Ans. B: Nevirapine Majority of mother to child transmission of HIV-1 occurs during the intrapaum period. Mechanism of veical transmission include infection after rupture of the membranes and direct contact of the fetus with infected secretions of blood from the maternal genital tract. Nevirapine is a non-nucleoside reverse transcriptase inhibitor (NNI) used to treat HIV-1 infection and AIDS. It target the reverse transcriptase enzyme, an essential viral enzyme which transcribes viral RNA into DNA. Nevirapine is not effective against HIV-2, as the pocket of the HIV-2 reverse transcriptase has a different structure, which confers intrinsic resistance to the NNI class. Adverse effects The most common adverse effect of nevirapine is the development of mild or moderate rash (13%). Severe or life-threatening skin reactions have been observed in 1.5% of patients, including Stevens-Johnson syndrome, toxic epidermal necrolysis and hypersensitivity. Drug interactions Significant lowering of nevirapine levels occurs with the anti-tuberculosis drug, rifampicin. Nevirapine is an inducer of cytochrome P450 isoenzymes. It reduces the levels of several co-administered drugs including the antiretrovirals eirenz, indinavir, lopinavir, nelfinavir and saquinavir, as well as clarithromycin, ketoconazole, forms of hormonal contraception, and methadone. Preventing mother-to-child transmission A single dose of nevirapine given to both mother and child reduced the rate of HIV transmission by almost 50% compared with a very sho course of zidovudine (AZT) prophylaxis.(This 50% is the comparative reduction of HIV transmission between the two drugs) Zidovudine administered during pregnancy and labor and to the newborn reduces the risk of veical transmission by 70%. Cesarean section is associated with additional risk reduction compared to vaginal delivery.