• Espen Molden and Olav Spigset.
• Farmasøytisk institutt, Universitetet i Oslo, Norway. emolden@farmasi.uio.no
• Tidsskr. Nor. Laegeforen. 2011 Sep 20;131(18):1777-9.

BackgroundMetoprolol, the most commonly used beta-receptor antagonist in Norway, is eliminated mainly via the enzyme cytochrome P450 (CYP) 2D6. This enzyme is inhibited to a varying extent by antidepressants. The aim of this article is to provide an overview of the interactions between metoprolol and antidepressants with an emphasis on CYP2D6 inhibition.Material And MethodsRelevant literature was identified by a PubMed search using the word "metoprolol" combined with generic names of antidepressant drugs.ResultsThe potent CYP2D6 inhibitor paroxetine has been shown to increase the biologically available dose of metoprolol about 4- to 6-fold. The same degree of increase is expected for the two other potent CYP2D6 inhibitors in the class, fluoxetine and bupropion. Severe bradycardia and atroventricular block has been reported in patients who have taken metoprolol in combination with these three drugs. Escitalopram, citalopram and duloxetine are less potent CYP2D6 inhibitors, and have been shown to cause 2- to 3-fold increases in biologically available dose of metoprolol. Other antidepressants, such as sertraline, venlafaxine, mianserin and mirtazapine, inhibit CYP2D6 to little or no extent, and are not expected to cause clinically relevant interactions with metoprolol.ConclusionMetoprolol should not be used concomitantly with paroxetine, fluoxetine or bupropion due to extensive interactions and the risk of serious adverse effects. Dose reductions of metoprolol should be considered for combined treatment with citalopram, escitalopram or duloxetine, while concurrent use with sertraline, venlafaxine, mianserin and mirtazapine should be safe.

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