Beta blockers are a class of medicines that are administered in the treatment of several medical conditions. I present to you a comprehensive article on the types of beta blockers, their mechanism of action, indications, contraindications and side effects.
Beta blockers commonly used in the treatment of various illnesses including high blood pressure, migraine, angina, cardiac arrhythmias, myocardial infarctions and pheochromocytoma. These drugs are used for cardioprotection. They also play an important role in the prevention of heart-related ailments. Due to their various uses, it is imperative that we try to understand more about these highly useful drugs. The use of beta blockers became popular when in 1962, Sir James W. Black found the applications of propranolol and pronethalol in the treatment of angina pectoris. Given below is an exhaustive list of beta blockers and descriptions of the different functions they perform:
Propranolol is considered the prototype in beta blockers. It was introduced in 1963, and was considered a huge breakthrough drug. It is a non-selective beta blocker. Although it competitively blocks both β1 and β2, it has weak activity on β3 receptors. Apart from being non-selective in nature, propranolol also exhibits membrane stabilizing activity.
Effects of Propranolol: Being a non-selective beta blocker, propranolol acts on all β receptors present in our body, thus bringing about the following effects:
- Heart: Propranolol decreases the heart rate, force of contraction and also the cardiac output. It tends to prolong the systolic phase by retarding conduction in the myocardium.
- Respiratory tract: Propranolol increases the bronchial resistance by blocking β2 receptors. This effect is hardly discernible in normal individuals because the sympathetic bronchodilator tone is minimal.
- Central Nervous System: Propranolol is known to suppress anxiety in short-term stressful situations, although this is brought about more due to its peripheral activity rather than central activity.
- Local anesthetic: Propranolol can act as a potent anesthetic when used as lidocaine, but it is not used because of its irritant property.
- Metabolic effects: Though propranolol does not have any effect on blood sugar level, its prolonged use may reduce carbohydrate tolerance by decreasing the release of insulin.
- Skeletal muscle: Propranolol is known to decrease the adrenergically provoked tremors. This is a peripheral action directly exerted on muscles.
- Eye: Propranolol, along with certain other β blockers, reduces the secretion of aqueous humor, thus, lowering the intra-ocular tension.
Indications: Owing to the multiple beta blocker effects that propranolol has on the sympathetic system, this prototype drug is used for treating several heart diseases.
- Hypertension: Propranolol is a commonly used hypertension medication, although it has a relatively mild antihypertensive activity; this is because it has good patient acceptability.
- Angina pectoris: Angina pectoris is a condition where, due to transient hypoxia of the heart muscle, a person experiences severe chest pain. This hypoxic condition occurs due to narrowing of coronary arteries. Propranolol is used in treating angina, as it decreases the workload of heart. If taken on a regular basis, it decreases the frequency of attacks.
- Myocardial infarction: Propranolol is also given to patients who have suffered from a myocardial infarction i.e. heart attack. They are used as a secondary prophylaxis of myocardial infarction, because they prevent re-infarction and sudden ventricular fibrillation at the second attack.
- Stress and Anxiety: One of the frequently used beta blockers for treatment of anxiety, propranolol blocks the sympathetic nerves, thereby inhibiting the peripheral manifestations of stress and anxiety.
- Tremors: Being a non-selective β blocker, propranolol helps in treating essential involuntary rhythmic tremors. However, it does not help in treating parkinsonian tremor.
- Pheochromocytoma: β blockers like propranolol maybe used to control tachycardia and arrhythmia; however, they should only be used after an α blocker has been administered, or else the blood pressure shoots up dangerously.
- Migraine: Propranolol is the most effective drug for chronic prophylaxis of migraine, as it reduces the frequency and severity of attacks in almost 70% of the patients. The effect is generally observed in four weeks and sustained during prolonged therapy.
- Thyrotoxicosis: Propranolol rapidly controls the symptoms associated with hyperthyroidism (like palpitations, sweating, tremors etc.) without significantly altering the thyroid status. It is especially used post-operatively while awaiting response to antithyroid drugs or radioactive iodine.
- Cardiac Arrythmias: The β blockers like propranolol suppress extrasystoles and tachycardias, especially those that are mediated adrenergically. Propranolol helps control the ventricular rate in atrial fibrillation and flutter, but only occasionally restores the sinus rhythm.
Contraindications: Some of the effects produced by propranolol maybe harmful for people suffering from specific diseases. These diseases include the following:
- Congestive Cardiac Failure: Due to its action of blockage of sympathetic support to the heart, propranolol can precipitate edema and thus, congestive heart failure, especially while experiencing cardiovascular stress.
- Asthma: Propranolol is contraindicated in cases of asthma because it tends to increase the bronchial resistance by means of blocking the β2 receptors, which consistently worsen asthma and, which may even precipitate a severe asthma attack. It also known to worsen the chronic obstructive lung disease.
