CYP2D6 genotype determination in the Danish population

Imipramine versus placebo for multiple functional somatic syndromes (STreSS-3): a double-blind, randomised study

BACKGROUND

Functional somatic syndromes, including chronic fatigue syndrome or irritable bowel syndrome, often co-exist. Treatment guidelines supported by high quality evidence exist for most functional somatic syndromes, but are lacking for multiple comorbid functional somatic syndromes. We aimed to assess the effect of the tricyclic antidepressant, imipramine, in patients with multiple functional somatic syndromes defined by the criteria for multiorgan bodily distress syndrome, a unifying diagnosis that encompasses most functional somatic syndromes and somatoform disorders.

METHODS

In this single-centre, double-blind, randomised trial done in a Danish university hospital setting, participants were patients consecutively referred (age 20-50 years) fulfilling criteria for multiorgan bodily distress syndrome with no concurrent comorbid depression or anxiety disorder. Participants were randomly assigned (1:1) to receive either 10 weeks of low-dose imipramine or placebo (oral daily doses of 25-75 mg). The hospital pharmacy handled randomisation (computer-generated) and masking, providing sequentially numbered packs of study drug that were given serially to the participants. All others involved were masked to allocation. Primary outcome was patient-rated overall health improvement on a 5-point clinical global improvement scale. Improvement was defined as patients responding "better" or "much better" as opposed to "unchanged" and "worse" or "much worse" when rating their overall health status after 10 weeks of minimum 25 mg study drug. Analyses included patients who received at least one dose of study drug. This study is registered with ClinicalTrials.gov, number NCT01518634.

FINDINGS

Between Jan 30, 2012, and Nov 24, 2014, 138 patients were randomly assigned; 70 to receive imipramine and 68 to receive placebo. The study was completed on May 1, 2015. 125 patients received at least one dose of study drug: 65 received imipramine and 60 received placebo. Treatment was terminated prematurely for eight (12%) patients receiving imipramine and seven (12%) patients receiving placebo. Data were missing for two (3%) patients receiving imipramine and three (5%) patients receiving placebo. Of the 120 patients (96%) who provided primary outcome data, 33 (53%) receiving imipramine reported their overall health status as "better" or "much better" compared with 14 patients (25%) receiving placebo. The improvement after imipramine was significantly greater than after placebo (odds ratio 3·3 [95% CI 1·6-6·8]; p=0·001). Number needed to treat was 3·6 (95% CI 2·3-8·9). Analysis of the worst-case scenario for patients with missing outcome did not change the interpretation of the results. 32 patients (49%) receiving imipramine and 10 patients (17%) receiving placebo had at least one adverse event of moderate intensity (p=0·0001); eight patients (12%) receiving imipramine and three patients (5%) receiving placebo had at least one adverse event of severe intensity (p=0·1496). One patient (1%) receiving placebo experienced a serious adverse event (a subdural haematoma sustained after an accident). Adverse events caused dropout in four patients (6%) receiving imipramine and three patients (5%) receiving placebo.

INTERPRETATION

Imipramine treatment compared with placebo significantly improved overall health in patients with multiple functional somatic syndromes when both treatments were supported by regular contacts with clinicians. Adverse events were more common in the imipramine group, but only rarely led to discontinuation of treatment.

FUNDING

The Danish Foundation, Trygfonden.

The Impact of Serum Drug Concentration on the Efficacy of Imipramine, Pregabalin, and their Combination in Painful Polyneuropathy

OBJECTIVE

The aim of this study was to explore the serum concentration-effect relation for first-line drugs in neuropathic pain and to determine if efficacy could be increased.

METHODS

Data from a randomized, placebo-controlled, cross-over trial on imipramine, pregabalin, and their combination in painful polyneuropathy were used. Treatment periods were of 4 weeks' duration, outcome was the weekly median of daily pain rated by a 0 to 10 numeric scale, and drug concentrations were determined by high-performance liquid chromatography.

