Assessment of drug-related problems associated with narrow therapeutic index drugs: A prospective cohort study

A narrow therapeutic index drug (NTID) has a narrow window between its effective doses and doses that can cause adverse toxic effects, necessitating strict monitoring for drug safety. This study aimed to identify and classify the drug-related problems (DRPs) associated with the use of NTI drugs. A prospective cohort study was carried out in the in-patient departments of General Medicine, Paediatrics, Cardiology, and Neurology at a tertiary care hospital over a nine-month period. Patients of either gender receiving at least one NTID included after obtaining their consent. The patients were followed until their discharge for any DRP occurrence. The list of the NTIDs was compiled through a review of literature review and the hospital's formulary. Hepler & Strand's classification was adopted to classify the identified DRPs. The odds ratio with a 95% confidence interval was used to determine the predictors for DRP occurrence. A total of 241 DRPs associated with NTIDs were identified among 120 patients. Drug–drug interactions accounted for 61% of the DRPs, followed by subtherapeutic dosing (18.26%) and adverse drug reactions (9.96%). On average, each patient experienced 2.74 DRPs. The predictors for DRP occurrence included gender (odds ratio [OR] 2.65, p = .012), comorbid conditions (OR 2.947, p < .001), polypharmacy involving more than 11 drugs (OR 3.987, p < .033), and a hospital stay exceeding 7 days (OR 1.087, p = .022). Despite providing the best therapeutic care, DRPs associated with NTIDs persist and can compromise patient safety. Therefore, involving clinical pharmacists in the early detection of DRPs can enhance overall patient safety.