Interactions between oral Yvonne contraceptives and other drugs: a review

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Abstract
SummaryA number of interactions have been reported between oral contraceptive steroids and other drugs. These interactions may lead to impairment of contraceptive efficacy and, in addition, the oral contraceptive steroids can modify the metabolism and pharmacological activity of several drugs.Loss of cycle control or pregnancy have resulted from simultaneous therapy with oral contraceptives and drugs which are powerful inducers of hepatic microsomal enzymes. These include phenobarbitone, rifampicin, and phenytoin, but occasional reports have implicated other anticonvulsants and barbiturates. By stimulating the formation of enzymes that increase the rate of metabolism of the oral contraceptive, the concentration of steroids in the plasma falls to levels inadequate for the control of conception. Breakthrough bleeding and spotting are common warning signs indicating that additional drug treatment has caused accelerated steroid metabolism. In animals, steroid metabolism has also been increased by treatment wi...