RESULTS

In 47 patients, pain was reduced -1.0 (95% confidence interval [CI], -1.5 to -0.6) by imipramine, -0.4 (95% CI, -0.9 to 0.1) by pregabalin, and -1.6 (95% CI, -2.1 to -1.1) by combination therapy. On monotherapy, there was no difference between responders and nonresponders with respect to concentrations of imipramine (mean, 161 vs. 229 nmol/L, P=0.129) and pregabalin (mean, 9.8 vs. 11.7 μmol/L, P=0.178). There was no correlation between drug concentration and pain reduction for imipramine (r=0.17, P=0.247), whereas there was a marginally, positive correlation for pregabalin (r=0.28, P=0.057). There was no interaction between treatment and concentration classes (imipramine < or ≥100 nmol/L, pregabalin < or ≥10 μmol/L) either for monotherapy or for combination therapy (P=0.161 to 0.797). Isobolographic presentations of reponders with imipramine and pregabalin concentrations during combination therapy did not indicate synergistic interaction.

DISCUSSION

There were no important relations between drug concentrations and efficacy, or indication of synergistic interaction between the drugs. It was not concluded that treatment can be improved by measurement of drug concentration of pregabalin.

Imipramine and pregabalin combination for painful polyneuropathy: a randomized controlled trial

Monotherapy with first-line drugs for neuropathic pain often fails to provide sufficient pain relief or has unacceptable side effects because of the need for high doses. The aim of this trial was to test whether the combination of imipramine and pregabalin in moderate doses would relieve pain more effectively than monotherapy with either of the drugs. This was a randomized, double-blind, placebo-controlled, crossover, multicenter trial consisting of four 5-week treatment periods in patients with painful polyneuropathy. Treatment arms were imipramine 75 mg/d vs pregabalin 300 mg/d vs combination therapy vs placebo. Patients with polyneuropathy and symptoms for more than 6 months, age 20 to 85 years, pain intensity ≥4 on a 0- to 10-point numeric rating scale (NRS) and pain at least 4 days a week were included in the trial. A total of 262 patients were screened for participation, 73 patients were randomized, and 69 patients were included in the data analysis. The effect on average pain in comparison with placebo was: combination (-1.67 NRS points, P < 0.001), imipramine (-1.08 NRS points, P < 0.001), and pregabalin (-0.48 NRS points, P = 0.03). The combination therapy had significantly lower pain scores than both monotherapies: combination vs imipramine (P = 0.009), combination vs pregabalin (P < 0.001). During combination therapy, the dropout rate was higher and the patients reported a higher rate and severity of side effects. Combination of moderate doses of the tricyclic antidepressant imipramine and pregabalin could be considered as an alternative to high-dosage monotherapy. However, the trial also emphasized that balance between efficacy and safety is an issue.

Pharmacogenetics of drug oxidation via cytochrome P450 (CYP) in the populations of Denmark, Faroe Islands and Greenland

Denmark, the Faroe Islands and Greenland are three population-wise small countries on the northern part of the Northern Hemisphere, and studies carried out here on the genetic control over drug metabolism via cytochrome P450 have led to several important discoveries. Thus, CYP2D6 catalyzes the 2-hydroxylation, and CYP2C19 in part catalyzes the N-demethylation of imipramine. The phenomenon of phenocopy with regard to CYP2D6 was first described when Danish patients changed phenotype from extensive to poor metabolizers during treatment with quinidine. It was a Danish extensive metabolizer patient that became a poor metabolizer during paroxetine treatment, and this was due to the potent inhibition of CYP2D6 by paroxetine, which is also is metabolized by this enzyme. Fluoxetine and norfluoxetine are also potent inhibitors of CYP2D6, and fluvoxamine is a potent inhibitor of both CYP1A2 and CYP2C19. The bioactivation of proguanil to cycloguanil is impaired in CYP2C19 poor metabolizers. The O-demethylation of codeine and tramadol to their respective my-opioid active metabolites, morphine and (+)-O-desmethyltramadol was markedly impaired in CYP2D6 poor metabolizers compared to extensive metabolizers, and this impairs the hypoalgesic effect of the two drugs in the poor metabolizers. The frequency of CYP2D6 poor metabolizers is 2%-3% in Greenlanders and nearly 15% in the Faroese population. The frequency of CYP2C19 poor metabolizers in East Greenlanders is approximately 10%. A study in Danish mono and dizygotic twins showed that the non-polymorphic 3-N-demethylation of caffeine catalyzed by CYP1A2 is subject to approximately 70% genetic control.

