No abstract

A method is presented for the use of caffeine, in the forms commonly ingested by a large proportion of the world's population, to test for the clinically important acetylation polymorphism. Each of 146 subjects provided a spot sample of urine between 2 and 6 h after coffee, tea or cola soft drink consumption, and the molar ratio of 5‐acetylamino‐6‐ formylamino −3‐methyluracil (AFMU) to 1‐methylxanthine (1X) was determined by a simple h.p.l.c. assay. The ratio afforded segregation of three apparent modes of acetylation capacity in this population, in concordance with a standard sulphamethazine phenotyping procedure and with other methods using controlled caffeine intake and urine collections. The day‐to‐day consistency of the method was established in eight selected subjects.

No abstract

Caffeine (5 mg kg-') was administered orally to two healthy, non-smoking subjects on three separate occasions-before, and during therapy with the xanthine oxidase inhibitor allopurinol at doses of either 300 or 600 mg daily. Plasma and urinary levels of methylxanthines, endogenous oxypurines and allopurinol and its metabolite oxypurinol were measured using h.p.l.c. analyses. Allopurinol treatment caused a specific, dose-dependent inhibition of the conversion of the caffeine metabolite 1-methylxanthine (1X) to 1-methyluric acid (1U). A good correlation was observed in both subjects between the urinary 1U/1X molar ratio and the ratio of endogenous urate to hypoxanthine + xanthine at the different allopurinol doses, supporting the proposal that the 1U/lX molar ratio after caffeine intake provides an in vivo index of xanthine oxidase activity in man.

No abstract