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.

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

A population survey of 258 unrelated white British subjects showed a polymorphism for the 4-oxidation of debrisoquine. "Extensive metabolisers" (EM) and "poor metabolisers" (PM) are recognisable, 8.9% of the population being PM. Nine pedigrees ascertained through PM probands show that the PM phenotype is an autosomal Mendelian recessive character. The EM phenotype is dominant and the degree of dominance has been estimated at 30%. PM subjects are more prone to hypotension during debrisoquine therapy. The alleles controlling this polymorphism appear to control the oxidation of other drugs.

Debrisoquin hydroxylation polymorphism among Ghanaians and Caucasians

The alicyclic and aromatic hydroxylation of debrisoquin was studied in Ghanaians. As in a previously studied Caucasian population, the alicyclic 4-hydroxylation of debrisoquin in Ghanaians was polymorphic. Three phenotypes were observed: homozygous extensive metabolizers (58%), heterozygous extensive metabolizers (36%), and homozygous poor metabolizers (6%). In contrast, British Caucasians are primarily monomorphic extensive metabolizers (92%) and homozygous poor metabolizers comprise 8% of the population. Urinary recovery of the drug and its hydroxylated metabolites was significantly less in the Ghanaian subjects. In both Ghanaian and British populations, aromatic hydroxylation producing 5-, 6-, 7-, and 8-hydroxydebrisoquin was shown to parallel the alicyclic 4-hydroxylation of debrisoquin, and thus to be controlled by the same gene locus. Debrisoquin is advocated as a tool for uncovering polymorphism in drug oxidation and its interethnic variations.

Interindividual and interspecies variation in the metabolism of the hallucinogen 4-methoxyamphetamine

1. The qualitative and quantitative aspects of the urinary elimination of orally administered 4-methoxy[14C]amphetamine have been examined in the rat and guinea-pig and in three volunteer human subjects, to determine interspecies and interindividual variations in disposition of the drug. 2. Both rat and guinea-pig excreted 70--80% of the administered dose(6 mg/kg) in the urine within 24 h, mainly as metabolites. 3. In the guinea-pig, the drug was metabolized by O-demethylation to give 4-hydroxyamphetamine, which was excreted free (4% dose) and conjugated (73%). No other metabolite was detected. 4. The rat metabolizes the drug both by O-dealkylation and by side-chain oxidation, the products being 4-hydroxyamphetamine (5% of dose free and 60% conjugated) and 1-(4'-methoxyphenyl)propan-2-one oxime (5% dose, free and conjugated). 5. In man the drug (dose 5 mg) is metabolized by O-demethylation and by side-chain oxidation. Marked intersubject variations were observed both in the array and quantitative aspects of metabolite excretion. Two subjects excreted mainly 4-hydroxyamphetamine (free and conjugated) together with smaller amounts of 1-(4'-methoxyphenyl)propan-2-one oxime and 4-hydroxynorephedrine. The third subject, however, who was previously known to exhibit a genetically determined defect in drug oxidation, was defective in O-dealkylation of 4-methoxyamphetamine, and the main excretion products were the unchanged drug together with products of side-chain oxidation, namely, 1-(4'-methoxyphenyl)propan-2-one oxime, 1-(4'-methoxyphenyl)propan-2-one and 4-methoxybenzoic acid. 6. Inter-individual differences in oxidative O-demethylation of the drug are discussed in relation to current theories on the aetiology of schizophrenia and reported fatalities arising from abuse of the drug.

The metabolism of [14C]-debrisoquine in man

1 The synthesis of [14C]-debrisoquine hydrochloride and 4-hydroxy-debrisoquine sulphate is described. 2 The metabolic fate and excretion profile in both urine and faeces of 14C-labelled debrisoquine was studied in five healthy human subjects. 3 Investigations showed that the drug is well-absorbed after a single oral dose of 32 mg and quantitatively eliminated from the body within three days. 4 4-Hydroxy-debrisoquine is the major metabolite of debrisoquine, although significant amounts of 5-,6-, 7- and 8-hydroxy-debrisoquine are also formed. 5 Electron-capture gas chromatography is a useful method for measuring debrisoquine and its five hydroxylated metabolites in urine at the pg level.

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

1. Debrisoquine hydroxylation exhibited profound variation in 72 Egyptian volunteers. 2. The frequency distribution histogram of the metabolic ratio (ratio unchanged drug: 4-hydroxy metabolite in 0-8 h urine) was polymodal. 3. From family data it was possible to define more clearly than before the heterozygous characteristics. 4. Egyptians appear in general to be more extensive oxidizers of debrisoquine than do English subjects. 5. Ramadan fasting was found to lower the absorption of debrisoquine.

Polymorphism of carbon oxidation of drugs and clinical implications

Eight volunteers previously phenotyped for their ability to hydroxylate debrisoquine (four extensive metabolisers (EM), four poor metabolisers (PM) were investigated for their metabolic handling of guanoxan and phenacetin. All three drugs are oxidised at carbon centres. Oxidative dealkylation of phenacetin was determined by measuring the rate of formation of paracetamol. The EM subjects excreted mostly metabolites of guanoxan (mean 29% of dose), whereas the PM group excreted large amounts of unchanged drug (48% of dose). The rate of formation of paracetamol was noticeably slower in the PM group, and, when analysed by minimum estimates of apparent first-order rate constants, the difference between the two phenotypes was significant. Thus the hydroxylation defect shown for debrisoquine metabolism carries over to the oxidative metabolism of phenacetin and guanoxan. Some 5% of the population are genetically defective hydroxylators of drugs. Thus methods for evaluating the metabolism of new drugs in respect of usage and side effects need to be revised.

Taurine conjugates as metabolites of arylacetic acids in the ferret

1. The pattern of conjugation in the ferret of 8 arylacetic acids and, for comparison, benzoic acid and 4-nitrobenzoic acid was examined. 2. The arylacetic acids, phenylacetic, 4-chloro- and 4-nitro phenylacetic, alpha-methylphenylacetic (hydratropic), 1- and 2-naphthylacetic and indol-3-ylacetic acids, were excreted in the urine as taurine and glycine conjugates. Diphenylacetic acid did not form an amino acid conjugate and was excreted as a glucuronide. 3. The taurine conjugate was the major metabolite of 4-nitrophenylacetic, alpha-methylphenylacetic, 1- and 2-naphthylacetic and indol-3-ylacetic acids, whereas the glycine conjugate was the major metabolite of phenylacetic and 4-chlorophenylacetic acids. Taurine conjugation did not occur with benzoic and 4-nitrobenzoic acids which were excreted as glycine and glucuronic acid conjugates. 4. Phenacetylglutamine and 4-hydroxyphenylacetic acid were minor urinary metabolites of phenylacetic in the ferret. 5. A number of taurine conjugates of aliphatic and aromatic acids were synthesized and their characterization and properties were studied. The role of taurine as an alternative to glycine in the metabolic conjugation of arylacetic acids is discussed.

Polymorphic hydroxylation of Debrisoquine in man

Debrisoquine and its primary metabolite, 4-hydroxydebrisoquine, were measured in the urine of 94 volunteers after a single oral dose of 10 mg debrisoquine. The ratio between excreted debrisoquine and its metabolite was bimorphically distributed in the study population. Family studies supported the view that alicyclic 4-hydroxylation of debrisoquine is controlled by a single autosomal gene and that a defect in this metabolic step is caused by a recessive allele.