Urinary metabolites of caffeine in pregnant women.

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Abstract
In a study of caffeine and its metabolites in pregnant and non-pregnant women, on average 56.8% of the administered caffeine dose was recovered in the urine in both groups. However, compared to the controls, the pregnant subjects produced smaller amounts of 1-methylxanthine and 1- methyluric acid, whereas the excretion of most of the other metabolites, particularly 3,7-dimethylxanthine and 3-methylxanthine tended to be greater. It is suggested that hormonal influences on the hepatic caffeine metabolising enzymes might be implicated.