Extensive Metabolizers Of Sparteine Research Articles

CYP2D6 extensive, intermediate, and poor phenotypes and genotypes in a Polish population

This study investigated the distribution of the CYP2D6 genotypes and phenotypes in a Polish population and compared the concordance of the two methods. Six hundred unrelated healthy individuals from southwestern Poland were studied. The CYP2D6 phenotype was analyzed in 300 individuals using sparteine as a model drug. The CYP2D6 genotype was analyzed in 300 individuals by polymerase chain reaction amplification and restriction fragment length polymorphism techniques for the CYP2D6*1, CYP2D6*3, and CYP2D6*4 alleles. Additionally, in 60 randomly selected healthy individuals both the CYP2D6 phenotype and genotype was assessed to determine accordance between the methods. Of 300 participants in the study 25 (8.3%) were classified as poor metabolizers, 44 (14.7%) as intermediate metabolizers, and 231 (77%) as extensive metabolizers of sparteine. The frequency of CYP2D6*1, CYP2D6*3, and CYP2D6*4 alleles among the genotyped 300 persons was 75.7%, 1.3%, and 23.0%, respectively. The frequency of CYP2D6 deficient genotypes in a Polish population (8.0%) was similar to phenotyping results. The comparison of phenotype and genotype in 60 randomly selected individuals showed a good concordance of the obtained results. CONCLUSIONS. The frequencies of poor metabolizers for CYP2D6 phenotype (8.3%) and genotype (8.0%) in a Polish population from the southwestern region are in concordance and compare well with most results of poor oxidation metabolizers in other white populations.

Codeine in post-operative pain. Study of the influence of sparteine phenotype and serum concentrations of morphine and morphine-6-glucuronide.

Within the past decade, human experimental pain studies have supported the 50-year-old hypothesis that codeine is a prodrug, which has to be converted to morphine to exert an analgesic effect. This study aimed at evaluating the impact of sparteine phenotype and serum concentrations of morphine on the efficacy of codeine in post-operative pain. Eighty-one patients with a pain rating of 3 or more on a 0-10 numerical rating scale 0.5 h after surgery were included in the study. The patients were given an oral dose of 100 mg codeine and rated pain with the numerical rating scale 0.5 h and 1 h after medication. Blood for determination of serum concentration of codeine and its metabolites was collected 1 h after medication, and a 12-h urine sample after administration of 100 mg sparteine was used to determine the sparteine phenotype. Eight patients were poor metabolizers and 66 were extensive metabolizers of sparteine, while the urine samples for the remaining seven patients were lost. In 22 patients, including the eight poor metabolizers, the serum concentrations of both morphine and morphine-6-glucuronide (M6G) were below the limit of determination of the assay, i.e. 1.5 nmol x l(-1) and 2 nmol x l(-1), respectively. A sum of the concentration of these two substances below 10 nmol x l(-1) was found in an additional eight patients. The sum of differences between pre- and post-operative pain ratings did not differ between the two phenotypes (P = 0.60), whereas the 30 patients with serum concentrations of morphine plus M6G below 10 nmol x l(-1) had a marginally significant lower sum than the 51 patients with higher levels of these substances (median 1.5 vs 2.5, P = 0.058). A low serum concentration of morphine and M6G seems to be common in patients treated with codeine for post-operative pain, and low concentrations of these active substances may be related to decreased efficacy of codeine.

Evaluation of genetically determined sparteine oxidation and sulfadimidine acetylation polymorphism in women with breast cancer

Abstract The relationship between genetically determined polymorphic oxidation and acetylation and susceptibility to neoplastic diseases has aroused much interest. The aim of our study was to evaluate whether women with breast cancer differ from healthy women in their ability to oxidize sparteine and acetylate sulfadimidine as model drugs. The results of our study revealed a predominance of the percentage of extensive metabolizers (EMs) of sparteine (97.8%) among 90 women with breast cancer in comparison to the percentage of EM (93.2%) in 74 healthy women. Among very extensive metabolizers of sparteine (VEM), with metabolic ratio (MR)

Imipramine metabolism in relation to the sparteine oxidation polymorphism--a family study.

