A population and familial study of the defective alicyclic hydroxylation of debrisoquine among Egyptians

Relevance of pharmacogenetics and pharmacogenomics in veterinary clinical practice: A review

The recent advances in high-throughput next-generation sequencing technologies have heralded the arrival of the Big Data era. As a result, the use of pharmacogenetics in drug discovery and individualized drug therapy has transformed the field of precision medicine. This paradigm shift in drug development programs has effectively reshaped the old drug development practices, which were primarily concerned with the physiological status of patients for drug development. Pharmacogenomics bridges the gap between pharmacodynamics and pharmacokinetics, advancing current diagnostic and treatment strategies and enabling personalized and targeted drug therapy. The primary goals of pharmacogenetic studies are to improve drug efficacy and minimize toxicities, to identify novel drug targets, to estimate drug dosage for personalized medicine, and to incorporate it as a routine diagnostic for disease susceptibility. Although pharmacogenetics has numerous applications in individualized drug therapy and drug development, it is in its infancy in veterinary medicine. The objective of this review is to present an overview of historical landmarks, current developments in various animal species, challenges and future perspectives of genomics in drug development and dosage optimization for individualized medicine in veterinary subjects.

Major CYP450 polymorphism Among Saudi Patients

BACKGROUND

Cytochrome P450 (CYP) contributes to a huge collection of medicinal products' Phase I metabolization. We aimed to summarize and investigate the current evidence regarding the frequency of CYP2D6, CYP2C9, CYP2C19, MDR1 in Saudi Arabia.

METHODS

A computerized search in four databases was done using the relevant keywords. Screening process was done in two steps; title and abstract screening and full-text screening. Data of demographic and characteristics of included studies and patients was extracted and tabulated.

RESULTS

Ten studies were eligible for our criteria and were included in this systematic review. Age of participants ranged between 17-65 years. Only two subjects showed PM phenotype of CYP2C19 in Saudi population. The most frequent alleles were CYP2C19*1 (62.9%), CYP2C19*2 (11.2%-32%), and CYP2C19*17 (25.7%). The CYP2C19m1 was observed in 97 cases of extensive metabolizing (EM) phenotype CYP2C19. Concerning the CYP2C9, the most frequent alleles were CYP2C9*1 and CYP2C9*2, and the most frequent genotype was CYP2C9*1*1. The CYP2D6*41 allele and C1236T MDR1 were the most frequent allele in this population.

CONCLUSION

The current evidence suggests that Saudi Arabians resembled European in the frequency of CYP2C19, Caucasians in both the incidence of CYP2C9 and CYP2C19m1 and absence of CYP2C19m2. The CYP2D6*41 allele frequency in Saudi Arabians is relatively high. We recommend a further research to evaluate the basic and clinical relevance of gene polymorphism in such ethnicity.

Bioinformatics Research on Inter-racial Difference in Drug Metabolism I. Analysis on Frequencies of Mutant Alleles and Poor Metabolizers on CYP2D6 and CYP2C19

The enzyme activities of CYP2D6 and CYP2C19 show a genetic polymorphism, and the frequency of poor metabolizers (PMs) on these enzymes depends on races. In the present study, the frequencies of mutant alleles and PMs in each race were analyzed based on information from published studies, considering the genetic polymorphisms of CYP2D6 and CYP2C19 as the causal factors of racial and inter-individual differences in pharmacokinetics. As a result, it was shown that there were racial differences in the frequencies of each mutant allele and PMs. The frequencies of PMs on CYP2D6 are 1.9% of Asians and 7.7% of Caucasians, and those of PMs on CYP2C19 are 15.8% of Asians and 2.2% of Caucasians. Based on the results, it was suggested that there would be racial differences in the frequencies of PM subjects whose blood concentrations might be higher for drugs metabolized by these enzymes. Additionally, it was suggested that enzyme activities would vary according to the number of functional alleles even in subjects judged to be extensive metabolizers (EMs). In the bridging study, genetic information regarding CYP2D6 and CYP2C19 of the subjects will help extrapolate foreign clinical data to a domestic population.

