The impact of CYP2D6 mediated drug–drug interaction: a systematic review on a combination of metoprolol and paroxetine/fluoxetine

AIM: Metoprolol (a CYP2D6 substrate) is often co‐prescribed with paroxetine/fluoxetine (a CYP2D6 inhibitor) because the clinical relevance of this drug–drug interaction (DDI) is still unclear. This review aimed to systematically evaluate the available evidence and quantify the clinical impact of the DDI. METHOD: Pubmed, Web of Science, Cochrane Library and Embase were searched for studies reporting on the effect of the DDI among adults published until April 2018. Data on pharmacokinetics, pharmacodynamics and clinical outcomes from experimental, observational and case report studies were retrieved. The protocol of this study was registered in PROSPERO (CRD42018093087). RESULTS: We found nine eligible articles that consisted of four experimental and two observational studies as well as three case reports. Experimental studies reported that paroxetine increased the AUC of metoprolol three to five times, and significantly decreased systolic blood pressure and heart rate of patients. Case reports concerned bradycardia and atrioventricular block due to the DDI. Results from observational studies were conflicting. A cohort study indicated that the DDI was significantly associated with the incidence of early discontinuation of metoprolol as an indicator of the emergence of metoprolol‐related side effects. In a case–control study, the DDI was not significantly associated with bradycardia. CONCLUSION: Despite the contradictory conclusions from the current literature, the majority of studies suggest that the DDI can lead to adverse clinical consequences. Since alternative antidepressants and beta‐blockers with comparable efficacy are available, such DDIs can be avoided. Nonetheless, if prescribing the combination is unavoidable, a dose adjustment or close monitoring of the metoprolol‐related side effects is necessary.