The relationship between genetic polymorphism and imipramine metabolism has never been studied in a family study. A sparteine/mephenytoin test was carried out in 31 parents and 20 siblings of 18 Danish poor metabolizers of sparteine (PMs). One week later, each subject took 25 mg imipramine followed by urine collection for 24 h. The urinary content of imipramine, desipramine, 2-hydroxy-imipramine and 2-hydroxy-desipramine was assayed by HPLC. There were 10 PMs (20%; 9.8-33%, 95% confidence interval) and 41 extensive metabolizers of sparteine (EMs) among parents and siblings. In 26 of the 28 PMs among probands and relatives, there were concordance between phenotype and genotype: D6-A/D6-D (n = 2), D6-A/D6-B (n = 5), D6-B/(n = 15) or D6-B/D6-D (n = 4). Two PMs were apparently heterozygous (EMs), D6-wt/D6-B. Accordingly, based on the present sample of 28 PMs the specificity of the genotype test was 100% and the sensitivity was 92.9%. Two EMs were homozygous dominant D6-wt/and 39 were heterozygous EMs; D6-wt/D6-D (n = 5), D6-wt/D6-B (n = 27), D6-wt/D6-A (n = 6), D6-wt/D6-wt* (unknown mutation) (n = 1). As previously reported in a population study the hydroxylation ratios (i.e. 2-hydroxymetabolite over parent compound) of imipramine were much lower in PMs than in EMs. This and the pedigrees confirmed the co-segregation of sparteine oxidation, imipramine 2-hydroxylation and the CYP2D6 genotype. None of the hydroxylation ratios could separate EMs and PMs completely, mainly because the 2-hydroxylation of imipramine also depends on P450s other than CYP2D6.

Assessment of individual CYP2D6 activity in extensive metabolizers with renal failure: Comparison of sparteine and dextromethorphan*

To examine whether the variability of CYP2D6 activity in patients with chronic renal failure can be assessed, particularly among subjects with the extensive metabolizer phenotype, by use of standard in vivo indexes of CYP2D6 activity derived from oral administration of dextromethorphan and sparteine. A single 100 mg oral dose of sparteine and a single 40 mg oral dose of dextromethorphan were administered on two occasions to 12 patients with chronic renal failure (creatinine clearance ranging from 20 to 70 ml/min) and 12 age- and sex-matched healthy subjects. Sparteine clearances, sparteine metabolic ratio, and urinary recovery of dextrorphan were calculated. Patients and healthy control subjects were not selected on the basis of their CYP2D6 phenotypes. Chronic renal failure was associated with a decrease in sparteine partial metabolic clearance to dehydrosparteine (median of 322 ml/min and range of 62 to 670 ml/min in patients with renal failure versus median of 635 ml/min and range of 77 to 1276 ml/min in normal subjects; p < 0.02). Sparteine apparent oral clearance (p < 0.03) and renal clearance (p < 0.001) decreased in patients with renal failure. However, sparteine metabolic ratio was not significantly altered in patients with renal failure and showed that all patients were extensive metabolizers of sparteine. Although fractional urinary excretion of dextrorphan decreased in patients with renal failure (median, 24.4%; range, 9.7% to 55.9%) compared with control (median, 47.5%; range, 24.1% to 72.1%) (p = 0.02), it also showed that all subjects were extensive metabolizers of dextromethorphan. The amount of dextromethorphan excreted in urine correlated with creatinine clearance independently from CYP2D6 activity measured as sparteine partial metabolic clearance. However, it did not correlate with sparteine metabolic ratio or with fractional urinary excretion of dehydrosparteine. Assessment of CYP2D6 activity by use of dextromethorphan and sparteine is possible in extensive metabolizer patients with chronic renal failure. However, in these subjects, dextromethorphan and sparteine do not reflect CYP2D6 activity in the same way.

Moclobemide, a substrate of CYP2C19 and an inhibitor of CYP2C19, CYP2D6, and CYP1A2: a panel study.

The reversible monoamine oxidase A inhibitor moclobemide was given in single (300 mg) and multiple doses (600 mg/day) to 11 male and four female healthy volunteers (age range, 23 to 27) who were either poor metabolizers of S-mephenytoin (n = 7) or extensive metabolizers of S-mephenytoin (n = 8). All were extensive metabolizers of sparteine. Poor metabolizers of S-mephenytoin had lower moclobemide clearance values (median, single dose: 16.1 versus 43.2 L.hr-1; steady state: 13.4 versus 22.1 L.hr-1) and longer moclobemide half-life values (median, single dose: 4.0 versus 1.8 hours; steady state: 5.1 versus 2.7 hours) than extensive metabolizers of S-mephenytoin. The plasma levels of a metabolite formed by C-hydroxylation (Ro 12-8095) were lower in poor metabolizers of S-mephenytoin than in extensive metabolizers of S-mephenytoin. Moclobemide thus partially undergoes oxidative metabolism by way of the polymorphic CYP2C19. A combined mephenytoin, sparteine, and caffeine test performed before, during, and after multiple dosing of moclobemide showed changes in the metabolic indexes compatible with a reversible inhibition of oxidation by way of the corresponding CYP enzymes--CYP2C19, CYP2D6, and CYP1A2--during moclobemide treatment.

Proguanil metabolism is determined by the mephenytoin oxidation polymorphism in Vietnamese living in Denmark.

