Effect of allopurinol on caffeine disposition in man.

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.

The pharmacokinetics of caffeine and its dimethylxanthine metabolites in patients with chronic liver disease.

“…However, the median caffeine clearance was higher in the smokers and this may have biased the results in the compensated group. Similarly, many of the patients were taking drugs, such as cimetidine and allopurinol which might have affected oxidation rates (Roberts et al, 1981;Grant et al, 1986). Where possible all medication was stopped 48 h before the study but the effects of the drugs on the oxidation rate might have persisted, at least to a degree, in the patients with decompensated disease.…”

Phenotyping of N-acetyltransferase type 2 and xanthine oxidase with caffeine: when should urine samples be collected?

“…For the assessment of XO activity, the ratios 1U/1X and (1U)/(1X+1U) have been used and validated in combination with NAT2 and CYP1A2 assessments [17][18][19][20][21] and in the framework of cocktail phenotyping studies [22][23][24]. No direct comparison between the performance of the two ratios has been published and for both, some validation issues have not yet been addressed.…”

Growth Hormone Does Not Alter CYP2A6 Activity in Growth Hormone‐Deficient Children

“…Caffeine metabolites were determined according to the high-pressure liquid chromatography method described by Grant et al [23]. Caffeine and their metabolites were separated by a Waters Novapak C18 reverse-phase column (4 µ m particle size, 25 cm × 4.6 mm internal diameter) (Millipore Ibérica S.A., Madrid, Spain), which was eluted isocratically with a mobile phase containing acetic acid/methanol/water (0.5:90:905.5 vol/ vol/vol) at a flow rate of 1 ml/min.…”