Pharmacokinetics of oxaprozin in women receiving conjugated estrogen

Abstract

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.

An investigation into the effect of tenidap sodium on the pharmacokinetics of a combined oral contraceptive.

“…Plasma samples were obtained on days 10 and 11 of tenidap or placebo treatment in cycles 1 and 2 at 0 (pre-dose), 0.5, 1, 1.5, 2, 3, 4, 6, 8, 10, 14, 24 and 36 h after dosing with the oral contraceptive. On each occasion, a 6 ml blood sample was collected in a heparinised tube, centrifuged and the separated plasma frozen at -20°C.…”

“…These include aspirin [9], oxaprozin [10] and diflunisal [11]. It is therefore important that the effect of tenidap on the pharmacokinetics of a typical combined oral contraceptive (Microgynon 30® (150 ,ug levonorgestrel plus 30 jg ethinyloestradiol)) is studied to assess any potential change in contraceptive efficacy.…”