Exacerbation of cyclosporine toxicity by concomitant administration of erythromycin.

Cyclosporine (CsA), an immunosuppressive drug widely used in clinical organ transplantation, causes a variety of side effects, including parenchymal complications of nephrotoxicity and hepatotoxicity. Erythromycin ethinylsuccinate (EES), a macrolide antibiotic frequently administered to transplant patients afflicted with pneumonias caused by Mycoplasma pneumoniae and Legionella pneumophila, markedly potentiated parenchymal drug toxicity in nine (three renal and six cardiac) CsA-treated allograft recipients. The mean and median blood urea nitrogen (BUN), creatinine, and total bilirubin increased upon initiation of EES treatment: in the renal recipients from 27, 1.7, and 0.5 mg/dl, respectively, before, to a mean and median of 81/101, 8.3/3.9, and 2.1/1.2 mg/dl during, and to 72/22, 1.9/1.7, and 0.6/0.5 mg/dl after cessation of EES treatment. The median serum radioimmunoassay (RIA)-determined CsA trough value of 147 ng/ml prior, rose to a zenith of 1125 ng/ml during, EES therapy. In the six cardiac recipients, the mean and median BUN, creatinine, and total bilirubin of 51/45, 1.5/1.3, 1.2/1.3 mg/dl, respectively, before, rose to 100/91, 3.7/3.6, and 2.3/2.1 mg/dl during, and fell to 49/44, 1.8/2.1, and 1.0/0.8 mg/dl after, cessation of EES. The mean serum CsA trough value of 185 ng/ml rose to 815 ng/ml during EES administration. Since EES and CsA are both metabolized by the hepatic cytochrome P450 mixed-function oxidase system, simultaneous use of these two drugs may decrease CsA metabolism, with consequent elevation of blood levels and induction of CsA toxicity. Therefore, blood level monitoring and careful regulation of CsA dose are necessary, in order to achieve the safe use of EES in transplant recipients.