Beta Blockers

Beta blockers, also known as beta-adrenergic blocking agents, are drugs that block norepinephrine and epinephrine (adrenaline) from binding to beta receptors on nerves.

Norepinephrine and epinephrine are produced by nerves throughout the body as well as by the adrenal gland. They serve as neurotransmitters (chemicals that nerves use to communicate with one another) that may be active locally where they are produced, or elsewhere in the body, when they are released into the blood. There are both alpha and beta receptors in the body.

3 types of beta receptors

There are three types of beta receptors and they control several different functions based on their location in the body.

1. beta-1 (β1) receptors are located in the heart, eye, and kidneys.
2. beta (β2) receptors are found in the lungs, gastrointestinal tract, liver, uterus, blood vessels, and skeletal muscle.
3. beta (β3) receptors are located in fat cells.

Beta blockers primarily block β1 and β2 receptors and thereby the effects of norepinephrine and epinephrine. By blocking the effects of norepinephrine and epinephrine, beta blockers reduce heart rate; reduce blood pressure by dilating blood vessels; and may constrict air passages by stimulating the muscles that surround the air passages to contract considered an adverse side effect).

Beta blockers are used for treating:

• Abnormal heart rhythms
• High blood pressure
• Heart failure
• Angina (heart pain)
• Tremor
• Pheochromocytoma
• Prevention of migraines
• Hypertrophic subaortic stenosis
• They also have been found to prevent further heart attacks and death after a heart attack.
• Other uses include the treatment of hyperthyroidism, akathisia (restlessness or inability to sit still), panic disorder, anxiety, and aggressive behavior.
• Some beta blockers reduce the production of aqueous humor in the eye and therefore are used for reducing pressure in the eye caused by glaucoma.

Beta blockers may cause:

• Diarrhea
• Stomach cramps
• Nausea
• Vomiting

Other important side effects include:

• Rash
• Blurred vision
• Disorientation
• Insomnia
• Hair loss
• Weakness
• Muscle cramps
• Fatigue

As an extension of their beneficial effect, they slow heart rate and reduce blood pressure, but they may cause adverse effects such as heart failure or heart block in patients with heart problems.

Beta blockers should not be withdrawn suddenly because sudden withdrawal may worsen angina (chest pain) and cause heart attacks, serious abnormal heart rhythms, or sudden death.

• Central nervous system effects of beta blockers include:
  • Headache
  • Depression
  • Confusion
  • Dizziness
  • Nightmares
  • Hallucinations

Beta blockers that block β2 receptors may cause shortness of breath in asthmatics.

As with other drugs used for treating high blood pressure, sexual dysfunction may occur.

Beta blockers may cause low or high blood glucose and mask the symptoms of low blood glucose (hypoglycemia) in people with diabetes.

Other serious side effects of beta-blockers include:

• Toxic epidermal necrolysis
• Raynaud's phenomenon
• Lupus erythematosus
• Bronchospasm
• Serious allergic reactions
• Erythema multiform
• Steven Johnson Syndrome
• Toxic epidermal necrolysis

• acebutolol (Sectral)
• atenolol (Tenormin)
• betaxolol (Kerlone)
• betaxolol (Betoptic S)
• bisoprolol fumarate (Zebeta)
• carteolol (Cartrol, discontinued)
• carvedilol (Coreg)
• esmolol (Brevibloc)
• labetalol (Trandate [Normodyne - discontinued])
• metoprolol (Lopressor, Toprol XL)
• nadolol (Corgard)
• nebivolol (Bystolic)
• penbutolol (Levatol)
• pindolol (Visken, discontinued)
• propranolol (Hemangeol, Inderal LA, Inderal XL, InnoPran XL)
• sotalol (Betapace, Sorine)
• timolol (Blocadren, discontinued)
• timolol ophthalmic solution (Timoptic, Betimol, Istalol)

Beta blockers differ in the type of beta receptors they block and, therefore, their effects.

• Non-selective beta blockers, for example, propranolol (Inderal), block β1 and β2 receptors and, therefore, affect the heart, blood vessels, and air passages.
• Selective beta blockers, for example, metoprolol (Lopressor, Toprol XL) primarily block β1 receptors and, therefore, mostly affect the heart and do not affect air passages.
• Some beta blockers, for example, pindolol (Visken) have intrinsic sympathomimetic activity (ISA), which means they mimic the effects of epinephrine and norepinephrine and can cause an increase in blood pressure and heart rate. Beta blockers with ISA have smaller effects on heart rate than agents that do not have ISA.
• Labetalol (Normodyne, Trandate) and carvedilol (Coreg) block beta and alpha-1 receptors. Blocking alpha receptors adds to the blood vessel dilating effect of labetalol and carvedilol.

• Combining propranolol (Inderal) or pindolol (Visken) with thioridazine (Mellaril) or chlorpromazine (Thorazine) may result in low blood pressure (hypotension) and abnormal heart rhythms because the drugs interfere with each other's elimination and result in increased levels of the drugs.
• Dangerous elevations in blood pressure may occur when clonidine (Catapres) is combined with a beta blocker, or when clonidine or beta blocker is discontinued after their concurrent use. Blood pressure should be closely monitored after initiation or discontinuation of clonidine or a beta blocker when they have been used together.
• Phenobarbital and similar agents may increase the breakdown and reduce blood levels of propanolol (Inderal) or metoprolol (Lopressor, Toprol XL). This may reduce effectiveness of the beta blocker.
• Aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) (for example, ibuprofen) may counteract the blood pressure reducing effects of beta blockers by reducing the effects of prostaglandins, which play a role in control of blood pressure.
• Beta blockers may prolong hypoglycemia (low blood sugar) and mask symptoms of hypoglycemia in diabetics who are taking insulin or other diabetic medications.