The effect of acyclovir on creatinine transport across human renal proximal tubular cell (HK-2) monolayers. The transport (basolateral-to-apical) of creatinine was assessed in HK-2 cells monolayers. Cell monolayers were exposed to [2-14C] creatinine (5 μM) in the presence or absence of quinidine (1E+03 μM), cimetidine (1E+03 μM) or acyclovir (22 to 89 μM) for 30 minutes. The transport of creatinine was assessed by measuring the appearance of [2-14C] creatinine radioactivity in the apical compartment at specific time intervals (0, 7.5, 15, 22.5 and 30 minutes) for 30 minutes. Radioactivity was measured as disintegrations per minute (DPM). Creatinine transport is expressed as the concentration of [2-14C] creatinine in the apical compartment. Results are presented as the mean (±standard error (SE)) from 3 cell monolayer experiments. * p < 0.05, compared to [2-14C] creatinine radioactivity in the apical compartment in the absence of quinidine, cimetidine or acyclovir.