Simvastatin-associated rhabdomyolysis after coadministration of macrolide antibiotics in two patients.

Two men, aged 83 and 78 years, who received stable therapy with simvastatin 80 mg/day were hospitalized 1-2 weeks after completion of short-term treatment with erythromycin and clarithromycin, respectively. Both patients were admitted with myalgia, muscle weakness, functional disability (inability to raise arms and legs), and serum creatine kinase levels more than 60 times the upper limit of normal (ULN). Substantial elevations in aspartate aminotransferase (> 30 times the ULN) and alanine aminotransferase (> 7 times the ULN) levels were also observed. Rhabdomyolysis was diagnosed in both patients. Both recovered, but the combined events resulted in almost 40 days of hospitalization, the cost of which is considerable. According to the Naranjo adverse drug reaction probability scale, the likelihood that the rhabdomyolysis was secondary to a simvastatin-macrolide interaction was probable. Four cases of rhabdomyolysis after therapy with combined simvastatin and clarithromycin have been reported previously, but this is apparently the first report of rhabdomyolysis after coadministration of erythromycin. The interacting mechanism likely was inhibited cytochrome P450 (CYP) 3A4 metabolism and possibly P-glycoprotein transport of simvastatin as well. Previous reports of simvastatin-clarithromycin-related events involved additional drugs that inhibited CYP3A4 and P-glycoprotein. However, this was not the situation with our two patients. To prevent future events, it is crucial that clinicians recognize the interaction risk associated with concurrent use of simvastatin and clarithromycin or erythromycin. The risk could be managed by temporary interruption of simvastatin treatment or administration of a noninteracting antimicrobial agent.