The role of antiretrovirals and drug resistance in vertical transmission of HIV-1 infection.

Large-cohort studies in North America, Europe, and Thailand have shown that zidovudine/azidothymidine (AZT) monotherapy, given at the late stages of pregnancy, is of proven benefit in reducing mother-to-infant HIV transmission by 51% to 68%. AZT monotherapy will not be of long-term benefit for mothers because no single drug can counteract viral infection; benefits to babies will be short-lived if HIV-1 is acquired through breastfeeding after birth. Unfortunately, ongoing mutation of HIV under conditions of drug pressure allows for the evolution and selection of AZT-resistant viruses. Emergence of AZT-resistant variants in pregnant mothers (7-29%) and their infected offspring (5-21%) has been described in several studies. Drug resistance arises more frequently in those mothers who received AZT therapy before pregnancy. Recent advances in combination chemotherapy may provide alternative strategies in prevention of vertical transmission and drug resistance. Genotypic screening of the HIV-1 isolated from pregnant mothers may provide rational modifications in antiretroviral (ARV) strategies to circumvent vertical HIV transmission. This may be of advantage for resource-rich nations but not for underdeveloped nations with limited access to ARVs. Public health programs are vital to have an impact on the tragic pandemic of pediatric AIDS.