[Drug-drug interactions with risk of QT-prolongation. A epidemiological study in Belgian community pharmacies].

Introduction Community pharmacists have an important role in the management of drug-drug interactions (DD). One of the interactions that can lead to serious adverse drug events, more specifically Torsade de Pointes and sudden cardiac death, are DDI with risk of CT-prolongation. Many drugs from different therapeutic classes have been linked with the risk of QT-prolongation (as listed in the QT-drug lists of CredibleMeds]. Moreover, patient-specific risk factors should be taken into account. This leads to a complex risk estimation of QT-prolongation for each patient. Aim The aim of this study is to investigate the prevalence of DDI and the management of these interactions in community pharmacies, with special attention for DDI with a risk of QT-prolongation. Method This epidemiological study is based on data of an interuniversity, observational study in 534 Belgian community pharmacies with a last-year pharmacy student (November 2012 - March 2013), in which all drug-related problems (DRP) and associated interventions of the pharmacist were registered for drugs on prescription. In this study, all DRP that were registered as a DDI were selected. The evidence for these DD was verified in four information sources (DelphiCare, Medscape, Drugs.com, handbook 'Commentaren Medicatiebewaking'). Finally, an in-depth analysis was performed for DDI with risk of QT-prolongation. QT-prolonging drugs were identified with the QT-drug lists of CredibleMeds. Results In total, 64.962 prescriptions and 15.952 DRP were registered in the interuniversity study, of which 1858 DRP (11.6%) described as a DDI that was confirmed in at least one of the information sources. Of these interactions, 223 [12.0%] were linked with a risk of QT- prolongation. The majority of the concerned drugs are situated in list 1 of CredibleMeds (known risk of Torsade de Pointes). In 69 CT-prolonging DDI, two drugs of list 1 were involved. The most frequent QT-prolonging DDI was between escitalopram and quetiapine (N=11J. In 69.5% of the QT-prolonging DDI, an intervention was performed by the community pharmacist. In 47.8% of these interventions, the DDI was discussed with the patient. In 28.3% of the QT-prolonging DDI, the pharmacist contacted the physician. However, the proposed intervention was often considered unnecessary by the physician (42.9%). In only 4.5% of the interventions, the involved CT-prolonging drug was replaced by an alternative. Conclusion DDI represent an important part of the DRP in community pharmacies, including DDI with a risk of CT-prolongation (12% of the interactions). In the majority of the QT-prolonging DDI, at least one QT-prolonging drug of list 1 of CredibleMeds [known risk of Torsade de Pointes) was involved. In only 4.5% of the interventions, the involved QT-prolonging drug was replaced by an alternative.