Pharmacogenetics and psychopharmacotherapy

Response to drugs can vary between individuals and between different ethnic populations. The biological (age, gender, disease and genetics), cultural and environmental factors which contribute to these variations are considered in this review. The most important aspect is the genetic variability between individuals in their ability to metabolize drugs due to expression of 'polymorphic' enzymes. Polymorphism enables division of individuals within a given population into at least two groups, poor metabolisers (PMs) and extensive metabolisers (EMs) of certain drugs. The two most extensively studied genetic polymorphisms are those involving cytochrome P450 2D6 (CYP2D6) and CYP2C19. CYP2D6 metabolizes a number of antidepressants, antipsychotics, beta-adrenoceptor blockers, and antiarrhythmic drugs. About 7% of Caucasians and 1% of Asians are PMs of CYP2D6 substrates. CYP2C19 enzyme participates in the metabolism of omeprazole, propranolol and psychotropic drugs such as hexobarbital, diazepam, citalopram, imipramine, clomipramine and amitriptyline. The incidence of PMs of CYP2C19 substrates is much higher in Asians (15-30%) than in Caucasians (3-6%). Variations in metabolism of psychotropic drugs result in variations in their pharmacokinetic parameters. This may lead to clinically significant intra- and inter-ethnic differences in pharmacological responses. Such variations are discussed in this review. Differential receptor-mediated response may play a role in ethnic differences in responses to antipsychotics and tricyclic antidepressants, but such pharmacodynamic factors remain to be systematically investigated. The results of studies of ethnic differences in response to psychopharmacotherapy appear to be discrepant, most probably due to limitations of study design, small sample size, inadequately defined study sample, and lack of control of confounding factors. The clinical value of understanding pharmacogenetics is in its use to optimize therapeutic efficacy, to prevent toxicity of those drugs whose metabolism is catalysed by polymorphic isoenzymes, and to contribute to the rational design of new drugs. Finally, applications and impact of pharmacogenetics in the field of psychopharmacotherapy are discussed.

Genetic polymorphism of drug metabolising enzymes in African populations: implications for the use of neuroleptics and antidepressants

Metabolism of most drugs influences their pharmacological and toxicological effects. Drugs particularly affected are those with a narrow therapeutic window and that are subjected to considerable first-pass metabolism. Much of the interindividual and interethnic differences in effects of drugs is now attributable to genetic differences in their metabolism. Genetic polymorphisms have been described for many drug-metabolising enzymes in Caucasian and Oriental populations, the most well-characterised being those for cytochrome P450 2D6, cytochrome P450 2C19, glutathione S-transferases, and N-acetyl transferase 2. African populations have been studied to a lesser extent, but it is apparent that populations within Africa are heterogeneous with respect to these polymorphisms. In addition, although some allelic variants are common to all populations throughout the world (e.g., CYP2D6*5), some allelic variants are specific for an African population (e.g., CYP2D6*17). The polymorphisms give rise to enzymes with changed or no activity towards drug substrates. Two of the most important enzymes for metabolism of neuroleptics and other psychoactive drugs are CYP2D6 and CYP2C19. This article compares the current information on polymorphisms of these two enzymes in African and other populations and discusses the implications of these polymorphisms for neuropharmacotherapy.

Influence of smoking in the glutathione-S-transferase M1 deficiency--associated risk for squamous cell carcinoma of the bladder in schistosomiasis patients in Egypt

In this study we show an effect of the glutathione-S-transferase M1 (GSTM1) null phenotype on the risk for squamous cell carcinoma (SCC) of the bladder among male smokers in Egypt, with an adjusted odds ratio of 4.8 (95% confidence interval: 1.06-21.77). However, no overall effect of the GSTM1 null phenotype on the risk for bladder SCC was observed.

