Frequently, haematological patients undergo highly complex and intensive treatment protocols, so a high risk of drug–drug interactions could be expected.

To determine prevalence of clinically relevant drug–drug interactions, to identify the most frequent drug–drug interactions and associated risk factors.

A prospective, observational and descriptive study was carried out from November 2012 to February 2013. Twice a week, every patient’s treatment sheet was collected. Each medication list was screened through two databases: Thomson MicromedexTM and Drug Interaction FactsTM. All identified potential drug–drug interactions with a moderate or higher severity rating were recorded. Summary statistics were used to describe patient and disease characteristics, most often prescribed drugs, and frequency, types and classification of drug–drug interactions. Multiple logistic regression models were used to identify risk factors associated with drug–drug interactions.

A total of 2061 drug–drug interactions were detected in 317 treatment sheets from 58 patients. The prevalence of treatment sheets with drug–drug interactions by Micromedex and Drug Interaction Facts databases were 74.1% and 56.8%, respectively. Azole antifungals, immunosuppressive drugs, antiemetics, antidepressants, acid suppressants and corticosteroids were the most frequent involved drugs. In multivariate analysis, the main risk factor associated with increased odds for drug–drug interactions was a higher number of non-antineoplastic drugs.

The prevalence of drug–drug interactions was common, with immunosuppressant and azole antifungal agents being the most commonly involved drugs. The factor having the greatest influence on drug–drug interactions was a higher number of non-antineoplastic drugs.