A 76-year-old man with hypercholesterolemia had been taking simvastatin for about 2 years prior to admission. He had also been taking several other drugs-for gastric ulcer, myocardial infarction and reflux esophagitis. He had experienced numbness in his upper and lower extremity muscles for a month before admission and in the 2 weeks prior to admission, he had been taking mosapride citrate for lack of appetite. The reason for hospitalization was muscle pain in both shoulders and difficulty in walking.
Echography on admission suggested bilateral renal cystic disease with dysfunction of the left kidney. Laboratory tests revealed reduced 24 hr creatinine clearance (CK : 47 mL/min). On the day of hospitalization, simvastatin was withdrawn due to the possibility of rhabdomyolysis, resulting in an improvement in CK and the muscular symptoms. Judging by the time course of the myopathy, simvastatin was thought to be a possible cause. Since simvastatin had been administered for the past 2 years, certain factors were considered to have increased its plasma levels and induce the myopathy. Among them were decreased excretion due to malfunction of the kidney, inhibition of p-glycoprotein by the omeprazole he had been taking for gastric ulcer and metabolic interaction with the mosapride citrate that was administered 2 weeks prior to admission. Both mosapride citrate and simvastatin are metabolized by cyp 3 A 4 and the protein binding affinity of mosapride citrate was highest (99%) among the drugs prescribed. So far there has been no other report of an interaction between simvastatin and mosapride citrate, a drug commonly used for digestive troubles.
In conclusion, in view of the myopathy that was apparently caused by the co-administration of these two drugs, it is necessary to observe special caution in the use of mosapride citrate.
