Adverse drug reactions caused by drug-drug interactions reported to Croatian Agency for Medicinal Products and Medical Devices: a retrospective observational study

Aim

To analyze potential and actual drug-drug interactions reported to the Spontaneous Reporting Database of the Croatian Agency for Medicinal Products and Medical Devices (HALMED) and determine their incidence.

Methods

In this retrospective observational study performed from March 2005 to December 2008, we detected potential and actual drug-drug interactions using interaction programs and analyzed them.

Results

HALMED received 1209 reports involving at least two drugs. There were 468 (38.7%) reports on potential drug-drug interactions, 94 of which (7.8% of total reports) were actual drug-drug interactions. Among actual drug-drug interaction reports, the proportion of serious adverse drug reactions (53 out of 94) and the number of drugs (n?=?4) was significantly higher (P?ConclusionThe study confirmed that the Spontaneous Reporting Database was a valuable resource for detecting actual drug-drug interactions. Also, it identified drugs leading to serious adverse drug reactions and deaths, thus indicating the areas which should be in the focus of health care education.Adverse drug reactions (ADR) are among the leading causes of mortality and morbidity responsible for causing additional complications (1,2) and longer hospital stays. Magnitude of ADRs and the burden they place on health care system are considerable (3-6) yet preventable public health problems (7) if we take into consideration that an important cause of ADRs are drug-drug interactions (8,9). Although there is a substantial body of literature on ADRs caused by drug-drug interactions, it is difficult to accurately estimate their incidence, mainly because of different study designs, populations, frequency measures, and classification systems (10-15).Many studies including different groups of patients found the percentage of potential drug-drug interactions resulting in ADRs to be from 0%-60% (10,11,16-25). System analysis of ADRs showed that drug-drug interactions represented 3%-5% of all in-hospital medication errors (3). The most endangered groups were elderly and polimedicated patients (22,26-28), and emergency department visits were a frequent result (29). Although the overall incidence of ADRs caused by drug-drug interactions is modest (11-13,15,29,30), they are severe and in most cases lead to hospitalization (31,32).Potential drug-drug interactions are defined on the basis of on retrospective chart reviews and actual drug-drug interactions are defined on the basis of clinical evidence, ie, they are confirmed by laboratory tests or symptoms (33). The frequency of potential interactions is higher than that of actual interactions, resulting in large discrepancies among study findings (24).A valuable resource for detecting drug-drug interactions is a spontaneous reporting database (15,34). It currently uses several methods to detect possible drug-drug interactions (15,29,35,36). However, drug-drug interactions in general are rarely reported and information about the ADRs due to drug-drug interactions is usually lacking.The aim of this study was to estimate the incidence of actual and potential drug-drug interactions in the national Spontaneous Reporting Database of ADRs in Croatia. Additionally, we assessed the clinical significance and seriousness of drug-drug interactions and their probable mechanism of action.