1. A sparteine/mephenytoin phenotyping test was carried out in 37 Vietnamese living in Denmark. By visual inspection the urinary S/R-mephenytoin ratio appeared to show a bimodal frequency distribution. Eight putative poor metabolizers of mephenytoin, PMm (22%), had S/R-mephenytoin ratios from 0.79 to 1.12 and 29 putative extensive metabolizers of mephenytoin, EMm, had S/R-mephenytoin ratios < or = 0.55. All of the subjects were extensive metabolizers of sparteine with urinary metabolic ratios from 0.15 to 2.4. 2. The metabolism of the antimalarial prodrug proguanil was studied in 34 of the subjects after a single oral dose of 100 mg. The median 12 h urinary recoveries of the active metabolite cycloguanil and the minor metabolite 4-chlorphenylbiguanide were 5.8 and 1.9% of the dose, respectively, in 26 EMm compared with 1.6 and 0.4%, respectively, in 8 PMm (P < 0.001, Mann-Whitney U-test). 3. There was no statistically significant correlation (Spearmans rs) between any index of proguanil metabolism and the sparteine metabolic ratio.

Citalopram

The pharmacokinetic interactions between the selective serotonin reuptake inhibitor citalopram, given as an oral dose of 40 mg/day for 10 days, and (1) levomepromazine (50 mg single oral dose), (2) imipramine (100 mg single oral dose), and (3) lithium (30 mmol/day orally for 5 days) were examined in three panels each of 8 healthy young male volunteers (age 20-31). All volunteers were classified as extensive metabolizers of sparteine and mephenytoin. Each subject completed three study phases--one with citalopram alone, one with one of the three other drugs, alone, and one with citalopram combined with the corresponding other drug. For citalopram and its metabolites, a non-enantioselective analytical method (high-performance liquid chromatography) was used. Only two statistically significant interactions were indicated. First, levomepromazine caused a 10-20% increase from the initial steady-state levels of the primary citalopram metabolite, desmethylcitalopram. Second, citalopram caused approximately 50% increase in the single-dose area under the serum concentration/time curve of desipramine (primary metabolite or imipramine) and a corresponding reduction in the level of the subsequently formed metabolite 2-hydroxydesipramine. These findings are in agreement with the recent observations that (1) the demethylation of desmethylcitalopram (to didesmethylcytalopram) is partly mediated via the sparteine/debrisoquine oxygenase (CYP2D6) and that levomepromazine is a potent inhibitor of CYP2D6, and (2) that desmethylcitalopram has a somewhat stronger affinity for CYP2D6 than desipramine, and therefore may inhibit the hydroxylation of desipramine, which is also a substrate of CYP2D6.

Drug metabolism and genetic polymorphism in subjects with previous halothane hepatitis.

To test the hypothesis that halothane hepatitis is caused by a combination of altered drug metabolism and an immunoallergic disposition, the metabolism of antipyrine, metronidazole, sparteine, phenytoin, and racemic R- and S-mephenytoin was investigated in seven subjects with previous halothane hepatitis. The HLA tissue types and the complement C3 phenotypes were also determined. The metabolism of antipyrine and metronidazole was within normal range in all subjects, and they were all fast or extensive metabolizers of sparteine, mephenytoin, and phenytoin. HLA tissue types were unremarkable. Five of the seven subjects had complement C3 phenotypes F or FS. In the general population phenotype S is the most common, but the difference in complement C3 phenotypes is not statistically significant (p = 0.07). We conclude, although in a limited number of patients, that subjects with previous halothane hepatitis do not appear to be different from controls with regard to drug metabolism and HLA tissue type. The possibility of a higher frequency of complement C3 phenotype F and FS needs further investigation.

Stereoselective inhibition of nortriptyline hydroxylation in man by quinidine.

1. Four volunteers phenotyped as extensive metabolizers of sparteine took 25 mg nortriptyline hydrochloride and collected urine for 72-80 h. Total free and conjugated 10-hydroxynortriptyline (10-OH-NT) accounted for 54-58% of the dose and it was reduced to 25-40% when 50 mg quinidine sulphate was ingested on the first and second day. 2. Of the four isomers of 10-OH-NT, (-)-E-10-OH-NT was selectively decreased in quantity by quinidine coadministration, while the (+)-isomer and (-)- and (+)-Z-10-OH-NT were found in unchanged or slightly increased quantities. The contribution of (-)-E-10-OH-NT to total E-10-OH-NT and the E-/Z-ratio in total 10-OH-NT were significantly reduced. 3. The quantity of the phenol, 2-hydroxynortriptyline in urine was decreased by quinidine; the relative amounts of metabolites with a primary amino group were not affected. 4. Liver microsomes from a donor in which cytochrome P450IID6 was shown to be present by in vitro phenotyping metabolized NT to E-10-OH-NT containing 86% of the (-)-isomer. Quinidine reduced the hydroxylation rate in (-)-E-10-position much more than that in (+)-E-10-position. 5. Since quinidine selectively impairs the function of cytochrome P450IID6, it is concluded that this isoform catalyses NT hydroxylation predominantly in (-)-E-10- and in 2-position.

