Rhabdomyolysis caused by tocolysis with oral ritodrine hydrochloride in a pregnant patient with myotonic dystrophy.

Drug-induced rhabdomyolysis during pregnancy is extremely rare. We report here a rare case of ritodrine-hydrochloride-induced rhabdomyolysis in a pregnant patient with myotonic dystrophy. A 32-year-old primigravida was admitted because of premature labor at 31 weeks of gestation. She had been diagnosed as having myotonic dystrophy by electromyographic investigations and abnormal serum creatinine phosphokinase (CPK) levels. Tocolysis was initiated with oral ritodrine hydrochloride (15 mg/day) alone. There was a prompt response to the ritodrine hydrochloride. Three days after administration began, serum CPK levels had become markedly elevated to 10,897 mg/dl and myoglobinuria was detected (1,800 ng/dl), suggesting the presence of rhabdomyolysis. There was no evidence of worsening of the myotonic symptoms. Tocolysis was stopped immediately, and the laboratory data improved gradually. At 37 weeks of gestation, she spontaneously delivered a healthy male baby. Rhabdomyolysis has been recognized as a complication of tocolytic therapy with ritodrine hydrochloride. Therefore, beta-adrenergic agents should be used with great care, especially for patients with myotonic dystrophy, because of these agents' tendency to aggravate or precipitate myotonia and to induce rhabdomyolysis.