Quiz 70: Drugs for Modifying Conception


Some of the antibiotics such as rifampicin induce the cytochrome p450 enzymes, which increase the metabolism of drugs that undergo metabolism through the liver cytochrome p450 enzymes. Rifampicin is an antibiotic that inhibits the bacterial deoxyribonucleic acid (DNA)-dependent ribonucleic acid (RNA) synthesis by inhibiting DNA-dependent RNA polymerase. The antibiotics interact with oral contraceptives (OCs) in two ways which are as follows: • Antibiotics like rifampicin induce cytochrome p450 enzymes in the liver, which results in increased hepatic hydroxylation of estrogens. • Antibiotics also interrupt with the enterohepatic cycling of estrogens. This is done by reducing the bacterial population of the small intestine. The intestinal bacteria are responsible for hydrolysis of the glucuronide moiety to free drug. Glucuronide moiety is an estrogen metabolite found in bile. Thus, reduces circulating concentrations of ethinylestradiol. The increased metabolism of oral OCs results in decrease of their levels in the plasma. Thus, results in failure of contraceptives.

Clomiphene belongs to the group triphenylethylene and is a selective estrogen receptor modulator (SERM) that is used for ovulation induction to reverse anovulation or oligoovulation. Thus, it is a fertility drug that acts by inhibiting the negative feedback in the hypothalamus. It occupies the estrogen receptors in the hypothalamus and inhibits the binding of estrogen. Thus, it inhibits the negative feedback loop of estrogen. Due to the inhibition of negative feedback loop, the hypothalamus releases gonadotropin releasing hormone (GnRH). The GnRH acts on the anterior pituitary and enhance the secretion of luteinizing hormone (LH) and follicle stimulating hormone (FSH), which promote the process of ovulation.

As "L" had an unprotected sex, she can be prescribed with emergency contraceptives to avoid unwanted pregnancy. Two types of emergency contraceptives are available, which include Plan B and Plan B One Step. Both are available as OTC (over the counter) drug for those above 17 years of age. Plan B works best before 72 hours of intercourse and Plan B One Step works within 120 hours of intercourse.

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