Impact of frailty, melphalan pharmacokinetics, and pharmacogenetics on outcomes post autologous hematopoietic cell transplantation for multiple myeloma.

Autologous hematopoietic cell transplantation (auto-HCT) using melphalan is the standard of care in the management of myeloma. Auto-HCT is a safe procedure with tolerable toxicity except in Asian-Indians. We hypothesized either one or a combination of factors: (1) frailty (assessed by IMWG frailty score), (2) generic melphalan pharmacokinetic area under the curve (AUC) assessed by high-performance liquid chromatography, and (3) pharmacogenetics of glutathione S-transferase (GSTP1) assessed by Sanger sequencing, to be associated with toxicity and survival outcomes post auto-HCT. Disease response was evaluated by IMWG response criteria at day +100 post auto-HCT. Gastrointestinal (GI) toxicity, infections, hospital stay, progression-free survival (PFS) were also recorded. A total of 35 patients were evaluated over 2 years (2016-2018). Frailty, not HCT-comorbidity index correlated with GI toxicity and infections. Overall there was an 11-fold variation in melphalan AUC with a median of 27.88 mg h/L (10.06-110.26). Patients with AUC more than the median had more GI toxicity and infections. Patients with wild-type GSTP1 polymorphism had more GI toxicity and infections. Frailty, AUC, or GSTP1 polymorphism did not impact hospitalization duration or PFS. A combination of the factors frailty, melphalan pharmacokinetics, and pharmacogenetics impacts GI toxicity and infections after auto-HCT in myeloma.