Placental transfer of ritonavir with zidovudine in the ex vivo placental perfusion model

OBJECTIVE: The object was to determine the placental transfer of ritonavir alone and in combination with zidovudine. STUDY DESIGN: Twelve placental perfusion studies were performed at trough (1-2 mu g/mL) and peak (similar to 20 mu g/mL) combinations of ritonavir and zidovudine. Accumulation of ritonavir was determined. RESULTS: Transfer of ritonavir at trough concentrations was undetectable (<0.025 mu g/mL). The clearance index of ritonavir at peak concentration was 0.085 +/- 0.05 and was unaffected by zidovudine. The fetal concentration of ritonavir was 0.0758 +/- 0.22 mu g/mL at a maternal concentration of similar to 20 mu g/mL and 25.5 +/- 6.9 mu g/mL at a concentration of 100 mu g/mL. There was no tissue accumulation of ritonavir either alone or with zidovudine. CONCLUSION: The clearance index of ritonavir at therapeutic levels was extremely low, with little accumulation in the fetal compartment and no accumulation in placental tissue. Zidovudine does not significantly affect the transfer or accumulation of ritonavir.