ACUTE DECREASE IN HIV-1 VIRAL LOAD AFTER INITIATION OF ZIDOVUDINE THERAPY - IMPLICATIONS FOR INTERRUPTING VERTICAL TRANSMISSION

Use of zidovudine (AZT) in pregnant women has recently been reported t o reduce the rate of vertical transmission of human immunodeficiency v irus type 1 (HIV-1) possibly through a reduction in maternal viral loa d. To determine how quickly AZT is able to reduce viral load, infectio us virus and plasma HIV-1 RNA were sequentially measured in an HIV-1-i nfected patient at short intervals (hours) after initiation of oral AZ T. Peripheral blood samples were collected at baseline, 1, 2, 4, 8, 12 , 24, 48 hours, and 1 week after initiation of AZT therapy (500 mg/day ) for quantitative plasma HIV-1 RNA levels, p24 antigen levels, and AZ T levels. Quantitative HIV-1 peripheral blood mononuclear cell and pla sma cultures, CD4 cell counts, and MT-2 cell assays for syncytium-indu cing phenotype were performed at baseline, 1, 2 days, and 1 week after initiation of AZT therapy. A significant drop in viral load did not o ccur until after 24-48 hours. AZT should probably be administered at l east 2 days prior to anticipated delivery, if a reduced maternal viral load is responsible for AZT's efficacy in preventing vertical transmi ssion.