In a study completed in 2003, 50 HIV-1 infected, protease inhibitor and lamivudine naïve children age 4 weeks to 2 years received ritonavir 350 or 450 mg/m2 every 12 hours co-administered with zidovudine 160 mg/m2 every 8 hours and lamivudine 4 mg/kg every 12 hours.