A family and population study of the genetic polymorphism of debrisoquine oxidation in a white British population

Metabolic oxidation of methaqualone in extensive and poor metabolisers of debrisoquine

The metabolism of methaqualone to the glucuronides of 5 C-monohydroxy metabolites and to the N-oxide has been studied in 2 groups of healthy young adults phenotyped as extensive and poor metabolisers of debrisoquine. No significant interphenotype differences were observed with respect to the excretion of any of the 6 metabolites. It is probable that the genetic regulation of the pathways leading to these metabolites is at a locus other than that which is responsible for the regulation of the oxidation of debrisoquine, guanoxan, phenacetin, phenytoin and sparteine.

The genetic control of bufuralol metabolism in man

Bufuralol (Ro 3 - 4787, Angium) is a non selective beta-adrenoceptor blocking drug with some degree of sympathomimetic action and a longer duration of action than propranolol. Plasma concentrations of bufuralol and 1'-hydroxybufuralol, its main blood derivative which shows similar beta-adrenoceptor blocking properties, were determined in healthy volunteers after a 60 mg oral and a 20 mg intravenous dose. Peak plasma concentrations were higher for the parent drug but due to a longer elimination half-life, the metabolite concentrations became higher after a few hours (bufuralol t 1/2 = 2.7 +/- 0.9 h, metabolite t 1/2 = 6.1 +/- 1.5h). The bioavailability of the tablet tested was 46 +/- 15%. The occurrence of side-effects in a subject with abnormal pharmacokinetics of the drug in this study and in a previous study with this drug suggested the possibility of a pharmacogenetic anomaly. Determination of the plasma metabolic ratio in the family of this subject and in a larger population confirmed that aliphatic hydroxylation of bufuralol is under polymorphic control. Phenotyping of our volunteers with debrisoquine showed the present pharmacogenetic anomaly to be the same as the one reported for debrisoquine alicyclic hydroxylation. The occurrence of side-effects in poor metabolizers as seen with bufuralol illustrates the clinical relevance of the hydroxylation polymorphism. In Switzerland the frequency of poor metabolizers is about 9% as previously reported for caucasian British subjects.

Animal modelling of human polymorphic drug oxidation--the metabolism of debrisoquine and phenacetin in rat inbred strains

The metabolism of debrisoquine (5 mg kg-1 orally) was investigated in females of 7 strains of rat. Two major metabolic pathways, those of 4- and 6-hydroxylation were found to be polymorphic. The DA strain eliminated in urine only 7-10% of the dose as 4-hydroxy-debrisoquine together with 31-55% debrisoquine while the corresponding values for the Lewis strain were 44-55% and 11-17% respectively. Accordingly, DA and Lewis rats were proposed as models for the human PM (poor metabolizer) and EM (extensive metabolizer) drug oxidation phenotypes. To further test this model, DA and Lewis rats were given phenacetin (200 mg kg-1 orally). This underwent O-de-ethylation to paracetamol (52-55%) and aromatic 2-hydroxylation (7-8%) in Lewis rats. The corresponding findings in DA rats were 35-40% O-de-ethylation and 12-13% 2-hydroxylation. It is suggested that, with respect to both debrisoquine and phenacetin, Lewis and DA inbred rat strains afford a model of oxidative drug metabolism for the human EM and PM phenotypes respectively.

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.