Evidence for the polymorphic oxidation of debrisoquine and proguanil in a Khmer (Cambodian) population

The frequency distributions of the urinary metabolic ratios of debrisoquine and proguanil were measured in a population of unrelated Khmers. Out of 98 Khmer subjects studied, two were identified as poor metabolisers of debrisoquine when a metabolic ratio of 12.6 was used as the cut off point. This represents a prevalence of debrisoquine poor metabolisers of 2.1% (95% confidence interval 0.25-7.3%) which is similar to other Asian populations. Based on the distribution of the ratio of proguanil to cycloguanil excreted in urine, and using an antimode value of 10, the prevalence of poor metabolisers of proguanil in a Khmer population was estimated to be 18.4% (95% confidence interval 10.9-28.1%). The frequency of poor metabolisers of proguanil in Khmers was higher than that described for Caucasian populations, but similar to most reported results in Asian populations.

Comparison of the prevalence of the poor metabolizer phenotype for CYP2D6 between 203 Hmong subjects and 280 white subjects residing in Minnesota

Genetic polymorphism of the P450IID6 (CYP2D6) enzyme system can be an important component of the variability in response to drug therapy. Interpopulation differences in the prevalence of deficiencies of drug-metabolizing enzymes may be clinically important in the selection and dosage of drug therapies for patients. Since 1980, the State of Minnesota has had more than a 1000% increase in population of Hmong refugees from Laos. The Hmong are frequently treated in our institution's international clinic with virtually no systematically acquired knowledge about the ability of this relatively ethnically pure population to metabolize commonly used Western medications. To further our knowledge of drug metabolism in this population, we identified the prevalence of the poor metabolizer phenotype for CYP2D6 in a sample population of Hmong subjects and compared this prevalence to that in a sample population of white subjects. Urine collected after ingestion of dextromethorphan in 237 healthy Hmong and 280 healthy white volunteers was analyzed by HPLC. Based on probit plots of the metabolic ratios (dextro-methorphan/dextrorphan), 8.9% of Hmong subjects and 6.1% of white subjects were assigned the poor metabolizer phenotype (difference not significant). Weak associations were found between body surface area and metabolic ratio for both Hmong and white men and between smoking status and metabolic ratio for white subjects only. We conclude that the prevalence of poor metabolizers for the CYP2D6 enzyme system is similar between Hmong subjects and white subjects residing in Minnesota and that an antimode of 0.3 for metabolic ratio appears to be reasonable for the populations studied.

Genetically determined sparteine oxidation polymorphism in a Polish population

The genetic oxidation polymorphism was determined in 160 healthy Polish volunteers from the south-west of Poland (Wrocław region), using sparteine as a model drug. The results of a Polish population study revealed a bimodal distribution of the sparteine metabolic ratio and showed the existence of two oxidation phenotypes designated as extensive and poor metabolizers. The frequency of poor metabolizers in our study (8.8%) compares well with most results of poor oxidation metabolizers in Caucasian populations.

CYP2D6-related oxidation polymorphism in Italy

The distribution of the oxidation polymorphism related to cytochrome CYP2D6 (debrisoquine type) was determined in 246 healthy Italian volunteers. Phenotyping was based on HPLC determination of the dextrometorphan/dextrorphan concentration ratio (metabolic ratio) in urine samples collected over an 8 h interval following a single oral 30 mg dose of dextromethorphan hydrobromide. Urinary excretion of dextromethorphan showed a wide interindividual variability, ranging from < or = 0.04 to 3.9% and from 0.5 to 79.6% of the dose, respectively. Metabolic ratios ranged from < or = 0.001 to 6.6. Eleven of the 246 subjects showed a metabolic ratio greater than 0.30, indicating that 4.5% of the population could be ascribed to the poor metabolizer status. The frequency of the poor metabolizer phenotype in this population is within the range described for other Caucasian ethnic groups.

Dextromethorphan O-demethylation polymorphism in Jordanians

The O-demethylation of dextromethorphan (DMT) to dextrorphan (DRP) was studied in 241 unrelated, healthy Jordanian volunteers (171 males, 70 females). Urine was collected for 8 h following a single oral dose of DMT bromhydrate 30 mg. A thin-layer chromatographic (TLC) technique was used to identify the metaboliser phenotype. The frequency of the poor metaboliser phenotype was found to be 2.9% (approximate 95% confidence interval 0.8-5.0%). Applying the Hardy-Weinberg Law, the frequency of the recessive autosomal gene controlling poor metabolism was 0.17 (95% confidence interval 0.108-0.232).

