Prevalence of potential drug-drug interactions and its associated factors in a Brazilian teaching hospital.

PURPOSE: The hazards of prescribing many drugs, including side-effects, drug-drug interactions (DDI) and difficulties of compliance have long been recognized as particular problems when prescribing. This study estimates the rate and factors associated with potential DDI in prescriptions from wards of a Brazilian teaching hospital.
METHODS: Data were retrieved from wards of a teaching hospital (300 beds) handwritten prescription, once a week during a period of 4 months in 2004. Potential DDI were identified using DrugReax system. Patient's age and gender, number of prescribers; number of drugs and therapeutic drug classes on prescriptions were explored as associated factors to DDI.
RESULTS: The overall frequency of potential DDI was 49.7%. The frequency of the potentially major DDI was 3.4%, with digoxin-hydrochlorothiazide as the most common interacting pair. The rate of potential DDI was significantly associated to in-patients' gender [woman, Odds ratio (OR)=1.23 (P=0.035)], age=55 years old [OR=1.5 (P=0.0008)], number of therapeutic drug class (ATC code, level 1)=4 [OR=5.5 (P=0.0000), cardiology patients [OR=7.87 (P=0.0000)] hospitalized at weekends [OR=1.24 (P=0.039)] and having digoxin prescribed [OR=16.79 (P=0.0000)]. A positive correlation was found between DDI, patient's age, number of drugs and therapeutic action ATC codes were significant, controlling for gender (Pearson's r=0.628, P=0.001).
CONCLUSIONS: Cardiology women inpatients, age more then 55 years old, 7 or more drugs prescribed (including digoxin) and hospitalized at weekends should be closely monitored for adverse outcomes from DDI. A collaborative approach toward drug selection is strongly recommended, as well as electronic prescribing and development of pharmaceutical care in Brazilian hospitals.