Prevalence of potential drug–drug interactions in bone marrow transplant patients

Objective To assess the prevalence of potential drug–drug interactions (DDIs) in bone marrow transplantation (BMT) patients at the time of pre-infusion (day −1), to describe the potential DDIs and assess their frequency and severity. Setting The study was developed in a tertiary care hospital in São Paulo, Brazil. Method Cross-sectional study based on examining the medical prescriptions from the pre-infusion day (day −1) of 70 BMT patients. Potential DDIs were analyzed using Drug-Reax^® and categorized according to levels of severity, evidence, and onset (rapid and delayed). Only interactions of major or moderate severity were included in the potential DDI analysis. Main outcome measure: Prevalence of potential DDIs in patients during the preinfusion phase of BMT. Results Data were analysed for 70 BMT patients. The median age was 36.5 years; 52.9% (37) of the patients were male, and 65.7% (46) were undergoing autologous BMT. The patients received a median of 8 drugs each. Up to 128 potential DDIs were detected, 60.0% (42) of patients had at least 1 potential DDI and 21.4% (15) were exposed to at least 1 major potential DDI. The most commonly involved drugs were cyclosporine (9, 28.1%), phenytoin (8, 25%) and fluconazole (5, 15.6%). Most potential DDIs had moderate severity (110, 85.9%), a pharmacokinetic mechanism (67, 52.3%), and were classified as delayed onset (106, 82.8%). For major interactions, fluconazole + sulfamethoxazole/trimethoprim, diazepam + fentanyl, fluconazole + levofloxacin and fentanyl + fluconazole were the most frequent. Conclusions The prevalence of potential DDIs during the conditioning period of BMT was high as a consequence of the therapeutic complexity of the procedure. Most potential DDIs identified in the study may result in clinically relevant consequences as they could lead to nephrotoxicity, cardiotoxicity, and other undesirable adverse effects. Careful monitoring of clinical and laboratory parameters is essential to ensure a successful BMT and to avoid adverse drug events related to DDI.