Lack of pharmacokinetic interaction between nifedipine, sparteine and phenytoin in man.

Nifedipine, sparteine and phenytoin were administered orally to eight healthy subjects separately and as a 'cocktail' on four different occasions to investigate any kinetic interactions. All subjects were extensive metabolizers of sparteine. After drug intake plasma and urine samples were collected up to 32 h and the concentrations of parent drugs and main metabolites were measured. Clearances and formation clearances were not significantly different after single substrate and 'cocktail' administration. Low or non significant correlation coefficients were found between the oxidation of the individual substrates or formation of their metabolites. With this strategy of simultaneous administration of substrates ('cocktail') it appears possible to characterize (and correlate) activities of different cytochrome P-450 isoenzymes, without the disturbing influence of intraindividual variation of drug oxidation with time.

The mephenytoin oxidation polymorphism is partially responsible for the N-demethylation of imipramine

The metabolism of imipramine in six poor metabolizers of mephenytoin was compared with the metabolism of 16 extensive metabolizers of mephenytoin from an earlier study. Each subject was given single doses of 100 mg imipramine hydrochloride and 100 mg desipramine hydrochloride on separate occasions. Imipramine demethylation clearance was 0.74 L.min-1 (mean; range, 0.31-1.24) in poor metabolizers of mephenytoin compared with 1.43 L.min-1 (mean; range, 0.61-3.81) in extensive metabolizers of mephenytoin (p = 0.01, Mann-Whitney U test). It has previously been shown that the imipramine clearance by way of other pathways and desipramine oral clearance, both largely representing 2-hydroxylation, are considerably lower in poor metabolizers of sparteine than in extensive metabolizers of sparteine. In contrast, five subjects who were poor metabolizers of mephenytoin and extensive metabolizers of sparteine and a control group of 11 subjects who were extensive metabolizers of mephenytoin and sparteine showed no statistically significant difference with regard to these parameters. One subject who was a poor metabolizer of mephenytoin and sparteine had the lowest imipramine oral clearance of all 22 subjects studied. In conclusion, this and an earlier study show that the oxidation of imipramine is mediated by means of two different polymorphic P450 isozymes, 2-hydroxylation by way of the sparteine oxygenase (P450IID6) and demethylation by way of the mephenytoin oxygenase (P450IIC8).

Quinidine inhibits the 2-hydroxylation of imipramine and desipramine but not the demethylation of imipramine.

On separate occasions 6 extensive metabolizers of sparteine took a single oral dose of 100 mg imipramine and desipramine before and during the intake of quinidine sulphate 200 mg/day. During quinidine the total oral clearance of imipramine on average was reduced by 35%, and that of desipramine by 85%. The clearance of imipramine via demethylation was not significantly reduced during quinidine administration, whereas its clearance by other pathways, largely 2-hydroxylation, was reduced by more than 50%. 2-OH-Imipramine and 2-OH-desipramine were detected in plasma before (maximum concentrations 30-100 nmol.l-1) but not during quinidine. It appears that quinidine is a potent inhibitor of the sparteine/debrisoquine oxygenase, P450dbl, which is responsible for the 2-hydroxylation of imipramine and desipramine, but not of the P450 isozyme responsible for the demethylation of imipramine.

Mephenytoin and sparteine pharmacogenetics in Canadian Caucasians.

The frequency of genetically deficient hydroxylation of mephenytoin (M-defect) was studied in 83 healthy Caucasians living in Toronto. The M-defect was compared with the widely studied genetic polymorphism of sparteine/debrisoquine oxidations (S-defect). After ingestion of mephenytoin and sparteine, urine samples (0 to 24 hr) were analyzed for p(4')-hydroxymephenytoin and urine samples over 0 to 12 hr were analyzed for sparteine and 2-and 5-dehydrosparteine by gas chromatographic methods. Nirvanol, the N-demethylation product of mephenytoin, was determined by a newly developed gas chromatographic/mass spectrometric method. Frequency distributions of both p-hydroxymephenytoin and dehydrosparteine excreted in urine were discontinuous (bimodal), while nirvanol and sparteine data were normally distributed. Two poor metabolizers of mephenytoin excreted 2% to 3% of the dose as p-hydroxymephenytoin and excreted normal amounts of nirvanol, but they were extensive metabolizers of sparteine. Six poor metabolizers of sparteine were found to be extensive metabolizers of mephenytoin (34% to 42% excreted in urine as p-hydroxyme-phenytoin). Thus the M-defect occurs among Canadian Caucasians with a frequency of 2% (0.0% to 7.5% with a confidence limit of 99%) and is independent of the S-defect.