H2 receptor antagonist.

Indications: benign gastric and duodenal ulceration, stomach ulcer, reflux oesophagitis, Zollinger - Ellison syndrome, other conditions where gastric and acid reduction is beneficial.

Cautions: Should be used with caution in impaired renal function, hepatic impairment; in pregnancy and breast- feeding, they may mask symptoms of gastric cancer.

Side effect: Diarrhea and other gastro-intestinal disturbances, dizziness, rash, tiredness; occasionally, gynaecomastia (in high doses), reversible confusional states, reversible liver damage, headache; rarely, decreased blood counts, alopecia, muscle or joint pain, bradycardia; interstitial nephritis and acute pancreatitis.

Drug Interactions: Increases plasma concentration of cyclosporine, diltiazem, labtalol, metronidazole, niphedipine, propranolol, procainamide and quinidine. It also potentiates the effects of warfarin, theophyline, carbamazepine, phenytoin, chlormethiazole, amitriptyline, desiperamine, imipramine, clonazepam, chlordiazepoxide, diazepam, flurazepam and nitrazepam.Cimetidine increases the cardiac risks associated with lidocaine and decreases absorption of ketokinazole.Rifampicin reduces plasma concentration of cimetidine and absorption of cimetidine may be decreased in the presence of antacids and sucralfate.

Dose: 400 mg twice daily (with breakfast and at night) or 800 mg at night (benign gastric and duodenal ulceration) for at least 4 weeks (6 weeks in gastric ulceration, 8 weeks in NSAID-associated ulceration); when necessary the dose may be increased to 400 mg 4 times daily; INFANT under 1 year 20 mg/kg daily in divided doses has been used; CHILD 1–12 years, 25– 30 mg/kg daily in divided doses; max. 400 mg 4 times daily Maintenance, 400 mg at night or 400mg morning and night. Reflux oesophagitis, 400mg 4 times daily for 4–8 weeks.

Prophylaxis of stress ulceration, 200–400mg every 4– 6 hours. Gastric acid reduction (prophylaxis of acid aspiration; do not use syrup), obstetrics 400mg at start of labour, then up to 400 mg every 4 hours if required (max.

2.4 g daily); surgical procedures 400 mg 90–120 minutes before induction of general anaesthesia Short-bowel syndrome, 400mg twice daily (with breakfast and at bedtime) adjusted according to response. To reduce degradation of pancreatic enzyme supplements, 0.8–1.6 g daily in 4 divided doses 1–1½ hours before meals.