Elimination of caffeine and metamizole in the menstrual cycle of the fertile female

: The elimination of caffeine from serum and that of the main metabolites of metamizol in serum were investigated in 9 healthy women on days 1, 8, 14 and 21 of the menstrual cycle. In the luteal phase, when the progesterone level is highest and the estradiol concentration is high as well, the elimination of caffeine is about 25% longer than in the follicular phase. In contrast to caffeine, the metabolism of metamizol is slightly accelerated if the endogenous hormone level is high. The present results suggest that endogenous hormones have different effects on biotransformation activities. These results are without practical consequences yet.