Uptake of teicoplanin by isolated rat hepatocytes: Comparison with in vivo hepatic distribution

Tissue distribution of teicoplanin, a large glycopeptide antibiotic, is slow but at equilibrium its whole body distribution volume is relatively large (Vss = 1.18-2.78 liter/kg), despite a high binding to plasma albumin. In vivo distribution into liver is extensive. Previous in vitro homogenate studies suggest that teicoplanin binds to cell membranes but only enters some cells. This possibility was investigated with isolated hepatocytes incubated for 4 h with [C-14] teicoplanin alone and in the presence of additional teicoplanin (1 and 100 mug/ml). Uptake was determined after separating the cells by rapid centrifugation through a dibutyl phthalate layer and assessing viability by the trypan blue exclusion test. Teicoplanin cell uptake curves, initially rapid followed by slower distribution (which agrees with in vivo findings), were adequately described by a closed two-compartment model. Whereas entry into hepatocytes was independent of drug concentration, binding to the cell exterior membrane was concentration-dependent. The equilibrium distribution ratio (Kpu(c) +/- S.D.; 42 +/- 10) was somewhat smaller than estimated in vivo (106 +/- 9), but similar to that reported previously in vitro using liver homogenates (54 +/- 11). Also, the estimated membrane permeability-surface area product was larger in vitro than in vivo (PSu +/- S.D.; 5.5 +/- 2.9 versus 0.74 +/- 0.10 ml/min per whole liver). The most likely explanation for this difference is that in vivo only a small fraction of the total cell surface area is exposed to the perisinusoidal space, where exchange occurs.