Potential Drug-Drug Interactions in primary health care in Southern Brazil

INTRODUCTION: The primary health care services must guarantee acess to medicines. Nevertheless, the irrational drug use still is a challenge to health systems and could harm their users. The aim of this study is to determine the prevalence of potential drug-drug interactions (P-DDI) and associated factors in Primary Health Care  in Southern Brazil.

METHODS: 701 patients of primary health care were interviewed. The main variable is P-DDI defined by two online database applications. Severity and clinical features were described. The prevalence of P-DDI  and interaction-prescription rate were calculated. The association between P-DDI and some characteristics of patients and services was estimated using a Poisson regression model ajusted by sex and age.

RESULTS: 463 patients had two or more prescription drugs, with a mean age of 45.4 years + / - 19.8 (no gender differences). It was identified 736 P-DDI in 228 patients (prevalence=49.2%). The drug pair which caused more P-DDI was enalapril maleate and hydrochlorothiazide. Regarding the severity, 72.8% of interactions were moderate, 21.7% were minor and 5.4% were major interactions. The highest interaction/prescription rate is amlodipine (3,5).  P-DDI were associated with duration of treatment (5 years and more RP=3,8; P<0,00001) and number of medicines (5 and more RP=1,6; p<0,00001)

CONCLUSIONS: P-DDI prevalence is high in primary care although most of them moderate. Patients with long term treatments and excessive medicines must be closely monitored by doctors and pharmacists to prevent harm.