Effect of zidovudine on perinatal HIV-1 transmission and maternal viral load

Shaffer et al. reported that in a randomized placebo-controlled trial in Thailand a short course of antenatal zidovudine administered from 36 weeks gestation until delivery reduced perinatal HIV-1 transmission by 50%. However while this course reduced perinatal HIV-1 transmission by 50% and the level of presumed intrapartum transmission by 61% in-utero transmission was reduced by only 29%. The overall reduction in transmission in the Pediatric AIDS Clinical Trials Group (PACTG) protocol 076 was 68% with similarly significant presumed reductions in intrapartum and in-utero HIV transmission. Shaffer et al. reported a greater net reduction in plasma HIV-1 RNA load from entry to delivery compared with PACTG 076. The authors found no clear evidence of a larger early decrease in RNA on the basis of an analysis of median change in plasma HIV RNA loads according to quartile of treatment duration. Finally the 2 studies differed in the estimated proportion of zidovudine treatment effect (PTE) explained by maternal plasma HIV-1 RNA load at delivery which was 80% in the Thai study and 11% in PACTG 076. Insufficient data were available with which to calculate PTE according to treatment duration. The full PACTG 076 zidovudine regimen should continue to be recommended for prophylaxis of perinatal HIV-1 transmission in countries capable of implementing it.