Beta blockers: what they are, side effects

Beta-blockers are a class of drugs used, under prescription, such as:

  • Antiarrhythmics: they act by preventing or correcting any abnormalities in the rhythm of the heartbeat, that is, alterations in the cadence of electrical and mechanical events that allow the heart to function as a pump;
  • Antihypertensives: act in the control of blood pressure by interfering, at various levels, with the mechanisms that physiologically regulate it to counteract high blood pressure problems ;
  • Antianginal: they act by reducing the symptoms of angina pectoris, a clinical syndrome characterized by pain in the chest and surrounding areas (arms, neck, back, and also jaw), following a reduction in the oxygen supply that reaches the heart.

These drugs exert their action by binding to the β (beta) type receptors for adrenaline and noradrenaline and allow, thanks to the blocking of the effect of these hormones on the heart, a reduction in the force of contraction of the heart and heart rate. In other words, they replace the substances produced by the body that normally stimulate and regulate the heart, counteracting the appearance of the listed ailments.

Moreover, thanks to their inhibitory action of stress hormones, they can also be used in the therapy of anxiety states.

They are generally formulated in the form of tablets and eye drops (the latter limited to the treatment of eye diseases).

Tablets arranged in the shape of a heart, placed on an EKG report

Β-adrenergic receptors

Speaking of living organisms, a receptor is a structure (protein) that can bind to a specific molecule; in the presence of this union, the appearance of a specific biological effect is observed; we can imagine the receptors as a sort of button, useful for activating specific functions within the cells.

There are many types of receptors, but speaking of beta-blocking drugs it is sufficient to focus our attention on the β-adrenergic receptors; There are three different types of β-adrenergic receptors that interact with adrenaline and other catecholamines (noradrenaline, dopamine):

  • Β1: it is the most represented receptor in the heart and kidney, but it is also present in the eye; when activated, this receptor acts by increasing the work of the heart and stimulating the secretion of renin (a proteolytic enzyme released by the kidney in response to factors that reduce blood pressure) in the kidney and aqueous humor in the eye.
  • Β2: is the receptor found at the level of the arteriolar, genitourinary, gastrointestinal and bronchial smooth muscles; if activated, this receptor causes muscle relaxation, with consequent bronchodilation. Β-2 receptors are also found in skeletal muscle, liver and mast cells and are involved in the release of insulin.
  • Β3: is the receptor located in the adipose tissue, where it stimulates lipolysis (the metabolic process that allows the breakdown of triglycerides and the release of fatty acids and glycerol, a source of energy).

Based on the receptor action, β-blocking drugs can be:

  • Non -selective: they do not act exclusively on the heart, but also on beta receptors located in other districts (such as beta-2).
  • Selective: they have a selective antagonist action on beta-1 receptors and exert their effects mainly at the cardiovascular level.

We can also classify them as:

  • First-generation beta-blockers (non-selective): these include timolol, propranolol, and nadolol.
  • Second-generation beta-blockers (selective on beta-1 receptors): include atenolol, metoprolol, acebutolol, and bisoprolol.
  • Third-generation beta-blockers (with enhanced action): in addition to the inhibition mechanism of beta-1 receptors, these drugs enhance (therefore they have an agonist action) the activity of beta-2 receptors (this is the case of celiprolol), or increase the secretion of nitric oxide in the blood vessels, causing vasodilation and enhancing the blood pressure-lowering (hypotensive) effect of the drug (this is the case with nebivolol).
  • Third-generation beta-blockers with additional effects and selective beta-1: they also include beta-blockers with intrinsic sympathetic-mimetic activity (or isa), such as pindolol and acebutolol, used, for the lower depression of cardiac function, especially in bradycardia (patients with decreased heart rate).

