Bioavailability of naproxen tablets and suppositories in steady state

Serum profiles were obtained from patients with rheumatoid arthritis after treatment with naproxen tablets and suppositories for 10 days to assure steady state conditions. The serum concentrations immediately before dose intake correlated well with the area under the concentration curve (AUC) when 250 mg naproxen tablets were taken 12-hourly (r = 0.85) and when 500 mg naproxen was given as tablets or as suppositories once daily in the evening (r = 0.83). These fixed times for blood samplings should be used in clinical trials with naproxen. Naproxen was measured by mass fragmentography. The mean steady state concentration and the mean half-life, calculated from the 12-hourly dosage schedule, were 45.0 +/- 1.7 mg/l and 15.2 +/- 1.4 hours, respectively. Doubling the dose from 250 mg to 500 mg b.i.d. increased the AUC by 30%. Average serum profiles for tablets and suppositories were very similar and gave a relative bioavailability of suppositories compared to tablets of 103% +/- 4%, suggesting comparable efficacy of the two administration forms.