HIV mother-to-child transmission (MTCT) is significantly reduced if antepartum viral load (apVL) is<50 copies/mL. Pharmacokinetic studies suggest increasing the dosage of lopinavir/ritonavir (LPV/r) in pregnancy. It is important to assess tolerance, safety, and rate of patients presenting a apVL<50 copies/mL when treating with increased dose of LPV/r during pregnancy. Confirmed HIV-infected pregnant women with a fetus at a gestational age of 14-33 weeks were randomly assigned to receive LPV/r 400/100 or 600/150 mg b.i.d. plus two nucleoside analogues (NRTIs). Treatment was discontinued in the case of alanine transaminase (ALT) of grade III elevation or higher, glucose, or triglycerides. Thirty-two women were randomized to the LPV/r 400/100 mg dose, and 31 women were randomized to the 600/150 mg dose. Overall, 9.4% of the women receiving the conventional dose, and 17.2% receiving the increased dose, discontinued treatment because of adverse events (p=0.29). The rates of gastrointestinal (GI) symptoms, laboratory abnormalities, preterm delivery, and low birth weight were similar in both groups. There were no cases of HIV MTCT. Among the women with a baseline VL>50 copies/mL assigned to the conventional dose group, 45% (95% confidence interval [CI] 62.5-27.5%) had a apVL>50 copies/mL compared with 10.5% (95% CI 21.6-0.6%) of those assigned to the increased dose group (p=0.01). There was no significant difference found for the patients with a baseline VL<50 copies/mL. In pregnant women with a baseline VL>50 copies/mL, it may be warranted to initiate LPV/r dosing at 600/150 mg, whereas the conventional dose is sufficient for pregnant women with a baseline VL<50 copies/mL.