What are they for

There are different types of beta-blockers, each characterized as seen by specific properties and therefore useful for the treatment of specific pathologies; from a general point of view they are mainly used in the following pathologies:

  • Arterial hypertension ( high blood pressure ): a clinical condition characterized by high blood pressure in the arterial vessels.
  • Cardiac arrhythmias: alterations in the heart rhythm, for which the beat is irregular, with moments of increase ( tachycardia ), decrease (bradycardia) or absolute irregularity (for example in the case of atrial fibrillation ), compared to the norm.
  • Heart failure: dysfunction as a result of which the heart is no longer able to meet the needs of the body, with a consequent reduction in blood flow and accumulation of the same in the veins and lungs and other alterations that can further decrease heart function.
  • Myocardial infarction (in secondary prevention, i.e. aimed at preventing a further heart attack): event determined by the interruption of blood flow to the heart which, if continued over time, can cause damage or destruction of part of the heart muscle.
  • Thyrotoxicosis: a clinical picture that arises following the exposure of body tissues to the action of thyroid hormones present in excess.
  • Glaucoma: eye disease usually related to too high eye pressure.
  • Essential tremor: movement disorder characterized by a tremor localized mainly in the upper limbs and head, which worsens in states of agitation, nervousness, emotionality, or in particular conditions of anxiety.
  • Migraine (some forms): present with intense, throbbing pain, usually located in the front or side of the head.

Note that they are generally not recommended as first-choice drugs for the treatment of high blood pressure, except in combination with or as an alternative to other drugs (such as diuretics).

Side and unwanted effects

Most patients on beta-blocker therapy do not suffer from any side effects. Or when present they tend to gradually resolve over time.

The side effects associated with taking beta-blockers vary according to the timing. The mode of intake, as well as by virtue of the generation of the drug taken.

The most commonly reported symptoms in clinical trials of the effects of beta-blockers taken by mouth are:

  • Dizziness (described as the feeling that the person or their surroundings are moving or spinning),
  • Tiredness,
  • Blurred vision,
  • Cold hands and feet,
  • Slow heartbeat,
  • Diarrhea,
  • Bronchoconstriction (closing of the bronchi with difficulty in breathing),
  • Acute hypotension (excessive lowering of blood pressure),
  • Nausea.
  • Less common ailments include:
  • Sleep disturbances ( difficulty falling asleep, awakening at night),
  • Excessive fatigue and shortness of breath (for example when climbing stairs),
  • Decreased sexual desire,
  • Difficulty getting or maintaining an erection,
  • Depression ,
  • Increased triglycerides and transaminases in the blood,
  • Jaundice (yellowing of the skin).

It is also important, in the event of a decrease in dosage or interruption of therapy, to gradually reduce the dose of the drug, and to avoid dangerous hypertensive crises, conditions characterized by a sudden and violent increase in blood pressure.

Contraindications

The use of beta-blockers is generally contraindicated in patients with:

  • Pathologies associated with bronchoconstriction, such as asthma, COPD (chronic obstructive pulmonary disease), …,
  • Bradycardia (slow heart rate),
  • Metabolic acidosis,
  • Pathologies characterized by difficulty in limb circulation, such as Raynaud’s syndrome ).
  • In these categories of patients, it is preferable to administer, respectively,
  • Cardioselective beta-blocking drugs
  • And beta-blocker drugs isas,
  • always under medical advice.
  • The contraindication also extends to patients affected by:
  • Diabetes (or in any case undergoing insulin treatment) or hypoglycemic syndromes (characterized by low blood sugar);
  • Liver function disturbances.
  • Pregnancy and breastfeeding

The use of beta-blockers during pregnancy or breastfeeding is generally not recommended, precisely because of the possible side effects.

In any case, the choice of the drug to be adopted is up to the doctor, who will evaluate the most appropriate therapy considering the individual variations and the clinical situation of the individual patient, thus weighing the so-called risk-benefit ratio.

Missed dose

Most beta-blockers are taken once a day, with the exception of some molecules that are used during pregnancy and sotalol, which is given 2 or 3 times a day.

If a dose is missed, it is generally advised to recover it immediately. Unless the next dose is imminent (in this case the missed dose should NOT be recovered by doubling the dose.

However, refer to your doctor if in doubt.

Other warnings

In case of taking a higher dose than the one prescribed. It is necessary to contact a doctor or the emergency room to find out how to intervene, as most beta-blockers are taken in single daily administration; overdose can slow heart rate and make breathing difficult, as well as cause dizziness and tremor.

It should also be remembered that beta-blockers can interfere with the effects of other drugs, modifying their effectiveness; for clarification regarding this eventuality, it is advisable to consult your doctor or pharmacist and read the package leaflet carefully.

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