Etintidine-theophylline interaction study in humans

Etintidine HCl is a potent H2‐blocker. The effect of clinical doses of etintidine on the disposition of theophylline was investigated in 10 male volunteers. This was a double‐blind, two‐way crossover study. Each subject received etintidine (400 mg) or placebo twice a day with meals for 4 days on two occasions (separated by 4 days). On each occasion, the subjects were fasted overnight on Day 3 and were given an oral dose of theophylline elixir (5 mg/kg) 30 min following the administration of the morning dose of etintidine or placebo on Day 4. Blood samples were collected prior to and up to 24 h following the administration of theophylline. Plasma theophylline levels were analysed by HPLC. Theophylline was rapidly absorbed following oral administration of the theophylline elixir to both the placebo and etintidine treatment groups. Comparison of the pharmacokinetic parameters of theophylline between the etintidine and the placebo groups indicates that while etintidine did not significantly (p > 0.05) affect the apparent Cmax (11.1 vs 10.0 μg ml−1) and Tmax (1.7 vs 1.4 h) values of theophylline, etintidine significantly reduced the oral clearance (0.0200 vs 0.0564 1kg−1 h−1, p = 0.000006) and prolonged the elimination half‐life (16.8 vs 6.0 h) of theophylline. The data indicate that etintidine, like cimetidine, extended the elimination of theophylline in humans.