- Heart block: In cases of complete or partial heart block, propranolol is strictly contraindicated as it may lead to a cardiac arrest.
- Corornary artery disease: Propranolol has the effect of altering lipid profiles by causing an increase in the LDL-cholesterol and a decrease in HDL-cholesterol. This precipitates the condition of coronary heart disease
Side effects: Most beta blocker side effects are mild because the drugs are quite well tolerated. However, here are few of the side effects of propranolol:
- It is known to accentuate myocardial insufficiency.
- It may bring about bradycardia (decreased heart rate).
- It worsens the chronic obstructive lung disease
- It may impair the carbohydrate tolerance in borderline diabetics
- It alters the plasma lipid profile on prolonged use
- It may lead to cold hands and feet and the worsening of peripheral vascular disease
- It may lead to lethargy, excessive fatigue and a decreased capacity for exercise.
Sotalol is a drug that figures in the list of non-selective category. It does not show any kind of intrinsic sympathomimetic activity and does not block the alpha receptors. Sotalol is one of the unique drugs as it not only shows activity on beta receptors, but also blocks the potassium channels in the heart. It is therefore, used in the treatment of atrial fibrillation and other life-threatening ventricular arrhythmias; it helps return the heartbeat to a normal rhythm and reduces the risk factors considerably. This drug is normally avoided in children and pregnant women, as there isn’t enough data to prove their safety in such individuals. Sotalol is strictly contraindicated in nursing mothers, because it can pass through into breast milk in significant amounts, thereby posing a risk to infants. Sotalol also is contraindicated in patients with kidney diseases.
There are certain risks associated with sotalol. This drug should be used only if absolutely necessary, in arrhythmia cases. ECG monitoring is required for three days after a steady sotalol dosage has been reached, as this medicine can initially cause irregular heartbeats. Sotalol is contraindicated in diseases (like diarrhea) which disturb the electrolyte balance of the body, as low electrolyte levels may increase the risk of arrhythmias. Furthermore, sotalol interacts with many drugs which include calcium channel blockers, antacids and certain diuretics, among others. An overdose of sotalol can lead to dangerously low blood pressure.
Sotalol may cause drowsiness, dizziness and a feeling of being light-headed.
The first generation non-selective beta blockers, timolol is also used in the treatment of hypertension, angina, heart attacks, migraine and headaches. Like propranolol, it decreases the heart rate, thus, decreasing the systolic and diastolic pressure. It is relatively well tolerated, with very mild side effects like nausea and cold hands and feet. It is to be used in pregnant ladies or nursing mothers only if necessary. Timolol is occasionally given for treating anxiety. A special use of timolol can be found in glaucoma and other eye conditions. It reduces the pressure in the eyes when used as eye drops on a regular basis. The medication may initially lead to a slight stinging or burning sensation, but this normally subsides after regular use. If this kind of stinging persists, or if pain develops, then one should discontinue the use of medication and consult an ophthalmologist immediately.
Timolol interacts with drugs like calcium channel blockers and clonidine.
Amongst the few beta blockers drugs which exhibit prominent intrinsic sympathomimetic activity, pindolol is primarily used as an anti-hypertensive. It is especially given to patients who develop marked bradycardia on prolonged use of propranolol. Another advantage of using this drug is that the rebound hypertension symptoms on withdrawal are less. Additionally, the effective dose range is quite narrow.
This drug has relatively few side effects and is quite well tolerated. However, it is contraindicated in kidney disease patients and it can show severe withdrawal symptoms if abruptly stopped. Ironically, while the beta blockers are mostly used in cases of heart failure, pindolol and certain other such drugs can worsen heart failure in some instances. The prolonged use of pindolol and other non-selective beta blockers can lead to the masking of symptoms of hypoglycemia (low blood sugar level). This can turn out to be quite problematic in diabetics. This drug is contraindicated in nursing mothers.
Atenolol prominently figures on the list of cardioselective beta blockers. It is a β1 blocker that has low lipid solubility. It is not completely absorbed, orally. However, due to its longer duration of action, a single daily dose is often sufficient. Lesser side effects are observed when related to the central nervous system. Also, the lipid profiles aren’t significantly altered, thus, it is not dangerous to use even in people with coronary artery disease. However, in the patients suffering from coronary artery disease, stopping the administration of atenolol abruptly can worsen angina symptoms, which may even precipitate heart attacks. Also, atenolol is one of the most commonly used drugs for hypertension, as it brings about lowering of high blood pressure and angina. Atenolol is also helpful in treating tachycardias (very fast heart rate) in myocardial infarctions, migraine and tremors.
Atenolol comes in tablet form, and it can be taken either before meals or at night. However, this drug should not be prescribed with calcium channel blockers, as synergistically they can drastically bring down the blood pressure and heart rate to dangerous levels.