Debrisoquine oxidation polymorphism in a Tasmanian population

The debrisoquine hydroxylation phenotype was studied in 152 unselected healthy Tasmanian subjects, who were mostly Caucasians of British ancestry. Following a 10 mg oral dose of debrisoquine (D), the ratio of D/4-hydroxydebrisoquine excreted in 8-h urine (metabolic ratio, MR) was determined. MR values were bimodally distributed. Thirteen subjects (8.6%) had MR values from 13.8 to 93.3 and were considered to be poor metabolisers of D, while the others were extensive metabolisers with MR values of 0.04 to 5.4. The D hydroxylation phenotype was not associated with sex. These findings confirm the constancy of D polymorphism in a Caucasian population even after migration to another country.

Evidence for the polymorphic oxidation of debrisoquine in the Thai population

Debrisoquine polymorphism has been studied extensively in Caucasian populations. The prevalence of the poor metaboliser phenotype is 3-10% in European and American Caucasian populations but appears to be very low in Asian populations. This study was carried out to determine the metabolic oxidation status in 173 Thai subjects. Phenotyping was performed using the metabolic ratio (MR) calculated as the 0-8 h urinary output of debrisoquine/0-8 h urinary output of 4-hydroxydebrisoquine after oral administration of 10 mg debrisoquine hemisulphate. Two subjects (1.2%) were phenotyped as poor metabolisers; they had MR values of 13.17 and 92.04. The incidence of the poor metaboliser phenotype of debrisoquine oxidation of 1.2% seems to be lower in the Thai population compared with that in various Caucasian populations.

The genetic polymorphism of debrisoquine/sparteine metabolism--clinical aspects

It has been established that the metabolism of more than twenty drugs, including antiarrhythmics, beta-adrenoceptor antagonists, antidepressants, opiates and neuroleptics is catalyzed by cytochrome P-450dbl. The activity of this P-450 isozyme is under genetic rather than environmental control. This article discusses the therapeutic implications for each of the classes of drugs affected by this genetic polymorphism in drug metabolism. Not only are the problems associated with poor metabolizers who are unable to metabolize the compounds discussed, but it is also emphasized that it is difficult to attain therapeutic plasma concentrations for some drugs in high activity extensive metabolizers.

Polymorphism of the 4-hydroxylation of debrisoquine in the San Bushmen of southern Africa

1. The metabolic oxidation of debrisoquine has been studied in a group of 96 San Bushmen. 2. The amounts of debrisoquine and 4-hydroxy-debrisoquine excreted in 0-8 h urine were measured and the metabolic ratio (% dose as debrisoquine/% dose as 4-hydroxy-debrisoquine) calculated. 3. On the basis of Caucasian criteria, that metabolic ratios greater than 12.6 represent poor metabolizers, 19% of the Bushmen were poor metabolizers in contrast to the 8-10% found in Caucasian studies. 4. Probit plots showed four modes may be present in the data, which may represent at least three isozymes of the relevant enzyme which may also differ from the Caucasian isozymes.

Phenacetin O-deethylase activity of the rat: strain differences and the effects of enzyme-inducing compounds

Phenacetin O-deethylase activity in microsomal fractions from liver of DA and Fischer rats has been determined. No major sex or strain differences were found. Kinetic analysis revealed two major components of O-deethylase activity in the liver of both strains of rats. Michaelis-Menten analysis revealed no major difference between the strains. Phenacetin O-deethylase activity is inducible by both 3-methylcholanthrene and phenobarbitone in DA and Fischer rats. 3-Methylcholanthrene selectively increases the high-affinity component of activity, by 20- to 25-fold, whereas phenobarbitone selectively increases the low-affinity component, by two- to three-fold. It is concluded that there is no major difference between the DA and Fischer strains in their ability to O-deethylate phenacetin. Thus, unlike poor metabolizers of debrisoquine in the human population, who appear also to have impaired phenacetin O-deethylase activity, the DA rat is deficient in only the former activity.

