Incidence of cocaine-associated rhabdomyolysis. STUDY HYPOTHESIS: Rhabdomyolysis is a common complication of cocaine use, and muscle symptoms fail to predict its development. STUDY POPULATION: A prospective, convenience sample of patients presenting to the emergency department of a large inner-city hospital with complaints related to cocaine use were eligible for inclusion. Patients were excluded if they had other potential causes of elevated creatine kinase (CK) levels or rhabdomyolysis. A control group comprised patients who were not cocaine users and satisfied the exclusion criteria. Sixty-eight patients were studied. METHODS: Initial evaluation included determination of the presence of muscle pain or swelling and total CK levels. Patients with a CK level of more than 800 U/L had additional tests, including a urine myoglobin, urine drug screen, and serum phosphorus. Rhabdomyolysis was defined by a serum CK level of more than 1,000 U/L (more than fivefold that of normal). CK levels were compared by two-tailed Student's t test. Muscle symptoms were compared with the development of rhabdomyolysis by Fisher's exact test. RESULTS: The CK level in the cocaine group was 931 +/- 1,785 U/L (mean +/- 1 SD). The CK level in the control group was 242 +/- 168 U/L (P = .028). Of the cocaine users, 24% (eight of 34) had rhabdomyolysis; one developed multiorgan failure and died. No patient in the control group had a CK level of more than 1,000 U/L. Only one cocaine user who developed rhabdomyolysis had muscle symptoms. Three cocaine users had muscle symptoms but did not develop rhabdomyolysis. No patient in the control group had muscle symptoms or developed rhabdomyolysis. Muscle symptoms did not predict the CK level (P = .55). CONCLUSION: This study revealed that 24% of the cocaine users had rhabdomyolysis. Many of the cases of rhabdomyolysis were not predictable from history or physical examination, making laboratory evaluation essential. 