Limited usefulness of the breath test in evaluation of drug metabolism: a study in human oral contraceptive users treated with dimethylaminoantipyrine and diazepam.

Demethylation of 14C-dimethyl-N-aminoantipyrine (aminopyrine) and 14C-diazepam was measured by means of a breath test in women taking oral contraceptive steroids (OCS) and in controls not receiving OCS. Short-term half-life of 14CO2 in the breath after intake of 2 muCi of aminopyrine was significantly prolonged in women taking OCS when compared with controls. After intake of 2 muCi diazepam there were no statistically significant differences between the two groups. With 2 muCi diazepam or 10 muCi aminopyrine a biexponential decline of 14CO2 content in the breath was superimposed on a circadian, rhythm. 14CO2 in the aminopyrine breath test in the morning increased after the patients had risen from bed, whereas in the diazepam breath test the 14CO2 content decreased. It is concluded that the effect of OCS on drug metabolism is very specific. Furthermore, the appearance of 14CO2 in the breath does not depend only on hepatic microsomal demethylation.