Ecstasy use and serotonin syndrome: a neglected danger to adolescents and young adults prescribed selective serotonin reuptake inhibitors

BACKGROUND

At present, there are scarce clinical and basic lab data concerning the risk of acute serotonin toxicity from selective serotonin reuptake inhibitors (SSRIs) and 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) co-administration. The health care community can strongly benefit from efforts to address the high risks associated with serotonin syndrome from this specific drug combination.

OBJECTIVE

The aim of this work is to review the risk of serotonin syndrome in adolescents and young adults prescribed with SSRIs and are concurrently using ecstasy.

DATA SOURCES

An electronic search of the major behavioral science bibliographic databases (Pubmed, PsycINFO, Medline) was conducted to retrieve peer-reviewed articles, which detail the clinical characteristics, biological mechanisms and social implications of SSRIs, MDMA, and their potential synergism in causing serotonin syndrome in the pediatric and young adult population. Search terms included "serotonin syndrome", "ecstasy", "MDMA", "pediatric", and "SSRI". Additional references were incorporated from the bibliographies of these retrieved articles.

RESULTS

MDMA, in combination with the widely-prescribed SSRI antidepressant class, can lead to rapid, synergistic rise of serotonin (5-HT) concentration in the central nervous system, leading to the acute medical emergency known as serotonin syndrome. This review addresses such complication through an exploration of the theoretical mechanisms and clinical manifestations of this life-threatening pharmacological interaction.

CONCLUSION

The increasing incidences of recreational ecstasy use and SSRI pharmacotherapy among multiple psychiatric disorders in the adolescent population have made this an overlooked yet increasingly relevant danger, which poses a threat to public health. This can be curbed through further research, as well as greater health care provision and attention from a regulatory body owing.

Alternative reliable method for cytochrome P450 2D6 poor metabolizers genotyping

High-resolution melting curve analysis (HRM) of polymerase chain reaction (PCR) amplicons has been described as a fast, cheap, and reliable closed-tube method of genotyping with no need for labeled primers or labeled probes. We adapted this melting analysis assay for the detection of the most common nonfunctional alleles of cytochrome P-450 (CYP) 2D6 in the Caucasian population that affect the metabolism of many commonly used drugs. We used this method to genotype 91 patients under paroxetine therapy. The presence and the constitution of the most common single-nucleotide polymorphisms (1846G>A, 2988G>A, 100C>T, 2549delA, 2615_2617delAAG, and 1707delT) in poor and intermediate metabolizers from the Caucasian population were detected in short amplicons (≤148 bp). After fluorescence normalization, the wild-type, homozygous, and heterozygous samples were easily distinguishable from each other by their specific melting curve shape. A total of 92.6% of the 1846G>A heterozygotes, 96% of the 100C>T heterozygotes, and 100% of the 2988G>A, 2549delA, 2615_2617delAAG, and 1707delT heterozygotes have been correctly distinguished from the wild types. One hundred percent of all the homozygotes in this group of patients have been detected without any error. HRM of short amplicons is a simple tool for effective, rapid, and reliable CYP2D6 genotyping that does not require real-time PCR, labeled probes, processing or any separations after PCR. The reaction is performed in a closed-tube system and is highly specific and sensitive. We proved that this technique is highly reliable for use in routine diagnostics.

