Evaluation of prescribing practices - Risk of lactic acidosis with metformin therapy

Background: The risk of lactic acidosis during metformin therapy is linked to specific and well-documented conditions that constitute contraindications or precautions to use of the agent. We conducted a retrospective evaluation of metformin use to determine whether prescribing practices are in accord with published contraindications and precautions. Methods: All patients admitted to the hospital during a 6-month period who received at least 1 dose of metformin were identified through hospital pharmacy records. Patient demographics and clinical characteristics were then evaluated to deter-mine whether metformin was prescribed to patients possessing any of the risk factors associated with development of lactic acidosis. Results: We identified 263 hospitalizations involving 204 patients who received at least 1 dose of metformin during inpatient admission. Patients had at least 1 absolute contraindication to metformin therapy in 71 admissions (27%). In 29 (41%) of these 71 admissions, treatment with metformin continued despite the contraindication. The most common contraindication, elevated serum creatinine concentration, was present or developed during 32 admissions (12%) however, metformin use was appropriately discontinued in only 8 (25%) of these 32 patients. Of the precautions against metformin use, concomitant administration of cationic agents was the most common, occurring in 97 admissions (37%). Conclusions: Many patients are treated with metformin despite having clinical conditions that place them at risk for developing lactic acidosis. To minimize this risk, it is essential that prescribers develop a better understanding of the prescribing guidelines for metformin.