Drug-induced myopathy

**Definition:** Myopathy caused by drugs that ranges from mild myalgias with or without mild weakness to chronic myopathy with severe weakness, to massive rhabdomyolysis with acute renal failure. It could be due to several different mechanisms including direct myotoxicity, immune mediated and indirect muscle damage through drug-induced coma, drug-induced hypokalaemia, drug-induced hyperkinetic states or dystonic states.

**Long definition:** Drug-induced myopathy is myotoxicity caused by the use of drugs resulting in muscle injury. Two forms of drug-induced myopathy are particularly well known. The first is myopathy due to lipid-lowering agents including fibric acid derivatives, HMG-CoA reductase inhibitors (statins), and niacin (nicotinic acid). Reactions include any combination of muscle aches, cramping, tenderness, or weakness. Indications of toxicity are elevated serum creatinine kinase, myalgia, exercise-induced pain, rhabdomyolysis, and myoglobinuria. The second type is glucocorticoid myopathy that occurs with chronic administration, or as acute quadriplegic myopathy secondary to high-dose IV glucocorticoid use, producing weakness of the proximal muscles and neck flexors. (