Therapeutic drug monitoring of non-tricyclic antidepressant drugs

Therapeutic drug monitoring (TDM) of many of the tricyclic antidepressants (TCAs) has been demonstrated to be of clear clinical value. This article reviews studies of TDM for the selective serotonin reuptake inhibitors (SSRIs) and other non-tricyclic antidepressants such as venlafaxine, nefazodone, trazodone, mianserin and bupropion. No definitive therapeutic concentrations have been demonstrated for these agents, nor have levels indicative of toxicity been reported. The major benefit of TDM for these agents would appear to be in the assessment of the apparently treatment-refractory depressed patient, to determine whether such lack of response is related to inadequate levels that would suggest either poor compliance, ultra-rapid metabolism, or drug interactions leading to induction of metabolising enzymes. Potential future applications of TDM, in conjunction with genotyping of cytochrome P450 enzymes and pharmacogenomic evaluations, are discussed.

Oral lichen planus and intake of drugs metabolized by polymorphic cytochrome P450 enzymes

OBJECTIVE

To study if patients with oral lichen planus (OLP) had a medication profile different from that of a control group without oral mucosal lesions. It was hypothesized that OLP lesions might result from poor drug metabolism (PM) because of genetic variation of the major cytochrome P450-enzymes (CYPs with a PM-risk).

SUBJECTS AND METHODS

Dental records of 172 OLP patients were reviewed in this cross-sectional study and 152 sex- and age-matched subjects served as controls. The measures for the drug profiles were medicine type (ATC-code), mono- and polypharmacy, CYP-enzyme metabolism pattern, and medicine with a potential to induce lichenoid drug eruptions.

RESULTS

Fifty per cent of the OLP patients consumed daily medications as compared with 59% of the controls. The OLP patients more frequently consumed medicines metabolized by CYPs with a PM-risk (P = 0.03). Furthermore, they consumed more medicine with an inhibitory effect on one or more CYPs than the controls (P = 0.01).

CONCLUSION

Confounders like sex, age, systemic diseases, drug distribution into the therapeutic classes, and polypharmacy were similar in the two groups; but the OLP patients consumed more drugs metabolized by CYPs with a PM-risk. The results argue for further investigation of associations between OLP, medication intake and the CYP-enzyme metabolic pathways.

Pharmacogenetic screening and therapeutic drugs

BACKGROUND

Pharmacogenetics is the science of the influence of heredity on pharmacological response.

ISSUES

The cost of severe adverse drug reactions in individuals has been estimated in the US alone to be in excess of US$4 billion. It has been argued that in a significant proportion of cases, the efficacy and toxicity profiles of drug therapy would be substantially improved in individuals if characteristics due to genetic variation were taken into account. Methods are now available, which make screening for susceptibility feasible.

CONCLUSIONS

There are several therapeutic areas in which screening may give rise to significant improvements in outcome with cost-benefits to both the individual and the community. However, there is currently a lack of data on which cost-benefit analysis can be based. The challenge is to provide this information for new drugs, and for drugs with established therapeutic roles.

Pharmacogenetics: a new diagnostic tool in the management of antidepressive drug therapy

Pharmacogenetics studies the genetic basis of an individual's ability to respond to pharmacotherapy. Variability of this response is a major problem. Fatal adverse drug reactions have been reported to be the fourth leading cause of death in the US. In depression, 30-40% of all patients do not respond sufficiently to the initial treatment and it can take up to 6 weeks for them to be identified. Much knowledge has been gathered throughout the last 3 decades about the genetic basis of pharmacokinetic variability. Genetic tests suitable for the routine laboratory are now available for some important metabolizing enzymes (e.g., CYP2D6, CYP2C19) identifying those individuals who are slow or fast metabolizers of certain drugs, many of which are widely used in the treatment of depression (e.g., tricyclic antidepressants). The possible use of these tests in the clinical practice of monitoring antidepressant therapy is discussed in relation to older phenotyping methods and therapeutic drug monitoring.Less well studied than the genetics of pharmacokinetics is the genetic basis of pharmacodynamic variability. As selective serotonin reuptake inhibitors (SSRI) have a wide therapeutic index, pharmacokinetic variability usually does not explain insufficient response to therapy. Recently, some excitement was caused by reports on serotonin transporter gene polymorphisms and their influence on the response to antidepressive therapy with SSRIs as this could provide an interesting diagnostic tool in assessing the chances of response to the most popular group of antidepressants at present. Current knowledge in this young field of research is summarized.

