Drug-induced myopathies occur when a drug causes a toxic effect that results in myalgia, muscle damage, and/or muscle breakdown. Most drug-induced myopathies are reversible upon drug discontinuation if recognized early. They commonly include acute mild to severe myalgia and/or muscle weakness, sometimes accompanied by serum creatine kinase (CK) elevations.

More severe drug-induced myopathies can include chronic myopathy, myositis (dermatomyositis, polymyositis), myonecrosis, or rhabdomyolysis with the potential for life-threatening complications of myoglobinuria, hyperkalemia, and acute renal failure.

Other signs and symptoms include muscle soreness, tenderness, swelling, stiffness, spasms, cramps, diminished tendon reflexes, dyspnea, dysphagia, weight loss, oliguria, discolored urine, and/or exercise intolerance. A patient may also present with fatigue and generalized, symmetrical weakness, typically proximal. Pain is not always present. Sometimes patients are asymptomatic.

Statins are a known cause of myopathy, and the risk and severity of muscle toxicity increases with dose. Patients with statin-induced myopathy may present with flu-like symptoms along with muscle complaints. Other associated medications include fibrates (gemfibrozil), corticosteroids (prednisone), cyclosporine, daptomycin, cimetidine, penicillamine, levodopa, interferon-a, gemcitabine, procainamide, laxatives, diuretics, zidovudine, chloroquine, hydroxychloroquine, emetine, vincristine, isotretinoin, colchicine, excessive antacids, antipsychotic drugs, tumor necrosis factor (TNF) inhibitors, heroin, cocaine, and amphetamine. Alcohol can also induce myopathy. Alcohol-induced myopathy typically presents hours after a binge-drinking episode in patients with a history of chronic alcohol use.

Related topics: Immune-mediated necrotizing myopathy, Mitochondrial myopathy, Drug-induced muscle spasm