trimpex and Fortamet Interactions

Interactions between trimpex(trimethoprim) and Fortamet (metformin)

trimethoprim and metformin (Moderate Drug-Drug)

MONITOR: Trimethoprim is a cationic drug and theoretically could decrease the excretion of metformin by competing for renal tubular transport. Although this interaction has not been specifically reported for trimethoprim, cimetidine (also a cationic drug) has been reported to interact with metformin in this manner. Increased metformin levels may increase the risk of lactic acidosis.

MANAGEMENT: If trimethoprim and metformin must be used together, particularly slow and cautious titration of metformin dosage is recommended. The maximal dose of metformin probably also should be reduced until further information about this interaction is available. Patients should be advised to monitor their blood glucose and to promptly notify their physician if they experience possible signs of lactic acidosis such as malaise, myalgia, respiratory distress, hyperventilation, slow or irregular heartbeat, somnolence, abdominal upset, or other unusual symptoms.