Population-based severity, onset and type of drug-drug interactions in prescriptions.

Inappropriate drug combinations occur frequently and may lead to serious adverse events. In Iran, drug overdose and interactions are relatively common but rarely reported and are mainly derived from admitted subjects. The aim of this study was to determine the prevalence of possible drug-drug interactions via a population database survey in Mashhad, Iran. In this survey all prescriptions paid by insurance companies in the period 21rst March 2006 to 20th March 2008 were studied retrospectively. Data were gathered from the Division of Rational Use Drug, Food and Drug Vice Chancellor of Mashhad University of Medical Sciences, Iran. Drug interactions were categorized based on severity, onset and dynamic/kinetic nature. Incidence was calculated based on the number of interactions/1000 prescriptions. In total 11,562,808 prescriptions were studied, among which 5% showed interactions. Two hundred and four types of potential interactions were detected. Belladonna, phenytoin sodium, cimetidine, propranolol hydrochloride, gentamicin, acetylsalicylic acid (ASA), Antacid, theophylline and carbamazepine were the most common medications. Among them, 54% showed dynamic and 34% kinetic interactions, 11% were categorized to be both and 76% displayed rapid-onset interactions. Moderate interactions were the most dominant (70%) phenomenon. Dynamic and kinetic interactions significantly differed with respect to the onset of interactions (P < 0.001). A rather different pattern of drug-drug interaction exists in Iran, highlighting the need for a nationwide program on related education and a stronger focus on severe and rapid-onset interactions. Further studies warrant the need to explore high-risk patients.