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Updated: Aug 19, 2026

Quantification of the Immunosuppressant Tacrolimus on Dried Blood Spots Using LC-MS/MS
Published on: November 8, 2015
Clinical relevance of sirolimus drug interactions in transplant patients
B Sádaba1, M A Campanero, E G Quetglas
1Department of Clinical Pharmacology, University Clinic of Navarra, Pamplona, Spain.
Abstract:
Sirolimus, a new immunosuppressant drug; is metabolized by cytochrome P450 3A4 (CYP3A4) and is a substrate of the P-glycoprotein drug efflux pump. The CYP3A4/P-glycoprotein system is mainly localized in the liver and intestine. It is responsible for the severe first pass metabolism of sirolimus with a low bioavailability. Drugs like voriconazole, itraconazole, fluconazole, and erytrhomycin may decrease the metabolic activity of this enzymatic system. This report documents in five patients that coadministration of these antimicrobials with sirolimus increases the blood concentrations of the immunosuppressant. The dose-normalized trough blood concentration showed a mean increase of sevenfold with the coadministration of these drugs. It is essential to monitor the blood sirolimus concentrations and to adjust the sirolimus doses before and after coadministration of these drugs.
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