Lopressor/drug interactions

Metoprolol
Clinical data
Trade names	Lopressor, Toprol-xl
AHFS/Drugs.com	Monograph
MedlinePlus	a682864
[[Regulation of therapeutic goods \|Template:Engvar data]]	US FDA: Metoprolol;
Pregnancy; category	AU: C ; US: C (Risk not ruled out) ; ;
Routes of; administration	Oral, IV
ATC code	C07AB02 (WHO) ;
Legal status
Legal status	In general: ℞ (Prescription only);
Pharmacokinetic data
Bioavailability	12%
Metabolism	Hepatic via CYP2D6, CYP3A4
Elimination half-life	3-7 hours
Excretion	Renal
Identifiers
	IUPAC name (RS)-1-(Isopropylamino)-3-[4-(2-methoxyethyl)phenoxy]propan-2-ol;
CAS Number	51384-51-1 ;
PubChem CID	4171;
IUPHAR/BPS	553;
DrugBank	DB00264 ;
ChemSpider	4027 ;
UNII	GEB06NHM23;
KEGG	D02358 ;
ChEBI	CHEBI:6904 ;
ChEMBL	ChEMBL13 ;
E number	{{#property:P628}}
ECHA InfoCard	{{#property:P2566}}Lua error in Module:EditAtWikidata at line 36: attempt to index field 'wikibase' (a nil value).
Chemical and physical data
Formula	C15H25NO3
Molar mass	267.364 g/mol
3D model (JSmol)	Interactive image;
Melting point	120 °C (248 °F)
	SMILES O(c1ccc(cc1)CCOC)CC(O)CNC(C)C;
	InChI InChI=1S/C15H25NO3/c1-12(2)16-10-14(17)11-19-15-6-4-13(5-7-15)8-9-18-3/h4-7,12,14,16-17H,8-11H2,1-3H3 ; Key:IUBSYMUCCVWXPE-UHFFFAOYSA-N ;
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Catecholamine-depleting drugs

Catecholamine-depleting drugs (e.g., reserpine) may have an additive effect when given with beta-blocking agents or monoamine oxidase (MAO) inhibitors.

Observe patients treated with Lopressor plus a catecholamine depletor for evidence of hypotension or marked bradycardia, which may produce vertigo, syncope, or postural hypotension. In addition, possibly significant hypertension may theoretically occur up to 14 days following discontinuation of the concomitant administration with an irreversible MAO inhibitor.

Digitalis glycosides and beta blockers

Both digitalis glycosides and beta blockers slow atrioventricular conduction and decrease heart rate. Concomitant use can increase the risk of bradycardia. Monitor heart rate and PR interval.

Calcium channel blockers

Concomitant administration of a beta-adrenergic antagonist with a calcium channel blocker may produce an additive reduction in myocardial contractility because of negative chronotropic and inotropic effects.

Risk of Anaphylactic Reaction

While taking beta blockers, patients with a history of severe anaphylactic reaction to a variety of allergens may be more reactive to repeated challenge, either accidental, diagnostic, or therapeutic. Such patients may be unresponsive to the usual doses of epinephrine used to treat allergic reaction.

General Anesthetics

Some inhalation anesthetics may enhance the cardiodepressant effect of beta blockers (see WARNINGS, Major Surgery).

CYP2D6 Inhibitors

Potent inhibitors of the CYP2D6 enzyme may increase the plasma concentration of Lopressor which would mimic the pharmacokinetics of CYP2D6 poor metabolizer (see pharmacokinetics section). Increase in plasma concentrations of metoprolol would decrease the cardioselectivity of metoprolol. Known clinically significant potent inhibitors of CYP2D6 are antidepressants such as fluvoxamine, fluoxetine, paroxetine, sertraline, bupropion, clomipramine, and desipramine; antipsychotics such as chlorpromazine, fluphenazine, haloperidol, and thioridazine; antiarrhythmics such as quinidine or propafenone; antiretrovirals such as ritonavir; antihistamines such as diphenhydramine; antimalarials such as hydroxychloroquine or quinidine; antifungals such as terbinafine.

Hydralazine

Concomitant administration of hydralazine may inhibit presystemic metabolism of metoprolol leading to increased concentrations of metoprolol.

Alpha-adrenergic agents

Antihypertensive effect of alpha-adrenergic blockers such as guanethidine, betanidine, reserpine, alpha-methyldopa or clonidine may be potentiated by beta-blockers including Lopressor. Beta-adrenergic blockers may also potentiate the postural hypotensive effect of the first dose of prazosin, probably by preventing reflex tachycardia. On the contrary, beta adrenergic blockers may also potentiate the hypertensive response to withdrawal of clonidine in patients receiving concomitant clonidine and beta-adrenergic blocker. If a patient is treated with clonidine and Lopressor concurrently, and clonidine treatment is to be discontinued, stop Lopressor several days before clonidine is withdrawn. Rebound hypertension that can follow withdrawal of clonidine may be increased in patients receiving concurrent beta-blocker treatment.

Ergot alkaloid

Concomitant administration with beta-blockers may enhance the vasoconstrictive action of ergot alkaloids.

Dipyridamole

In general, administration of a beta-blocker should be withheld before dipyridamole testing, with careful monitoring of heart rate following the dipyridamole injection.^[1]