Beta Blockers; Types, Indications/Uses, Side Effects, Drug Interactions

Beta blockers








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Beta blockers also written β-blockers, are a class of medications that are particularly used to manage abnormal heart rhythms, and to protect the heart from a second heart attack (myocardial infarction) after a first heart attack (secondary prevention). They are also widely used to treat high blood pressure (hypertension), although they are no longer the first choice for initial treatment of most patients

Beta blockers inhibit the chronotropic, inotropic, and vasoconstrictor responses to the catecholamines, epinephrine, and norepinephrine. Most beta blockers have half-lives of over 6 hours. The shortest actings are pindolol (3 to 4 hours) and propranolol (3 to 5 hours). Most of the included beta blockers are metabolized in combination by the liver and kidneys, with the exception of atenolol, which is metabolized primarily by the kidneys while the liver has little to no involvement.

Classifications/Types of Beta-blockers

α1-receptor antagonism

Some beta blockers (e.g., labetalol and carvedilol) exhibit mixed antagonism of both β- and α1-adrenergic receptors, which provides additional arteriolar vasodilating action.

Dichloroisoprenaline, the first beta blocker

Nonselective agents

Nonselective beta-blockers display both β1 and β2 antagonism.

  • Propranolol
  • Bucindolol (has additional α1-blocking activity)
  • Carteolol
  • Carvedilol (has additional α1-blocking activity)
  • Labetalol (has additional α1-blocking activity)
  • Nadolol
  • Oxprenolol (has intrinsic sympathomimetic activity)
  • Penbutolol (has intrinsic sympathomimetic activity)
  • Pindolol (has intrinsic sympathomimetic activity)
  • Sotalol (not considered a “typical beta blocker”)
  • Timolol

β1-selective agents

β1-selective beta blockers are also known as cardioselective beta blockers.

  • Acebutolol (has intrinsic sympathomimetic activity, ISA)
  • Atenolol
  • Betaxolol
  • Bisoprolol
  • Celiprolol (has intrinsic sympathomimetic activity)
  • Metoprolol
  • Nebivolol
  • Esmolol

β2-selective agents

  • Butaxamine

Classification of overall

Pharmacological differences of Beta-blockers

Agents with intrinsic sympathomimetic action (ISA)

  • Acebutolol, pindolol, labetalol, mepindolol, oxprenolol, celiprolol, penbutolol

Agents organized by lipid solubility (lipophilicity)

  • High lipophilicity: propranolol, labetalol
  • Intermediate lipophilicity: metoprolol, bisoprolol, carvedilol, acebutolol, timolol, pindolol
  • Low lipophilicity (also known as hydrophilic beta-blockers): atenolol, nadolol, and sotalol

Agents with membrane stabilizing the effect

  • Carvedilol, propranolol > oxprenolol > labetalol, metoprolol, timolol

Indication differences of Beta-blockers

Agents specifically labeled for cardiac arrhythmia

  • Esmolol, sotalol, landiolol (Japan)

Agents specifically labeled for congestive heart failure

  • Carvedilol, sustained-release metoprolol

Agents specifically labeled for glaucoma

  • Betaxolol, carteolol, levobunolol, timolol, metipranolol

Agents specifically labeled for myocardial infarction

  • Atenolol, metoprolol (immediate release), propranolol (immediate release), timolol, carvedilol (after left ventricular dysfunction)

Agents specifically labeled for migraine prophylaxis

  • Timolol, propranolol

Propranolol is the only agent indicated for the control of tremor, portal hypertension, and esophageal variceal bleeding, and used in conjunction with α-blocker therapy in phaeochromocytoma.

Mechanism of action of Beta-blockers

Beta-blockers compete with sympathomimetic neurotransmitters such as catecholamines for binding at beta(1)-adrenergic receptors in the heart, inhibiting sympathetic stimulation. This results in a reduction in resting heart rate, cardiac output, systolic and diastolic blood pressure, and reflex orthostatic hypotension.

Beta blockers are classified as a non-cardioselective sympatholytic beta blocker that crosses the blood-brain barrier. It is lipid soluble and also has sodium channel blocking effects. Beta blockers are a non-selective beta blocker; that is, it blocks the action of epinephrine (adrenaline) and norepinephrine (noradrenaline) at both β1– and β2-adrenergic receptors. It has little intrinsic sympathomimetic activity but has strong membrane stabilizing activity (only at high blood concentrations, e.g. overdose). Beta blockers are able to cross the blood-brain barrier and exert effects in the central nervous system in addition to its peripheral activity.

In addition to blockade of adrenergic receptors, beta blockers have very weak inhibitory effects on the norepinephrine transporter and/or weakly stimulates norepinephrine release (i.e., the concentration of norepinephrine is increased in the synapse). Since beta blockers blocks β-adrenoceptors, the increase in synaptic norepinephrine only results in α-adrenoceptor activation, with the α1-adrenoceptor being particularly important for effects observed in animal models. Therefore, it can be looked upon as a weak indirect α1-adrenoceptor agonist in addition to the potent β-adrenoceptor antagonist. In addition to its effects on the adrenergic system, there is evidence that indicates that Beta-blockers may act as a weak antagonist of certain serotonin receptors, namely the 5-HT1A, 5-HT1B, and 5-HT2Breceptors. The latter may be involved in the effectiveness of beta-blockers in the treatment of a migraine at high doses

Indication /Uses of Beta Blockers

Indications for beta blockers include

  • Angina pectoris(contraindicated for Prinzmetal’s angina)
  • Atrial fibrillation
  • Cardiac arrhythmia
  • Congestive heart failure
  • Essential tremor
  • Glaucoma (As eye drops, they decrease intraocular pressure by lowering aqueous humor secretion.
  • Hypertension, although they are generally not preferred as an initial treatment.
  • Migraine prophylaxis
  • Mitral valve prolapse
  • Myocardial infarction
  • Phaeochromocytoma, in conjunction with α-blocker
  • Postural orthostatic tachycardia syndrome
  • Symptomatic control (tachycardia, tremor) in anxiety and hyperthyroidism
  • Theophylline overdose

Beta blockers have also been used for:

  • Acute aortic dissection
  • Hypertrophic obstructive cardiomyopathy
  • Long QT syndrome
  • Marfan syndrome (treatment with propranolol slows progression of aortic dilation and its complications)
  • Prevention of variceal bleeding in portal hypertension
  • Possible mitigation of hyperhidrosis
  • Social and other anxiety disorders
  • Controversially, for reduction of perioperative mortality

Contra-Indications of Beta Blockers

Allergies to

  • Beta-Blockers (Beta-Adrenergic Blocking Agents)

Side Effects

The most common

More common

Rare

Drug Interactions of Beta-blockers

Beta blockers may interact with the following drug, supplyments, & may change the efficacy of the drug

References

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