Sirolimus and Male Fertility

I just came across an interesting paper published couple of years ago. Zuber et al (Am J Transplantion,July 2008) carried out an observational study in male patients aged 20-40 years who received a kidney transplant during 1995-2005 in France. Patients on sirolimus based immunosuppression had a significantly reduced total sperm count and a decreased proportion of motile spermatozoa compared to patients who did not receive sirolimus. Also, it was found that the fathered pregnancy rate (pregnancies/1000 patient years) was 5.9 and 92.9 in patients receiving sirolimus-based and sirolimus-free regimens, respectively. Of those patients in whom sirolimus treatment was interrupted, only half of the patients showed a significant improvement in sperm parameters. The authors concluded that sirolimus is associated with impaired spermatogenesis and may reduce male fertility. So, if you have a male transplant patient on sirolimus presenting with fertility issues, switching sirolimus to another agent like tacrolimus may help.