Dr. Bob's Psychopharmacology Tips

SSRI inhibition of beta-blocker metabolism

Date: Sat, 07 Jun 1997 00:09:01 -0400
From: William Braden <braden@brown.edu>
Subject: SSRI inhibition of beta-blocker metabolism

Bob Hsiung wrote:

A medical student patient asked me the other day about the inhibition by fluoxetine of the metabolism of beta-blockers. I didn't recall anything like that, asked for a reference, and was diligently given a couple pages from Lippincott's Pharmacology Review, including the statement: "fluoxetine is a potent inhibitor of a hepatic cytochrome P-450 isoenzyme responsible for the elimination of ... some ... beta-adrenergic antagonist drugs".

Date: Sun, 08 Jun 1997 11:52:41 -0400
From: William Braden <braden@brown.edu>
Subject: SSRI inhibition of beta-blocker metabolism

Propranolol, metoprolol and timolol are metabolized by CP-450 IID6. Therefore, paroxetine, fluoxetine, sertraline, and other inhibitors of CP-450 IID6 (eg, cimetidine) may increase the levels of the beta-blockers mentioned above. Propranolol is also metabolized by CP-450 IA2 and therefore its level may rise when fluvoxamine is concomitantly used with propanolol (fluvoxamine is a potent inhibitor of CP-450 IA2).

--Padi Ghaeli, Pharm.D

Date: Mon, 9 Jun 1997 21:42:44 -0700 (PDT)
From: Talia Puzantian <talia@itsa.ucsf.edu>
Subject: SSRI inhibition of beta-blocker metabolism

My understanding is that metoprolol and timolol are primarily metabolized by 2D6; propranolol is metabolized by 2D6, 1A2, and others; and atenolol is mostly renally excreted (not metabolized).

Date: Tue, 10 Jun 1997 10:02:59 -0500
From: Larry Ereshefsky <Ereshefsky@uthscsa.edu>
Subject: SSRI inhibition of beta-blocker metabolism

In general, the more fat soluble beta blockers might interact with fluoxetine via a combination of strong inhibition at CYP 2D6 (important for propranolol and metoprolol), moderate inhibition at CYP2C, and weak (but dose related) inhibition at CYP3A4 and 1A2. In total the effect is less robust than with fluvoxamine, but possible -- there are case reports of bradycardia and lethargy with fluoxetine and fat soluble beta blockers. Sotalol and atenolol are less likely to interact.

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