CYP2D6 gene polymorphism in caucasian smokers: lung cancer susceptibility and phenotype-genotype relationships

Individual susceptibility to smoking-related cancers is proposed to partly depend on a genetically determined ability to metabolise tobacco carcinogens. We previously reported on the association between the activity of the xenobiotic-metabolising enzyme CYP2D6 and lung cancer risk in a hospital-based case-control study among French Caucasian smokers. Here we extended the study to address the effect of four gene-inactivating mutations (CYP2D6(*)3, (*)4, (*)5 and (*)16) and the gene duplication of the CYP2D6 gene (CYP2D6(*)2x2 or CYP2D6(*)1x2) on lung cancer risk in the same population (150 patients with primary lung carcinoma of squamous cell or small cell histology and 172 controls). The risk of lung cancer associated with the CYP2D6 poor metaboliser genotype (odds ratio 1.5, 95% confidence interval 0.5-4.3) did not differ from that in the reference category of extensive metaboliser and ultra-rapid metaboliser genotypes combined. Lung cancer risks for the CYP2D6 PM genotype amongst light smokers (tobacco consumption </=20 g/day) or heavy smokers (>20 g/day) were not significantly different. The present findings agree with the discrepancy between the phenotype-based and genotype-based studies indicated by the recent meta-analyses.

Therapeutic drug monitoring of psychotropic medications

Therapeutic drug monitoring (TDM) of a number of psychotropic medications has proven to be of value, enabling minimization of the limitations of considerable genetic variability in their metabolism and the high rates of poor compliance with many psychiatric disorders. Therapeutic ranges have been established for lithium, some of the tricyclic antidepressants, and clozapine. TDM has also been shown to be useful in avoiding toxicity (as many psychotropics have narrow therapeutic indices), particularly that due to interactions with other compounds.

Pharmacogenetic methods as a complement to therapeutic monitoring of antidepressants and neuroleptics

A short review of the metabolism of psychoactive drugs and the pharmacogenetic factors regulating the enzymes involved is presented here. The potential clinical usefulness of phenotyping and genotyping individuals, with regard to their drug metabolic capacity, is discussed. Indications for genotyping CYP2D6 and a flow scheme for the combined use of conventional therapeutic drug monitoring (TDM) and pharmacogenetic methods for optimizing dosage-schedules of psychoactive drugs are suggested.

Phenotypes and genotypes for CYP2D6 and CYP2C19 in a black Tanzanian population

AIMS

CYP2D6 and CYP2C19 are polymorphically expressed enzymes that show marked interindividual and interethnic variation. The aim of this study was to determine the frequency of the defective alleles in CYP2D6 and CYP2C19 in Africans and to test whether the genotype for CYP2C19 is better correlated with the proguanil/cylcoguanil ratio than the mephenytoin S/R ratio.

METHODS

Two hundred and sixteen black Tanzanians were phenotyped for CYP2D6 with the use of sparteine, and for CYP2C19 with the use of mephenytoin and proguanil. Of these 196 subjects were also genotyped for CYP2D6 (including the CYP2D6*1, CYP2D6*3 and CYP2D6*4 alleles) and 195 were genotyped for CYP2C19 (including the CYP2C19*1, CYP2C19*2 and the CYP2C19*3 alleles). Furthermore 100 subjects were examined for the allele duplication in CYP2D6, leading to ultrarapid metabolism, with long PCR.