Inter-subject and ethnic differences in paracetamol metabolism

The 24 h urinary excretion of paracetamol and its metabolites following a single oral dose of 1.5 g was compared in 111 Caucasians (Scotland), 67 West Africans (Ghana) and 20 East Africans (Kenya). The fractional recovery of the mercapturic acid and cysteine conjugates of paracetamol was 9.3% in the Caucasians compared with only 5.2% and 4.4% in the Ghanaians and Kenyans respectively (P = less than 0.0005). This probably indicates markedly reduced metabolic activation of paracetamol in the Africans. There were no ethnic differences in the sulphate conjugation of paracetamol, but the mean fractional recovery of the glucuronide conjugate in Caucasians (54%) was significantly less than in the Africans (58%). The sulphate conjugation of paracetamol was increased and glucuronide conjugation reduced in Caucasian females compared with males. A similar trend was seen in the Ghanaians but there were no other significant sex differences. The range of intersubject variation in the metabolic activation of paracetamol was sixty fold compared with only a three fold variation in glucuronide and sulphate conjugation. This has important implications for susceptibility to paracetamol hepatotoxicity following overdosage especially in a small subgroup showing extensive metabolic activation. These ethnic differences in paracetamol metabolism may be related to genetic or environmental factors including differences in diet and protein intake.

Genetics of drug transformation

Biotransformations of drugs are controlled or strongly affected by genetic factors. During the past few years several genetic deficiencies of drug-metabolizing reactions catalyzed by members of the family of cytochrome P-450 were observed. Choice of the appropriate drug to study and attention to urinary metabolites have been the essential ingredients for the recent discovery of genetic deficiencies of drug metabolism in man which include recessive deficiency of debrisoquine/sparteine metabolism and of mephenytoin metabolism. The clinical significance of these defects is discussed. Ethanol after metabolism to acetaldehyde is further metabolized to acetic acid by aldehyde dehydrogenase. Numerous isozymes of aldehyde dehydrogenase exist, one of which possesses a high affinity for acetaldehyde. Approximately 40% of the Oriental population lack this high affinity isozyme so that in these individuals who may have symptoms of flushing and other unpleasant effects the acetaldehyde formed is destroyed only at high plasma concentrations.

Ecogenetics of Parkinson's disease: 4-hydroxylation of debrisoquine

It is postulated that Parkinson's disease is the result of environmental factors acting on genetically susceptible individuals against a background of normal ageing. Many potentially neurotoxic xenobiotics are detoxified by hepatic cytochrome P450. The function of one such system was studied in forty patients with Parkinson's disease and forty normal control subjects. Significantly more parkinsonian than control subjects had partially or totally defective 4-hydroxylation of debrisoquine. Poor metabolisers of debrisoquine tended to have had earlier onset of disease.

Genetically determined variability in acetylation and oxidation. Therapeutic implications

The clinical significance of two separate genetic polymorphisms which alter drug metabolism, acetylation and oxidation is discussed, and methods of phenotyping for both acetylator and polymorphic oxidation status are reviewed. Particular reference is made to the dapsone method, which provides a simple means of distinguishing fast and slow - and possibly intermediate - acetylators, and to the sparteine method which allows a clear separation of oxidation phenotypes. Although acetylation polymorphism has been known for some time, definite indications for phenotyping are few. It is doubtful whether acetylator phenotype makes a significant difference to the outcome in most isoniazid treatment regimens, and peripheral neuropathy from isoniazid in slow acetylators is easily overcome by pyridoxine administration. However, in comparison with rapid acetylators, slow acetylators receiving isoniazid have an increased susceptibility to phenytoin toxicity, and perhaps also to carbamazepine toxicity. It is also possible that rapid acetylators receiving isoniazid attain higher serum fluoride concentrations from enflurane and similar anaesthetics than do similarly treated slow acetylators. Thus, when drug interactions of these types are suspected, phenotyping for acetylator status may be advisable. If routine monitoring of serum procainamide and N-acetylprocainamide concentrations is practised, phenotyping of subjects prior to therapy with these agents should not be necessary. Although acetylator phenotype influences serum concentrations of hydralazine, when this drug is given in combination with other drugs acetylator phenotype has not been shown to influence the therapeutic response. Slow acetylator phenotype along with female gender and the presence of HLA-DR antigens appear to be risk factors in the development of hydralazine-induced systemic lupus erythematosus (SLE). Determination of acetylator phenotype may therefore help determine susceptibility to this adverse reaction. In the case of sulphasalazine, adult slow acetylators require a lower daily dose of the drug than fast acetylators in order to maintain ulcerative colitis in remission without significant side effects. It is therefore advisable to determine acetylator phenotype prior to sulphasalazine therapy. Work on the association of acetylation polymorphism with various disease states is also reviewed. It is possible that a higher incidence of bladder cancer is associated with slow acetylation phenotype - especially in individuals exposed to high levels of arylamines. The question as to whether idiopathic SLE is more common in slow acetylators remains unresolved. There appears to be no difference between fa

