The effects of cimetidine, ranitidine and famotidine on the single-dose pharmacokinetics of naproxen and its metabolites in humans.

We studied the effects of cimetidine, ranitidine and famotidine on the kinetics of naproxen. The mean t1/2 beta of naproxen in 6 subjects was 25.7 +/- 5.4 h (range 16 to 36). Naproxen acyl glucuronide accounts for 50.9 +/- 6.9% of the dose, its isomerized isoglucuronide for 6.8 +/- 2.6%, O-desmethylnaproxen acyl glucuronide for 14.3 +/- 4.1% and its isoglucuronide for 5.5 +/- 1.5% (n = 6). Naproxen (1.3 +/- 1.1%) and O-desmethylnaproxen (0.6 +/- 0.4%) are excreted in negligible amounts. Cimetidine, ranitidine and famotidine all reduced significantly the t1/2 beta of naproxen by 50% from 25 h to 13 h and the t1/2 alpha from 4.0 h to 1.1 h. No effect of the H2 antagonists was observed on the absorption of naproxen. They also reduced the Vss of naproxen by 50%. The amount of naproxen acyl glucuronide, naproxen isoglucuronide and O-desmethylnaproxen acyl glucuronide excreted in the urine, remained unchanged, 60%, 7%, and 14% respectively.