Do anticonvulsants reduce the efficacy of oral contraceptives?
ABSTRACT Women in our area with epilepsy who were also taking oral contraceptives were identified. Of 82 patients taking oral contraceptives, 41 had used both anticonvulsants and oral contraceptives for a total of 955 months. Three documented oral contraceptive (pill) failures occurred during this period, whereas the expected number of 0.12 (relative risk, 25; 95% confience interval, 5 to 73). No pill failures were observed in 2,278 months among women with epilepsy who were taking oral contraceptives but who were not taking anticonvulsants at this time. Thus our data support the suggestion that there is an increased rate of pill failure among women taking anticonvulsants. In view of this diminished effectiveness, the advisability of using oral contraceptives rather than one of the other forms of contraception when anticonvulsant medication is being used concurrently may need to be reevaluated.
- SourceAvailable from: Michael Orme[Show abstract] [Hide abstract]
ABSTRACT: 1. We have searched the adverse reactions register for the years 1968-84 in an attempt to evaluate data relating to reported pregnancies in women on oral contraceptive steroids (OCS) who concurrently received either an antiepileptic drug or an antibiotic. 2. A total of 43 pregnancies were reported in women on OC therapy who concurrently received antiepileptic drugs and 63 pregnancies in women receiving antibiotics. In addition the number of prescriptions for both antiepileptics and antibiotics in England are reported for the years 1973-84.British Journal of Clinical Pharmacology 06/1988; 25(5):527-32. DOI:10.1111/j.1365-2125.1988.tb03341.x · 3.69 Impact Factor
Article: [Drug interactions with phenytoin].[Show abstract] [Hide abstract]
ABSTRACT: Drug interactions with phenytoin are a frequent occurrence, although their clinical relevance has often been overemphasised. Probably the most important of such interactions are those resulting in inhibition of phenytoin metabolism: due to the saturable nature of phenytoin biotransformation even minor degrees of inhibition can produce disproportionate changes in both steady-state serum concentration and the magnitude of pharmacological effect. Phenytoin has marked enzyme-inducing properties and can stimulate the metabolism of many concurrently administered drugs, thereby reducing their therapeutic efficacy. Clinically important examples of such interactions include a reduction of the anticoagulant effect of dicoumarol, a decrease in the prophylactic efficacy of the contraceptive pill and failure of response to various corticosteroid agents when administered therapeutically or diagnostically. Unless complicated by additional mechanisms, plasma protein binding interactions with phenytoin are seldom of clinical significance. However, they may alter considerably the relationship between serum drug concentration and clinical response, a possibility which needs to be taken into account when interpreting serum phenytoin levels in clinical practice.Medizinische Monatsschrift für Pharmazeuten 08/1980; 3(7):206-9.
- Journal of Obstetrics and Gynaecology 10/1980; 1(2):126-138. DOI:10.3109/01443618009067363 · 0.60 Impact Factor