Vitamin B6 metabolism in women using oral contraceptives

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Abstract
To study the effect of oral contraceptives on the metabolism of vitamin B6, three women who use these drugs ("users") and two who do not use them ("nonusers") were fed a constant diet containing 1.9 mg vitamin B6 for 11 days. The users not only excreted elevated amounts of kynurenine-pathway metabolites in response to 2 g l-tryptophan but also excreted approximately 30% less urinary vitamin B6 than the nonusers. Blood vitamin B6 was only slightly lower in the users. Both groups excreted similar amounts of 4-pyridoxic acid. Results obtained from giving the tryptophan load test at different times of the day and when the users had discontinued taking the contraceptive for the menses interval emphasize the importance of giving this test dose at the same time of day and during the time the women are taking the drug.