Genetic polymorphism of mephenytoin p(4')-hydroxylation: difference between Orientals and Caucasians

The genetically controlled mephenytoin p(4')-hydroxylation capacity was determined in 118 Caucasians and 70 Orientals. After an oral dose of 50 or 100 mg of racemic mephenytoin, the amount of p(4')-hydroxymephenytoin in 24 h urine was measured by gas chromatography. Bimodal distribution was found with 9/70 (13%) Orientals and 5/118 (4%) Caucasians demonstrating deficient p(4')-hydroxylation. The statistically significant difference between Orientals and Caucasians (P less than 0.05) was accounted for by the high incidence of poor metabolizers among the Japanese subjects, 7/31 (23%). The frequency among Chinese subjects, 2/39 (5%), was similar to the frequency among Caucasians.

Inter-ethnic difference in sparteine oxidation among Ghanaians and Germans

Sparteine oxidation, which exhibits genetic polymorphism in various Caucasian populations, was studied in 154 unrelated Ghanaian subjects. Mean total urinary recovery of sparteine and 2- and 5-dehydrosparteines (56.6 +/- 16.6% of the dose) was not different from Caucasians. In contrast to Caucasians, amongst whom 6.3 to 9% of the population are poor metabolizers (PM), no PM subject was observed in the Ghanaian population sample. The data appear to indicate allelic differences between Caucasians and Ghanaians in the gene encoding the synthesis of the P-450 isozyme involved in polymorphic sparteine oxidation.

Statistical analysis of polymorphic drug metabolism data using the Rosin Rammler Sperling Weibull distribution

The Rosin Rammler Sperling Weibull distribution and its use in the analysis of complex data is explained with reference to metoprolol and acebutolol AUC values and isoniazid plasma concentrations. The technique is then applied to sparteine and debrisoquine data to resolve populations into distinct sub-groups. Goodness of fit is measured by applying the chi 2 test to the untransformed data. The method is simple to use and sub-groups can be identified rapidly. Each sub-group can be characterised by a simple exponential equation.

Spectral binding studies of the polymorphically metabolized drugs debrisoquine, sparteine and phenformin by cytochrome P-450 of normal and hydroxylation deficient rat strains

The mechanisms of polymorphic drug hydroxylation of debrisoquine, sparteine and related drugs in vivo have been investigated using Cyt P-450 preparations of inbred rat strains as an in vitro model of the poor and extensive metabolizer phenotypes found in various rat strains and in man. Optical difference spectroscopy with debrisoquine, sparteine, phenformin and three other drugs (selected test compounds with proven or suspected hydroxylation polymorphisms in man) exhibited Type 1 binding in normal Sprague-Dawley, Fischer and Lewis Cyt P-450, whereas no Type I drug binding was found in the hydroxylation deficient DA rat liver Cyt P-450. Cyt P-450 content and Type II drug binding of metiamide was the same in normal and hydroxylation deficient rat liver microsomes. The pronounced Type I drug binding in extensive hydroxylation Cyt P-450 and the defective Type I binding in DA Cyt P-450 in vitro, therefore, closely parallels the polymorphic hydroxylation pattern of these test drugs found in the four rat strains studied in vivo. Consequently, missing binding properties of Cyt P-450 or of its micro-environment might represent the enzymatic defect underlying the genetically determined hydroxylation deficiency of polymorphically metabolized drugs in the poor metabolizer phenotype in the DA rat and, by inference, in man.

