Azoospermia in a renal transplant recipient during sirolimus (rapamycin) treatment.

Sirolimus is used as a powerful immunosuppressant drug in patients after organ transplantation. It was shown to block spermatogenesis by interrupting the stem cell factor/c-kit system. Oligozoospermia was shown in single patients. In addition, a decrease of testosterone and an increase of gonadotropin levels were observed. We report on a young patient who showed azoospermia during the treatment with sirolimus after renal transplantation. After changing the immunosuppression to tacrolimus, spermatogenesis of the patient recovered. Five months after cessation of the treatment with sirolimus, a sperm concentration of 8 x 10(6) ml(-1) was found. Depression of spermatogenesis is an important side effect in younger men who aspire paternity, so that waiving of sirolimus is advisable in these patients.