10 extensive metabolizers and four poor metabolizers of debrisoquin, and concentrations were assessed in plasma by high performance liquid chromatography. Five of the extensive metabolizers and one of the poor metabolizers were smokers of more than 10 cigarettes per day. The CYP1A2 activity was determined by means of a urinary caffeine test. RESULTS: Compared with nonsmoking extensive metabolizers, nonsmoking poor metabolizers had a statistically significant (p = 0.02, Mann-Whitney U test) about twofold higher maximum plasma concentration, longer half-life, and fivefold lower oral clearance of fluvoxamine. The oral clearance of fluvoxamine correlated to the CYP1A2 index in the 14 subjects (rs = 0.58; p < 0.05; Spearman rank correlation). CONCLUSION: The disposition of fluvoxamine in humans is associated with the polymorphic CYP2D6 activity, but CYP1A2 also seems to be involved.

Monitoring free extracellular valproic acid by microdialysis in epileptic patients.

This report describes the first experiences with monitoring of valproic acid pharmacokinetics in patients with epilepsy by subcutaneous microdialysis. We could demonstrate good correspondence between total concentration in plasma and free concentration in plasma and dialysate. In this study the dialysate concentrations were not corrected for in vivo recovery because the aim was to explore the possibilities of the method in routine clinical work rather than to estimate absolute concentrations in extracellular fluid. In one patient, microdialysis was continued for 3 days without problems. The dialysis probe with a small portable pump could be carried without any notable interference with daily activities of patients in the ward. No side effects were noted. The results encourage further studies along two lines: to investigate the free-concentration effect relation for valproic acid and to monitor drug concentration under nonhospital conditions in order to study the interaction between daily activities and drug concentration.

[Need for a long-term program in the follow-up of anti-lipid treatment following coronary artery surgery?]. / Behövs långsiktiga program för uppföljning av blodfettsbehandling efter kranskärlskirurgi?

The positive effects of cholesterol-lowering therapy in coronary artery disease are well recognised. This study, on 99 consecutive coronary artery bypass grafted patients, shows that an intensive one-year follow-up at a secondary prevention specialist clinic significantly improves cholesterol levels compared to conventional follow-up in the primary health care system. However, these positive results are not consistent after a 2.6 year return to the primary health care. Consequently, improved collaboration between hospital and primary health care physicians in the development of structured secondary prevention programmes is essential.

Clozapine disposition covaries with CYP1A2 activity determined by a caffeine test.

In a previous study we showed that the disposition of clozapine after a single oral dose is unrelated to either debrisoquine or S-mephenytoin hydroxylation polymorphism. The same 14 healthy subjects studied in that investigation were given 150 mg of caffeine. The reciprocal of plasma clozapine AUC (0,24), was correlated with an index of the N3-demethylation of caffeine (rs = 0.84; P = 0.0024), used as a measure of cytochrome P4501A2 (CYP1A2) activity. N1- and N7-demethylation indices of caffeine also reflect CYP1A2 activity and were also correlated with clozapine clearance (rs = 0.89 and 0.85; P = 0.0013 and 0.0023; respectively). No significant relationships with xanthine oxidase and N-acetyl transferase activity, also assessed by a caffeine test, were found. This study suggests that clozapine is metabolised by CYP1A2 to a major extent.

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.