An evaluation of the safety of ranitidine during seven years daily oral administration to beagle dogs.

1 Ranitidine hydrochloride was administered orally to Beagles at doses equivalent to 50 mg once daily, or 5 mg twice daily, of ranitidine base/kg for more than 7 years. 2 Apart from looseness of faeces, seen mainly after doses of 50 mg/kg and only rarely after the first year of such treatment, there were no adverse clinical effects. There were no deaths related to treatment. 3 Periodic gastroscopy revealed nothing abnormal. 4 Peak plasma levels of ranitidine occurred within 2 h of dosing; levels were proportional to the doses administered. 5 There were no major differences in fasting plasma gastrin levels between treated and untreated dogs; the expected increase occurred in response to the provision of food and, predictably, this was greater following a dose of ranitidine. 6 A normal histamine-induced gastric secretory response was demonstrated. 7 Necropsy revealed no lesions of toxicological significance. Macroscopically the stomachs appeared normal but microscopic examination showed some gastritis in both treated and control dogs. No changes in enterochromaffin-like (ECL) cells were detected. Electron microscopy showed unimpaired secretory activity of parietal cells. 8 Thus, after more than 7 years administration to beagle dogs of doses in excess of the normal daily therapeutic dose, the stomachs showed no changes attributable to treatment and their secretory capacity was unimpaired.