Melanotan II Injection Linked to Severe Systemic Toxicity and Muscle Breakdown

Melanotan II is a synthetic peptide analog of alpha-melanocyte-stimulating hormone (α-MSH) often illicitly used for cosmetic tanning due to its action on melanocortin receptors (MC1R, MC3R, MC4R). While known for side effects like nausea and flushing, severe adverse events are less frequently documented in formal literature. This case report highlights a critical gap in understanding the full spectrum of severe systemic toxicities, specifically rhabdomyolysis, associated with unregulated Melanotan II use.

Upon admission, the patient exhibited profound muscle pain, dark urine, and signs of acute kidney injury. Laboratory tests revealed a dramatically elevated creatine kinase (CK) level of >100,000 U/L (normal range <200 U/L), unequivocally indicating severe muscle breakdown. His serum creatinine level was 3.5 mg/dL (normal 0.6-1.2 mg/dL), consistent with significant acute kidney injury. Further analysis showed severe electrolyte imbalances, including hyperkalemia at 6.1 mEq/L (normal 3.5-5.0 mEq/L), and elevated liver enzymes, with AST at 1200 U/L and ALT at 850 U/L, suggesting broader systemic involvement. > The most critical finding was the development of severe rhabdomyolysis leading to acute kidney injury, directly linked to Melanotan II use, requiring intensive medical intervention. The patient's condition necessitated aggressive intravenous fluid resuscitation and close monitoring, with CK levels gradually decreasing by 50% within 48 hours of cessation and supportive care.