RESULTS

The sparteine metabolic ratio (MR) was statistically significantly higher in the Tanzanian group of homozygous, extensive metabolizers compared to a historical control group of white Danish extensive metabolizers. Only one poor metabolizer for CYP2D6 (MR=124 and genotype CYP2D6*1/CYP2D6*4 ) was found. The gene frequencies were 0.96 for the CYP2D6*1 allele and 0.04 for the CYP2D6*4 allele. No CYP2D6*3 alleles were found. Nine subjects had an allele duplication in CYP2D6 (9%). For CYP2C19 there were seven subjects (3. 6%) who were phenotyped as poor metabolizers, but only three subjects (1.5%) had a genotype (CYP2C19*2/CYP2C19*2 ) indicative of poor metabolism. The gene frequencies were 0.90 for the CYP2C19*1 allele and 0.10 for the CYP2C19*2 allele. No CYP2C19*3 alleles were found. The mephenytoin S/R ratios were not bimodally distributed.

CONCLUSIONS

Both the genotyping and phenotyping results show that there is a substantial difference between an African black population and a Caucasian population in the capacity to metabolize drugs via CYP2D6 and CYP2C19.

Optimizing drug therapy based on genetic differences: implications for the clinical setting

Differences in drug responses due to gene alterations are rapidly being identified. Gene alterations may inhibit the function of an enzyme so that an active drug accumulates, causing adverse reactions with normal doses. Alternatively, gene alterations may accelerate enzymatic function so that an active drug is rapidly eliminated, causing subtherapeutic responses to normal doses. Mutations and polymorphisms have been identified that affect a person's response to many currently prescribed medications including cardiovascular, anti-infective, chemotherapeutic, psychiatric, and analgesic drugs. The potential exists for drug therapy to be optimized by selecting medication and doses based on a person's genotype rather than by trial and error. In the near future, advanced practice nurses in the acute care setting may be expected to order, provide patient education about, and explain results of genetic tests before initiating a specific drug therapy. Advanced practice nurses must be knowledgeable about what genetic tests are analyzing and their benefits, limitations, and risks.

Serotonin syndrome: history and risk

This review focuses on the history of investigations into the behavioural reaction resulting from excess stimulation of post-synaptic 5-hydroxytryptamine receptors and the relative risk of this occurring with different combinations of drugs. Other aspects, particularly treatment with 5-hydroxytryptamine receptor antagonists, are reviewed in a recent separate paper [44]. The first human case was in 1955 and animal work had defined the characteristic features by 1958, and established they were lessened by chlorpromazine. Substantial evidence of a 'dose-effect' relationship existed by 1984. The relative risk with different drug combinations is assessed from available evidence and argued to be strongly associated with the degree of elevation of 5-hydroxytryptamine, which is greatest following combinations of irreversible inhibitors of monoamine oxidase A and B with potent serotonin reuptake inhibitors. The various serotonergic drugs that may be implicated in serotonin syndrome are tabulated and discussed in relation to the relative risk. It is suggested that the proposed 'diagnostic criteria' for serotonin syndrome are inappropriate since there is a continuous spectrum from side effects to toxicity. The term 'serotonin syndrome' may encourage the presumption that it is an idiosyncratic response, as neuroleptic malignant syndrome is usually considered to be. The terms 'toxic serotomimetic reaction' or 'toxic serotonin syndrome' may be preferable alternatives. The differences between serotonin syndrome and neuroleptic malignant syndrome are highlighted with examples from difficult or questionable cases in the recent literature. It is proposed that more systematic national collection of toxicity data is essential in order to quantify the relative risk of serotonin syndrome with various combinations of serotonergic drugs.

