myotoxic

Myotoxic describes any substance or condition capable of damaging skeletal muscle tissue. In toxicology and pharmacology, myotoxic agents include certain animal venoms, environmental toxins, and drugs whose adverse effects include myopathy or rhabdomyolysis. The term distinguishes toxins with direct effects on muscle fibers from those that primarily affect nerves or other tissues.

Mechanisms of myotoxicity include disruption of muscle cell membranes by enzymes such as phospholipases A2 found in many snake venoms; disruption of calcium homeostasis; mitochondrial dysfunction; and oxidative stress. These processes can lead to muscle fiber necrosis and leakage of intracellular enzymes into the bloodstream.

Common sources of myotoxicity include snake venoms that contain myotoxins, some bacterial toxins, and certain drugs known for myotoxic potential. Notable drug-associated myotoxicity involves statins and the antibiotic daptomycin; other drugs may contribute when used with interacting substances or in overdose. Environmental exposures, such as alcohol or heavy metals, can also produce myotoxic effects.

Clinical features typically include muscle pain and weakness, possible swelling, and dark urine due to myoglobin in more severe cases. Laboratory findings often show elevated serum creatine kinase and may include myoglobinuria. Diagnosis relies on history, physical findings, and laboratory data; further testing like electromyography or imaging may be used in unclear cases.

Treatment focuses on addressing the underlying cause: antivenom for venom-induced myotoxicity, aggressive intravenous hydration to prevent renal injury in rhabdomyolysis, and cessation or substitution of the offending drug. Supportive care and monitoring are important, and prognosis varies with the toxin and extent of muscle damage.

See also: myopathy, rhabdomyolysis, pharmacovigilance.