Lopressor/warnings

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 Y
PubChem CID	4171
IUPHAR/BPS	553
DrugBank	DB00264 Y
ChemSpider	4027 Y
UNII	GEB06NHM23
KEGG	D02358 Y
ChEBI	CHEBI:6904 Y
ChEMBL	ChEMBL13 Y
E number	{{#property:P628}}
ECHA InfoCard	{{#property:P2566}}
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 Y Key:IUBSYMUCCVWXPE-UHFFFAOYSA-N Y
(verify)

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

WARNING See full prescribing information for complete boxed warning. Ischemic Heart Disease: Following abrupt cessation of therapy with certain beta-blocking agents, exacerbations of angina pectoris and, in some cases, myocardial infarction have occurred. When discontinuing chronically administered Lopressor, particularly in patients with ischemic heart disease, the dosage should be gradually reduced over a period of 1-2 weeks and the patient should be carefully monitored. If angina markedly worsens or acute coronary insufficiency develops, Lopressor administration should be reinstated promptly, at least temporarily, and other measures appropriate for the management of unstable angina should be taken. Patients should be warned against interruption or discontinuation of therapy without the physician’s advice. Because coronary artery disease is common and may be unrecognized, it may be prudent not to discontinue Lopressor therapy abruptly even in patients treated only for hypertension.

Warnings

Hypertension and Angina

Cardiac Failure: Sympathetic stimulation is a vital component supporting circulatory function in congestive heart failure, and beta blockade carries the potential hazard of further depressing myocardial contractility and precipitating more severe failure.

In Patients Without a History of Cardiac Failure: Continued depression of the myocardium with beta-blocking agents over a period of time can, in some cases, lead to cardiac failure. At the first sign or symptom of impending cardiac failure, fully digitalize patients and/or give a diuretic. The response should be observed closely. If cardiac failure continues, despite adequate digitalization and diuretic therapy, withdraw Lopressor.

Bronchospastic Diseases: PATIENTS WITH BRONCHOSPASTIC DISEASES SHOULD, IN GENERAL, NOT RECEIVE BETA BLOCKERS, including Lopressor. Because of its relative beta-1 selectivity, however, Lopressor may be used with caution in patients with bronchospastic disease who do not respond to, or cannot tolerate, other antihypertensive treatment. Since beta-1 selectivity is not absolute, a beta2-stimulating agent should be administered concomitantly, and the lowest possible dose of Lopressor should be used. In these circumstances it would be prudent initially to administer Lopressor in smaller doses three times daily, instead of larger doses two times daily, to avoid the higher plasma levels associated with the longer dosing interval (see Dosage and Administration).

Major Surgery: Chronically administered beta-blocking therapy should not be routinely withdrawn prior to major surgery; however, the impaired ability of the heart to respond to reflex adrenergic stimuli may augment the risks of general anesthesia and surgical procedures.

Diabetes and Hypoglycemia: Beta blockers may mask tachycardia occurring with hypoglycemia, but other manifestations such as dizziness and sweating may not be significantly affected.

Pheochromocytoma: If Lopressor is used in the setting of pheochromocytoma, it should be given in combination with an alpha blocker, and only after the alpha blocker has been initiated. Administration of beta blockers alone in the setting of pheochromocytoma has been associated with a paradoxical increase in blood pressure due to the attenuation of beta-mediated vasodilatation in skeletal muscle.

Thyrotoxicosis: Beta-adrenergic blockade may mask certain clinical signs (e.g., tachycardia) of hyperthyroidism. Avoid abrupt withdrawal of beta blockade, which might precipitate a thyroid storm.

Myocardial Infarction

Cardiac Failure: Sympathetic stimulation is a vital component supporting circulatory function, and beta blockade carries the potential hazard of depressing myocardial contractility and precipitating or exacerbating minimal cardiac failure.

During treatment with Lopressor, monitor the hemodynamic status of the patient. If heart failure occurs or persists despite appropriate treatment, discontinue Lopressor.

