Oxaprozin pharmacokinetics in patients with congestive heart failure.

12 patients aged 26-71 years with stable, compensated congestive heart failure (CHF) and 12 healthy controls matched for age, sex, height, weight, and serum albumin, received a 1200-mg oral dose of the nonsteroidal antiinflammatory agent 4,5-diphenyl-2-oxazolepropionic acid (oxaprozin). Serum oxaprozin levels were measured by high pressure liquid chromatography during the next 14 days. Oxaprozin elimination half-life was not different between controls and CHF patients (63 vs 69 h), but peak serum levels were lower (79 vs 63 micrograms/ml, p less than 0.01), apparent volume of distribution was larger (0.22 vs 0.29 l/kg, p less than 0.05) and clearance tended to be higher, although not significantly so, (0.042 vs 0.053 ml/min/kg) in CHF patients. These differences might have been due to reduced serum protein binding (increased free fraction) in CHF patients (0.25 vs 0.44% unbound, p less than 0.1). After correction for individual values of free fraction, groups did not differ in peak free oxaprozin serum levels (0.20 vs 0.26 micrograms/ml), unbound volume of distribution (92 vs 83 l/kg), or unbound clearance (17.5 vs 15.0 ml/min/kg). Thus protein binding of oxaprozin in the present study was reduced in CHF due either to the underlying disease or to the concurrent medications. This in turn caused reciprocal reduction in total (free plus bound) oxaprozin levels and elevated estimates of volume of distribution and clearance. Although protein binding is altered, CHF causes no significant alteration in distribution of free oxaprozin nor free clearance of oxaprozin, which is accomplished by a combination of oxidation and conjugation.