Molecular mechanisms of genetic polymorphisms of drug metabolism

One of the major causes of interindividual variation of drug effects is genetic variation of drug metabolism. Genetic polymorphisms of drug-metabolizing enzymes give rise to distinct subgroups in the population that differ in their ability to perform certain drug biotransformation reactions. Polymorphisms are generated by mutations in the genes for these enzymes, which cause decreased, increased, or absent enzyme expression or activity by multiple molecular mechanisms. Moreover, the variant alleles exist in the population at relatively high frequency. Genetic polymorphisms have been described for most drug metabolizing enzymes. The molecular mechanisms of three polymorphisms are reviewed here. The acetylation polymorphism concerns the metabolism of a variety of arylamine and hydrazine drugs, as well as carcinogens by the cytosolic N-acetyltransferase NAT2. Seven mutations of the NAT2 gene that occur singly or in combination define numerous alleles associated with decreased function. The debrisoquine-sparteine polymorphism of drug oxidation affects the metabolism of more than 40 drugs. The poor metabolizer phenotype is caused by several "loss of function" alleles of the cytochrome P450 CYP2D6 gene. On the other hand, "ultrarapid" metabolizers are caused by duplication or amplification of an active CYP2D6 gene. Intermediate metabolizers are often heterozygotes or carry alleles with mutations that decrease enzyme activity only moderately. The mephenytoin polymorphism affects the metabolism of mephenytoin and several other drugs. Two mutant alleles of CYP2C19 have so far been identified to cause this polymorphism. These polymorphisms show recessive transmission of the poor or slow metabolizer phenotype, i.e. two mutant alleles define the genotype in these individuals. Simple DNA tests based on the primary mutations have been developed to predict the phenotype. Analysis of allele frequencies in different populations revealed major differences, thereby tracing the molecular history and evolution of these polymorphisms.

An additional allelic variant of the CYP2D6 gene causing impaired metabolism of sparteine

The identification of a novel CYP2D6 allele from a healthy Caucasian poor metabolizer was achieved by using a previously described polymerase chain reaction/single-strand conformation polymorphism strategy. Among the four point mutations that this allele carries, a missense mutation in exon 1 (212 G-->A or D6-H) seems to be responsible for the loss of CYP2D6 function. Although the mutation D6-H has a low prevalence in a randomly selected population of healthy Caucasians, its identification should further increase the phenotype prediction rate by genotyping.

Debrisoquin and S-mephenytoin hydroxylation phenotypes and CYP2D6 genotypes in an Estonian population

The polymorphisms of debrisoquin (CYP2D6) and S-mephenytoin (CYP2C19) hydroxylation were studied in 210 unrelated healthy native Estonians by coadministration of mephenytoin and debrisoquin or dextromethorphan. Among the 210 volunteers 21 (10%) were poor metabolizers of debrisoquin/dextromethorphan and two (0.95%) were poor metabolizers of S-mephenytoin. By pooling these data with an earlier study on 156 Estonians, the prevalences of poor metabolizers of debrisoquin/dextromethorphan and poor metabolizers of S-mephenytoin were 7.6% and 2.2%, respectively. The CYP2D6 genotype of 151 subjects was analysed by allele-specific PCR amplification for the defect alleles CYP2D6A and CYP2D6B. All poor metabolizers of debrisoquin carried two defect CYP2D6-alleles. The phenotype (extensive or poor metabolizer) was in all subjects correctly predicted by the genotype. The frequencies of the defect alleles CYP2D6B and CYP2D6A among these 151 subjects (including 14 poor metabolizers-9.3%) were 21.5% and 2.3%, respectively. DNA from 6 subjects with very high CYP2D6 activity (debrisoquin MR < 0.1) was analysed by EcoRI RFLP to identify duplicated or amplified CYP2D6-genes. Two of the subjects were found to carry a duplicated CYP2D6L-gene. In conclusion, the distribution of genetically determined metabolic capacities of CYP2D6 and CYP2C19 in Estonian unrelated subjects did not differ significantly from that in other Caucasian populations. The CYP2D6 phenotype was predicted by PCR-based amplification for the CYP2D6A and CYP2D6B-alleles.

The CYP2D6 genotype predicts the oral clearance of the neuroleptic agents perphenazine and zuclopenthixol

BACKGROUND

Most antidepressant and neuroleptic agents are metabolized by the polymorphic cytochrome P450 enzyme CYP2D6. This study evaluates the importance of the CYP2D6 genotype for the disposition of the neuroleptic agents perphenazine and zuclopenthixol.

