Drug Interactions as a cause of Adverse Drug Reactions in a Tertiary Care Hospital

Abstract

Objectives: Drug-drug interactions (DDIs) are an important issue in clinical practice as management of co-morbidities necessitates polypharmacy and some of these interactions can transmute into or accentuate adverse drug reactions (ADRs). The objective was to estimate the proportion of ADRs due to DDIs and to describe the pattern of drug-drug interactions that resulted in ADRs. Materials and Methods: Cross-sectional study was done in the Department of Pharmacology of a Government Medical College in Kerala for a period of 1 year after getting clearance from the Institutional Ethics Committee. ADR reports submitted to the ADR Monitoring Centre from June 2015 to May 2017 formed the study material and details were entered in a structured proforma. Each suspected drug and concomitant drugs were entered in MICROMEDEX®, MEDSCAPE, and LEXICOMP drug interaction softwares to identify all potential DDIs (pDDIs). The interactions which matched with ADR description were considered to be the probable cause of that ADR. SPSS software version 16 was used for data analysis. Descriptive data were expressed as frequencies and percentages. Results: Of the 345 ADR patients reported during the study period, 249 had concomitant drugs (mean 2.84±1.85 drugs/patient) from whom we identified 295 pDDIs (mean 1.18 ± 1.59 pDDIs/patient). Of the 295 pDDI, 30 matched the description of ADR, thus the proportion of ADRs due to DDIs was 12.05% (30 out of the 249 ADRs). Aspirin with Clopidogrel (n=5) and Heparin with Clopidogrel (n=5) topped the list of interactions contributing to ADR. Amongst the 30 suspected drug interactions causing ADR, 23 (76.67%) were pharmacodynamic, 21(70%) were of major severity and in 27(90%) the time of onset were not specified. Conclusions: Drug-drug interactions attributed to 12.05% of the ADRs in which data on concomitant drugs were available. Pharmacodynamic interactions (76.7%) contributed to sADRs more than pharmacokinetic interactions.