Acetylator phenotyping with sulphadimidine in patients receiving isoniazid

The possible competition of isoniazid for the acetylation of sulphadimidine was studied by comparing the degree of acetylation of urine sulphadimidine (1 g orally) in isoniazid-treated and in isoniazid-untreated patients. The former group (isoniazid 300 mg once daily) consisted of 5 slow and 5 rapid acetylators and the latter group of 5 and 6 respective acetylator phenotypes. In all of the 4-8, 8-12 and 12-24 h urine fractions, the acetylation percentage of sulphadimidine and its distribution pattern were practically unaffected by the isoniazid. This suggests that isoniazid therapy does not interfere significantly with the routine acetylator phenotyping by means of sulphadimidine.