Potential drug interactions in patients with rheumatoid arthritis.

INTRODUCTION The term polypharmacy, meaning the concomitant use of multiple medications by one individual, has been widely reported in institutionalized or elderly patients. It can, however, occur in patients with chronic diseases, such as rheumatoid arthritis (RA). OBJECTIVE To quantify polypharmacy in a group of RA patients and to assess the risk of potential undesirable interactions between medications used for managing RA and those used for non-chronic diseases. METHODS A cohort study was carried out with 103 RA patients registered at the Strategy of Access to Medications from the Brazilian Health Ministry, at the School of Pharmacy of the city of Florianópolis, state of Santa Catarina. Patients were monthly followed up by use of form completion. Drug interactions were identified by use of the Drugdex System - Thomson Micromedex® - Interactions database. RESULTS Polypharmacy was found in 95.1% of the patients, and 19 potential undesirable interactions were observed between the drugs used by 74 patients (mean of 3.0 ± 1.2 interactions/patient). All potential interactions were related to methotrexate. Omeprazole was the major representative, accounting for 29.3% of the interactions, followed by diclofenac sodium (17.6%), and metamizole sodium (13.2%). CONCLUSION Considering that this study confirms that polypharmacy is a common therapeutic practice in RA patients, it is worth emphasizing the need for greater surveillance regarding the adverse effects or effectiveness reduction of certain drugs due to drug interaction.