Pharmacokinetics and pharmacodynamics of naproxen in acute experimental hepatitis

The pharmacokinetics of intravenous naproxen (CAS 22204-53-1) 6 mg kg-1, were studied in Wistar rats under control conditions and 1, 3 and 10 days after the induction of acute hepatitis by a single intraperitoneal injection of galactosamine 375 mg kg-1. In non-intoxicated rats t1/2 was 5.31 +/- 0.90 h, Vd was 0.21 +/- 0.01 l.kg-1, Cl was 17 +/- 5 ml.h-1.kg-1, AUC was 354.4 +/- 8.8 micrograms.h.ml-1 and 99.18 +/- 0.09% of naproxen was bound to plasma proteins. One day after intoxication the liver was considerably damaged; cytochrome P450, the main enzymatic system for naproxen metabolism, was decreased in 90%. Naproxen t1/2 was increased to 11.9 +/- 1.2 h but Vd did not change significantly, therefore clearance was reduced to 37%. Binding to plasma proteins was decreased to 83.21 +/- 0.27%. At day 3 liver function and naproxen pharmacokinetics exhibited a partial recovery, t1/2 was 6.59 +/- 0.92 h and clearance was 12.2 +/- 5 ml.h-1.kg-1 being not significantly different from controls; notwithstanding AUC was still significantly different from that of non-intoxicated rats. 10 days after galactosamine injection all pharmacokinetic parameters, as well as those of liver function, returned to basal levels. The results indicate that acute hepatitis produces an important reduction in naproxen elimination. Changes in naproxen disposition, which exhibit a time course similar to that of liver damage, are mainly determined by a decrease in intrinsic hepatic clearance and in the binding to plasma proteins.