Bradycardia: Lopressor produces a decrease in sinus heart rate in most patients; this decrease is greatest among patients with high initial heart rates and least among patients with low initial heart rates. Acute myocardial infarction (particularly inferior infarction) may in itself produce significant lowering of the sinus rate. If the sinus rate decreases to <40 beats/min, particularly if associated with evidence of lowered cardiac output, atropine (0.25-0.5 mg) should be administered intravenously. If treatment with atropine is not successful, discontinue Lopressor and consider cautious administration of isoproterenol or installation of a cardiac pacemaker.

AV Block: Lopressor slows AV conduction and may produce significant first- (PR interval ≥0.24 sec), second-, or third-degree heart block. Acute myocardial infarction also produces heart block.

If heart block occurs, discontinue Lopressor and administer atropine (0.25-0.5 mg) intravenously. If treatment with atropine is not successful, consider administration of isoproterenol or installation of a cardiac pacemaker.

Hypotension: If hypotension (systolic blood pressure ≤90 mmHg) occurs, discontinue Lopressor, and assess the hemodynamic status of the patient and the extent of myocardial damage. Invasive monitoring of central venous, pulmonary capillary wedge, and arterial pressures may be required. Institute appropriate therapy with fluids, positive inotropic agents, balloon counterpulsation, or other treatment modalities. If hypotension is associated with sinus bradycardia or AV block, direct treatment at reversing these (see above).

Precautions

General

Start at a low dose and uptitrate slowly in patients with impaired hepatic function.

Information for Patients

Advise patients to take Lopressor regularly and continuously, as directed, with or immediately following meals. If a dose should be missed, the patient should take only the next scheduled dose (without doubling it). Patients should not discontinue Lopressor without consulting the physician.

Advise patients to:

• Avoid operating automobiles and machinery or engaging in other tasks requiring alertness until the patient’s response to therapy with Lopressor has been determined.

• Contact the physician if any difficulty in breathing occurs.

• Inform the physician or dentist before any type of surgery that he or she is taking Lopressor.

Drug Interactions

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.

Carcinogenesis, Mutagenesis, Impairment of Fertility

Long-term studies in animals have been conducted to evaluate carcinogenic potential. In a 2-year study in rats at three oral dosage levels of up to 800 mg/kg per day, there was no increase in the development of spontaneously occurring benign or malignant neoplasms of any type. The only histologic changes that appeared to be drug related were an increased incidence of generally mild focal accumulation of foamy [[macrophages in pulmonary alveoli and a slight increase in biliary hyperplasia. In a 21-month study in Swiss albino mice at three oral dosage levels of up to 750 mg/kg per day, benign lung tumors (small adenomas) occurred more frequently in female mice receiving the highest dose than in untreated control animals. There was no increase in malignant or total (benign plus malignant) lung tumors, or in the overall incidence of tumors or malignant tumors. This 21-month study was repeated in CD-1 mice, and no statistically or biologically significant differences were observed between treated and control mice of either sex for any type of tumor.

All mutagenicity tests performed (a dominant lethal study in mice, chromosome studies in somatic cells, a Salmonella/mammalian-microsome mutagenicity test, and a nucleus anomaly test in somatic interphase nuclei) were negative.

Reproduction toxicity studies in mice, rats and rabbits did not indicate teratogenic potential for metoprolol tartrate. Embryotoxicity and/or fetotoxicity in rats and rabbits were noted starting at doses of 50 mg/kg in rats and 25 mg/kg in rabbits, as demonstrated by increases in preimplantation loss, decreases in the number of viable fetuses per dose, and/or decreases in neonatal survival. High doses were associated with some maternal toxicity, and growth delay of the offspring in utero, which was reflected in minimally lower weights at birth. The oral NOAELs for embryo-fetal development in mice, rats, and rabbits were considered to be 25, 200, and 12.5 mg/kg. This corresponds to dose levels that are approximately 0.3, 4, and 0.5 times, respectively, when based on surface area, the maximum human oral dose (8 mg/kg/day) of metoprolol tartrate. Metoprolol tartrate has been associated with reversible adverse effects on spermatogenesis starting at oral dose levels of 3.5 mg/kg in rats (a dose that is only 0.1-times the human dose, when based on surface area), although other studies have shown no effect of metoprolol tartrate on reproductive performance in male rats.

References

Adapted from the FDA Package Insert.