Antiepileptic drugs and oral contraceptives

ABSTRACT

The present work was conducted to investigate the effect of some of the popular antiepileptic drugs on the efficacy of oral contraceptive pins containing D-norgestrel 0.15 mg and ethinyl oestradiol 0.03 mg in adult female non-pregnant rats. Oral treatment started while the animals were in the oestrus stage of their cycle. Drugs were administered orally for twelve successive days. Half the animals in each group was isolated and the other half was kept with males during the period of treatment. The oral contraceptive used caused a significant increase in both estrogen and progesterone levels compared to the control group. No pregnancies occurred in female rats kept with males during the period of treatment in this group. The simultaneous administration of the oral contraceptive with clonazepam [12.5 mg/kg/day] caused insignificant change in the level of estrogen and progesterone compared to the contraceptive group. No pregnancies occurred in this group. While the concurrent administration of the oral contraceptive with sodium valproate [150 mg/kg/day] resulted in a significant decrease in the levels of both estrogen and progesterone compared to the contraceptive group and insignificant change compared to the control group. Seventy percent of the female rats kept with males in this group became pregnant. On the other hand, the combination of this oral contraceptive with sulthiame [50 mg/kg/day] caused no change in the level of estrogen while progesterone level was significantly decreased compared to the contraceptive group reaching a level nearly that of the control group. No pregnancies occurred in this group. In conclusion we would emphasize that sodium valproate caused failure of the oral contraceptive used in this study. The same cannot necessarily be assumed for other contraceptive drugs. Even though we feel that patients under antiepileptic drugs should be advised as a precaution to use other contraceptive methods in addition to the oral contraceptives