METHODS

Patients treated with neuroleptic agents (n = 36) were studied prospectively with regard to CYP2D6 genotype and neuroleptic plasma concentration during oral treatment. Because no patient provided enough samples for individual kinetic modeling, a bayesian approach was used for determination of the clearance. Population kinetic parameters for this procedure were collected from retrospective therapeutic drug monitoring data (n = 113) by use of a nonparametric approach.

RESULTS

The CYP2D6 genotype significantly predicted the oral clearance of perphenazine and zuclopenthixol (p < 0.01 by multiple regression). The difference in clearance between homozygous extensive metabolizers and poor metabolizers was threefold for perphenazine and twofold for zuclopenthixol.

CONCLUSION

The results show that the genotype for CYP2D6 is closely related to the oral clearances of perphenazine and zuclopenthixol. If this finding can be confirmed in a larger population, genotyping may become an important tool for the dosing of these two neuroleptic agents.

Steady-state plasma levels of nortriptyline and its 10-hydroxy metabolite: relationship to the CYP2D6 genotype

The relationship between the CYP2D6 genotype and the steady state plasma levels of nortriptyline (NT), its main active metabolite 10-hydroxynortriptyline (10-OH-NT) and the NT/10-OH-NT ratio were studied in 21 Caucasian depressed patients treated with 100-150 mg NT daily. The patients had participated in a previously published study investigating the role of NT and 10-OH-NT for the therapeutic effect of NT, and the plasma level data were from that study. In the present follow-up study, the patients were genotyped with respect to the polymorphic CYP2D6 by allele-specific PCR amplification and EcoRI RFLP. One poor metabolizer (PM) was identified and she had the highest plasma concentration of NT. Among the 20 extensive metabolizers (EM), the genotype (homozygous versus heterozygous EM) alone was not found to explain the variance in dose-corrected NT concentrations, but contributed significantly when gender was also taken into account. Together, these factors accounted for 59% of the variability in NT levels. Female patients had higher plasma levels of NT than male patients. 10-OH-NT levels were influenced by genotype, and NT/10-OH-NT ratio by genotype and gender. The present follow-up study confirms a relationship between the CYP2D6 genotype and the plasma levels of NT and its active metabolite. Identification of PM by genotyping should be of value for the prediction of the plasma levels and, consequently, the lower than average dose of NT required for optimal therapy. Also among EM, the genotype contributes to the variability in NT and 10-OH-NT levels but alone is of limited practical value for the prediction of optimal dosage.

Imipramine metabolism in relation to the sparteine and mephenytoin oxidation polymorphisms--a population study

1. Sparteine and mephenytoin phenotyping tests were carried out in 327 healthy Danish subjects. Two weeks 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 h.p.l.c. 2. The medians of the hydroxylation ratios (i.e. 2-hydroxy-metabolite over parent compound) were 6 to 14 times higher in 300 extensive metabolizers of sparteine (EMs) as compared with 27 poor metabolizers (PMs), but none of the ratios separated the two phenotypes completely. 3. There were 324 EM of mephenytoin (EMM) and three PM (PMM) in the sample. The demethylation ratios between desipramine, 2-hydroxy-desipramine and their corresponding tertiary amines showed statistically significant correlations with the mephenytoin S/R isomer ratio (Spearman's rs: -0.20 and -0.27, P < 0.05). 4. The demethylation ratios were higher in 80 smokers than in 245 non-smokers. This indicates that CYP1A2, which is induced by cigarette smoking, also catalyzes the N-demethylation of imipramine. 5. CYP2D6 genotyping was carried out by PCR in 325 of the subjects, and the D6-wt allele was amplified in 298 EMs, meaning that they were genotyped correctly. One PMs was D6-wt/D6-B, another PMs had the genotype D6-wt/ and hence both were misclassified as EMs. The remaining 25 PMs were D6-A/D6-B (n = 5), D6-B/ (n = 18) or D6-D/D6-D (no PCR amplification, n = 2).(ABSTRACT TRUNCATED AT 250 WORDS)