Interação entre Cimetidina e Pentoxifilina

…apparently through an effect on certain microsomal enzyme systems, has been reported to reduce the hepatic metabolism of warfarin-type anticoagulants, phenytoin, propranolol, nifedipine, chlordiazepoxide, diazepam, certain tricyclic antidepressants, lidocaine, theophylline, and metronidazole, thereby delaying elimination and increasing blood levels of these drugs.

However, a crossover study in healthy subjects receiving either 300 mg 4 times daily or 800 mg at bedtime of cimetidine tablets concomitantly with a 300 mg twice-daily dose of theophylline extended-release tablets demonstrated less alteration in steady-state theophylline peak serum levels with the 800 mg at bedtime regimen, particularly in subjects aged 54 years…

(Note: All patients receiving theophylline should be monitored appropriately, regardless of concomitant drug therapy.) Dosage of the drugs mentioned above and other similarly metabolized drugs, particularly those of low therapeutic ratio or in patients with renal and/or hepatic impairment, may require adjustment when starting or stopping the concomitant administration…

Interaction with phenytoin, lidocaine, and theophylline has also been reported to produce adverse clinical effects.

Concomitant administration with cimetidine is reported to increase the average steady state plasma concentration of pentoxifylline (~25%) and the Metabolite I (~30%).

Concomitant administration of strong CYP1A2 inhibitors (including e.g., ciprofloxacin or fluvoxamine) may increase the exposure to pentoxifylline (see ADVERSE REACTIONS).