Analysis of drug-drug interactions between psychiatric drugs in spontaneous adverse drug reaction reports from EudraVigilance

In psychiatric care, polypharmacy is common practice. The more drugs are used, the higher the likelihood of drug-drug interactions (DDI) and, consequently, the occurrence of adverse drug reactions (ADR). The aim of our study was to identify DDI between psychiatric drugs and to analyze their associated factors in spontaneous ADR reports contained in the European ADR database EudraVigilance. Out of 9287 ADR reports from EudraVigilance, 1811 reports with potential DDI (pDDI) were detected by the ABDATA interaction analysis. During the individual case assessment of the most frequently identified pDDI (n = 1342), 206 reports with DDI were found. These 206 reports were analyzed descriptively. Patients who experienced DDI were on average 52.6 (± 18.8) years old. Reports describing DDI were clearly more often classified as serious than those without DDI (81.1% versus 59.0%, p-value < 0.005). The DDI most frequently identified were tachycardia and QT prolongation (23.3%, 48/206), extrapyramidal symptoms (16.0%, 33/206), sedation (11.7%, 24/206) and seizures (11.7%, 24/206). Mirtazapine-quetiapine (26.3%, 10/48) was the interacting drug pair most commonly associated with tachycardia and QT prolongation. Patients experiencing tachycardia and QT prolongation were, on average, older (63.0 (± 16.2) years) and took more drugs (8.0 (± 5.3)) than the overall group of patients with DDI (6.0 (± 3.9)). DDI pose a considerable risk to patients treated with several combinations of psychiatric drugs. Checks for interactions and tight monitoring after initiating drug therapy can help to avoid serious DDI. Special attention should be paid to older patients taking more than one QT-interval prolonging drug.