Cases of the quarter: Rhabdomyolysis following co-prescription of fusidic acid and atorvastatin

The  placebo-corrected  incidence  of  rhabdomyolysis  in  a  systematic review of 20 statin trials was 1.6/100,000 per year. It is likely to be higher than this  in  everyday  clinical  practice  when  statins  are  knowingly  or  inadvertently co-prescribed with drugs that interfere with their metabolism. We report a case of  rhabdomyolysis  causing  muscle  weakness  and  prolonging  an  episode  of  dialysis-dependent acute kidney injury, which occurred when fusidic acid was co-prescribed with atorvastatin. Renal function and muscle power recovered when both drugs were withdrawn. We found four other cases of rhabdomyolysis with fusidic acid and  atorvastatin  and  three  with  fusidic  acid  and  simvastatin  in  the  literature,  a
review of which suggests that the risks of rhabdomyolysis vary with the extent to which an individual statin is dependent for its metabolism on the cytochrome P450 3A4 isoenzyme and the degree to which this isoenzyme’s activity is inhibited by a particular antimicrobial. Of note, the interaction between statins and fusidic acid did not feature in seven of eight recent reviews of statin toxicity. Our case report  highlights  the  importance  of  close  monitoring  of  patients  on  statins, especially when new drugs are started or if patients become unwell, by checking creatine  kinase  and  liver  function  tests  and  by  examining  for  new  muscle weakness.  Our  review  of  statin–antimicrobial  drug  interactions  suggests  that fusidic acid is another CYP450 3A4 enzyme inhibitor with the potential to cause rhabdomyolysis when co-prescribed with simvastatin and atorvastatin.