Interactions between cyclosporin A, indomethacin and 16,16-dimethyl prostaglandin E2: effects on renal, hepatic and gastrointestinal toxicity in the rat.

Rats were treated for 3 or 14 days with cyclosporin A (CsA, 50 mg/kg) or indomethacin (2 or 5 mg/kg) either alone or in combination, or with CsA plus 16,16-dimethylprostaglandin E2 (DMPGE2, 0.25 mg/kg). Hepatic and renal function were unaffected by treatment with indomethacin at either dose and only at the higher dose was severe intestinal ulceration observed. CsA caused renal and hepatic toxicity, evidenced by increased urine N-acetyl-beta-D-glucosaminidase activity, serum urea, creatinine and bilirubin and decreased serum albumin and total protein. In rats cotreated with CsA and either dose of indomethacin the increases in serum urea and creatinine and decreases in serum albumin and total protein were accentuated, but serum bilirubin was not further increased. Intestinal lesions were present in rats treated for 14 days with CsA plus the lower dose of indomethacin, but not in rats treated with either drug alone. In rats treated with DMPGE2 plus CsA, serum urea and creatinine were normal and urine N-acetyl-beta-D-glucosaminidase activity was reduced compared to rats treated with CsA alone, but DMPGE2 cotreatment had no effect on the CsA induced hyperbilirubinaemia. Hepatic microsomal cytochrome P-450 concentration and aminopyrine N-demethylase activity were lower in rats treated with CsA plus indomethacin than in untreated rats or those treated with either drug alone. Coadministration of indomethacin or DMPGE2 had no effect on serum trough CsA levels. The results are interpreted as showing an exacerbation by CsA of the intestinal toxicity of indomethacin, an increase by indomethacin in the renal toxicity of CsA and a protection by DMPGE2 against CsA renal toxicity. Possible mechanisms involving drug interactions and either hepatic cytochrome P-450, renal cyclooxygenase or other renal sites are discussed.