Cocaine- and cocaethylene-creatinine clearance ratios in humans.

Cocaine (COC)- and cocaethylene (CE)-creatinine clearance ratios (CCR) were determined in five patients. In each case, COC:CCR greatly exceeded CE:CCR, and in four patients the data suggested renal tubular secretion of COC. For all patients, some renal tubular reabsorption of CE was apparent. These findings may be due, at least in part, to the greater hydrophobicity of CE relative to COC and to the lower pKb of CE (8.23) than that of COC (8.60). The pKb of CE was determined by titrimetry and is reported here for the first time. These data may be useful in investigating the pharmacokinetic profiles of COC and CE in humans and may also help to explain the longer plasma half-life of CE relative to that of COC.