Some observations on the oxidation phenotype status of Nigerian patients presenting with cancer

The hypothesis is being explored that there may be an association between genetically determined oxidation status and propensity to develop carcinoma in response to environmental chemical carcinogens. For this purpose, the genetic structure of a normal, healthy Nigerian population with respect to oxidation status, has been compared with that found for a group of 59 Nigerian patients presenting with carcinoma of the liver and gastrointestinal tract. Genetically determined oxidation status was assessed by measuring the extent of oxidation of a probe drug, debrisoquine, to its major metabolite, 4-hydroxydebrisoquine. The cancer group contained a disproportionately large number of individuals who were extensive oxidizers compared to the controls (2 P = 0.0045). The findings support the view that genetically determined oxidation status may be an important host factor in influencing responsiveness to chemical carcinogens that require oxidative metabolic activation.

A study of the debrisoquine hydroxylation polymorphism in a Nigerian population

1. The metabolic oxidation of debrisoquine has been studied in a group of 123 Nigerian volunteers. 2. All subjects excreted unchanged drug together with five oxidation products, namely, 4-, 5-, 6-, 7- and 8-hydroxy-debrisoquine. 3. The 4-hydroxylation reaction exhibits polymorphism; ten subjects were defective in their ability to effect this reaction. 4. The incidence (q) of the allele governing impaired 4-hydroxylation (DL) among Nigerians was calculated as being 0.28 (95% confidence limit of 0.20-0.37). 5. An association was demonstrated between the ability to effect 4-hydroxylation and 6- and 7-hydroxylation of debrisoquine, suggesting that the alleles controlling alicyclic oxidation also influence aromatic hydroxylation.

The polymorphic 4-hydroxylation of debrisoquine in a Saudi arab population

1. Debrisoquine 4-hydroxylation was polymorphic in 102 Saudi arab volunteers, the population comprising one phenotypically poor metabolizer and 101 phenotypically extensive metabolizers of debrisoquine. 2. Mean urinary recoveries of drug and metabolite were low in Saudis (15 +/- 10% dose, mean +/- S.D.), which compared well with previously studied populations of Egyptians (16%) and Ghanaians (18%), but which were lower than those seen in a UK white population (41%). 3. Saudis, like Egyptians, were more extensive metabolizers of debrisoquine than UK whites, as judged by the metabolic ratio (% dose as debrisoquine/% dose as 4-hydroxy-debrisoquine eliminated in the urine). 4. Neither sex, urine collection period nor urinary recovery of drug and metabolite had any statistically significant effect upon the distribution of metabolic ratios in Saudis. 5. The frequency of the DL allele controlling the recessive poor metabolizer trait was 0.099 +/- 0.049 (+/- S.E.M.) in Saudis, which compared well to Egyptians (0.118 +/- 0.059) but was significantly lower than that for UK whites (0.298 +/- 0.030). 6. These findings raise questions regarding the efficacy and safety in Saudis of drugs undergoing oxidative metabolism which have been evaluated for usage in European white subjects.

An evaluation of debrisoquine and mefruside in the treatment of hypertension in African and Indian patients

A double-blind, crossover trial was carried out in 20 hypertensive patients (9 African and 11 Indian) to compare the effectiveness and tolerance of treatment with debrisoquin, mefruside, and a fixed-dose combination of the two drugs with placebo. Patients were treated initially with placebo for 2 weeks before being crossed-over to treatment for 4 weeks with each of the other regimens. Maximum daily dosages of the active drugs were 20 mg debrisoquin and 25 mg mefruside. Satisfactory hypotensive control, i.e. diastolic blood pressure less than or equal to 90 mmHg, was not achieved in any of the treatment periods. The best hypotensive response was obtained in African patients on mefruside. The combination of debrisoquin and mefruside did not produce the expected synergistic response. Few side-effects were reported. The failure of an adequate hypotensive response to debrisoquin in African and Indian patients could be due to a genetic difference in the hydroxylation of debrisoquin.