Atenolol is contraindicated in pregnancy as it may harm the fetus and cause growth retardation. The side effects of atenolol are similar to the side effects caused by drugs that come under this category.
This is also a cardioselective beta blocker with marked partial agnostic and membrane stabilizing properties. It has a relatively lesser effect on the heart rate. The side effects observed are similar to those seen in metoprolol. Due to its long half-life, a single dose of acebutolol suffices for most patients.
Due to its cardioselective activity, it is the preferred beta blocker in asthmatics and chronic obstructive pulmonary disease (COPD) patients. Acebutolol is available in capsule form, and is normally taken with a meal; it can also be taken on an empty stomach. Acebutolol is used alone or in combination with other drugs for treating hypertension and arrhythmias. It is also used in the treatment of angina pectoris. Side effects of this drug include fatigue, dizziness and headaches.
Metoprolol is considered as the prototype in cardioselective beta blockers. It acts on the β1 receptors. Its potency to block cardiac stimulation is similar to that of propranolol. Although metoprolol is relatively less likely to worsen asthma, it is still not safe for asthmatics. It is also the preferred drug in people suffering from diabetes. Also, patients complaining of cold hands and feet while on propranolol often respond well to metoprolol. The side effects of metaprolol are mild. It is generally given orally, though in severe cases of myocardial infarction it can also be given intravenously. It is also available in an extended release version. Metoprolol should be taken either with a meal, or immediately after a meal.
Metoprolol reverses the effects of stress hormones, thus it is one of the recommended drugs for anxiety treatment. However, it can significantly precipitate asthma. It is not used for treating children, and like most drugs under this category, is contraindicated in nursing mothers.
This drug is strictly cardioselective in action. It lacks the intrinsic sympathomimetic activity and is thus, suitable for daily administration in patients suffering from hypertension and angina. The mechanism of action and side effects of this drug are similar in nature to those found in acebutolol. Bisoprolol is available in tablet form and is to be taken once a day, with a meal or on an empty stomach. Incidentally, this is the only beta blocker being used in the treatment of congestive heart failure. The dose will depend on the severity of hypertension and on how well the patient responds to this drug. Potency of this drug can get hampered if it is given in combination with NSAIDs (non-steroidal anti-inflammatory drugs) like ibuprofen.
One of the important drugs in the cardioselective category, esmolol is an ultra-short acting β1 blocker, devoid of partial agnostic or membrane stabilizing activity. The plasma half life is less than ten minutes, as it is inactivated by esterates in the blood. Its action lasts for 15-20 minutes after the termination of intravenous infusion. Thus, it has a rapid onset of action, with a short lasting but almost instantaneous fall in blood pressure. Esmolol has been used to terminate supraventricular tachycardia, arrhythmia during anesthesia, episodic atrial fibrillation (to reduce heart rate and blood pressure during and after a cardiac surgery) and in early treatment of myocardial infarction. Thus, it is used only for temporary treatment. Also, because medication is given in intravenous mode, care has to be taken to ensure that there is no leakage of drug into the veins, as this may be injurious to health. Esmolol may cause low blood pressure, nausea and dizziness.
Labetolol hydrochloride, along with carvedilol acts on both, alpha and beta receptors. This is possible because there are four stereoisomers of labetolol, each of which has a distinct profile of action on subtypes of α and β receptors. However, labetolol is five times more capable of blocking β than α receptors. The effects that are observed, resemble the ones resulting from low dose propranolol. Fall in blood pressure (both systolic and diastolic) occurs due to α1 and β1 blockade as well as β2 agonism (vasodilation). High doses however, reduce cardiac output. One of the ways in which it differs from propranolol is that, limb blood flow increases with labetolol. Some of the major indications of labetolol include pheochromocytoma, clonidine withdrawal and essential hypertension. One of the major side effects of labetolol is that it causes postural hypotension. This beta blocker is used for controlling high blood pressure, although it is not a cure for it.
Carvedilol has an action on β1, β2 and α1 adrenoreceptors. It brings about vasodilation due to α1 blockade. It also has an antioxidant property. It is mainly used in hypertension, and is the β blocker especially employed as a cardioprotective in congestive heart failure. It has a half-life of 2 – 8 hours. Carvedilol comes in tablet form and it has to be taken twice in a day, preferably with food. It should be taken at the same time everyday, to maintain an even level in the blood. Also, the drug should not be abruptly withdrawn, as it can lead to side effects, which may lead to dire consequences.
This was an exhaustive beta blockers list. Discovery of these drugs is truly a landmark in the field of pharmacology, since they are used in the treatment of various ailments. So take full advantage of these drugs, as they are considered to be miracle drugs for hypertensives and other heart patients.
Disclaimer: The information provided in this article is solely for educating the reader. It is not intended to be a substitute for the advice of a medical expert.