The present study intended to identify and analyze the significance of drug–drug interaction (DDI) in critically ill patients.

All consecutive adult patients admitted to a medical/surgical ICU of a tertiary-care hospital, from September 2006 to April 2007, were included in this prospective observational study. Patients who stayed less than 48 hours were excluded. All the drugs that were given during the ICU stay were checked for the presence of potential interactions as per the reference manual. DDIs that were detected clinically or through investigations were recorded and also any therapeutic actions taken for DDIs were noted.

The study included 400 patients (Table 1). Sixty-four percent (n = 256) of patients from the study cohort had potential DDI. The total number of potential DDI found in all prescriptions was 602; however, only in 34% (n = 208) was DDI actually observed; of which a clinically relevant interaction (requiring drug modification or other therapeutic intervention) was observed in 49.5% (103 of 208). The average number of drugs used per patients was nine (SD ± 4) and potential DDIs found per patient were two (SD ± 2). The drug interactions were classified into three groups, minor (55.29%), moderate (23.08%) and major (21.63%) according to the severity of and requirement for drug modification.

DDIs are common in the ICU population in the presence of polypharmacy, and a substantial proportion of them are clinically relevant.