Pharmacokinetics of oxaprozin in women receiving conjugated estrogen

The kinetics of a single 1200 mg oral dose of oxaprozin, a nonsteroidal antiinflammatory agent of the propionic acid class, was studied in 22 healthy female volunteers aged 21 to 64 years. Eleven subjects had been taking a conjugated estrogen preparation for at least 3 months; the other 11 subjects served as control women who were not taking conjugated estrogens. Mean pharmacokinetic variables in control and conjugated estrogen groups were: volume of distribution, 15.1 vs 14.1 l; elimination half-life, 59.8 vs 54.2 h; clearance, 3.2 vs 3.1 ml/min; peak plasma concentration, 84.8 vs 90.7 micrograms/ml, respectively. None of the differences were significant. However, the time of peak concentration (8.9 vs 4.0 h) was significantly longer in the control group than in the conjugated estrogen group, respectively (p less than 0.05). Oxaprozin clearance, accomplished by a combination of oxidation and conjugation, is unimpaired by coadministration of conjugated estrogens.