Other side effects include irregular heartbeat, impotence, rash, visual changes, allergic reactions, and hepatitis. Gastrointestinal Diarrhea usually mild has been reported in approximately in 100 patients. Beta-blockers except atenolol, betaxolol, bisoprolol, nadolol, penbutolol effects may be use renally-eliminated beta-blocker or alternative H2 antagonist. Because of inhibition of warfarin metabolism, cimetidine may increase INR in patients on anticoagulation therapy. An elderly, terminally ill dehydrated patient with organic brain syndrome receiving concomitant antipsychotic agents and Tagamet 4800 mg intravenously over 24-hour period experienced mental deterioration with reversal on Tagamet discontinuation. Dosing The dosage your healthcare provider recommends will vary depending on number of factors, including: The medical condition being treated Your age Other medical conditions you may have Other cimetidine ostaa verkosta medications you may be taking.