Increased Rates of Rhabdomyolysis in Male Hematopoietic Cell Transplantation Recipients Taking Sirolimus and Trimethoprim/Sulfamethoxazole.

Hematopoietic cell transplantation (HCT) offers long-term cure against early morbidity and mortality of hemoglobinopathies, such as sickle cell disease (SCD) and beta-thalassemia. Following HCT, sirolimus is an immunosuppressant used to prevent graft-versus-host disease (GVHD) while receiving trimethoprim-sulfamethoxazole (TMP-SMX) for Pneumocystis jirovecii prophylaxis and other antimicrobial agents (including acyclovir). One rare adverse event associated with both drugs is rhabdomyolysis, defined as creatine kinase (CK) elevation at least 5 to 10 times the upper limit of normal. This study was conducted to evaluate the rate of and risk factors for developing rhabdomyolysis in the post-HCT setting. Across 4 haploidentical and matched related donor (MRD) nonmyeloablative protocols, CK levels were prospectively monitored and patients were retrospectively identified for rhabdomyolysis. The rhabdomyolysis was graded based on the severity of CK elevation and other organ injury. At diagnosis, patients were queried for concurrent medication use (ie, sirolimus, TMP-SMX, acyclovir, or statins), sex, age, donor genotype, and time from transplantation. Among 127 patients with mostly SCD, rhabdomyolysis occurred in 22 (17%), including 2 recipients of haploidentical donor HCT and 20 recipients of MRD HCT. The time to the development of rhabdomyolysis was 61 and 73 days for the 2 recipients of haploidentical HCT and a median of 73 days for the MRD HCT recipients. Among the 22 patients who developed rhabdomyolysis, 20 (91%) were receiving sirolimus (2 haploidentical HCT recipients and 18 MRD HCT recipients), and 14 (64%) were also receiving TMP-SMX (all in the MRD HCT group). Seventy-five percent of the haploidentical donors and 69% of the MRDs had sickle cell trait. All but 2 patients with rhabdomyolysis were male. No patients who developed rhabdomyolysis were receiving statins at any point. Higher-than-expected rates of rhabdomyolysis were found post-transplantation for patients with SCD and beta-thalassemia. Contributing risk factors included immunosuppression with sirolimus, TMP-SMX, male sex, and sickle trait donor. These factors differ from the excessive muscle strain or injury, seizures, infections, or HMG-CoA inhibitors typically identified in non-HCT recipients.