Prescription-medication sharing among family members: an unrecognized cause of a serious drug adverse event in a patient with impaired renal function

Many medications need to be avoided in chronic kidney disease (CKD) because of increased toxicity. Metformin - an oral hypoglycemic drug universally recommended as the first-line treatment for type 2 diabetes mellitus (T2DM) - undergoes significant accumulation in advanced CKD that may ultimately lead to lactic acidosis. Recently, it has been found that side effects of the therapy may occasionally neither be linked to improper prescription nor lack of dose adjustment by the physician, but can result from borrowing and sharing of drugs with relatives and friends. This poorly recognized problem has never been studied in renal patients. This work contains a discussion on the diagnostic problems associated with proper diagnosis of the etiology of severe acidosis in an elderly woman with advanced CKD and diabetes. The patient developed severe lactic acidosis by taking metformin that was prescribed by another doctor to her son, who was also diabetic. The diagnosis of lactic acidosis was delayed since the initial laboratory assessments had focused mostly on dehydration and substance abuse.