From metoprolol to carvedilol – how beta-blockers work

Last Updated on October 19, 2021 by Dr.Derek Fhisher

So-called beta-adrenoreceptor antagonists, beta-blockers for short, have become indispensable in modern medicine. They play a central role in the therapy of a wide range of heart conditions, such as heart failure, but can also be used against high blood pressure. To learn how these drugs work, what side effects they have and why you shouldn’t stop taking them, check out our blog today.

Metoprolol, bisoprolol, and carvedilol are probably the best examples among beta-blockers. What they have in common is their blocking effect on so-called β (beta) adrenoreceptors, which are usually activated by the stress hormones adrenaline and noradrenaline. These hormones trigger what are called “response “fight or flight”, which prepares us for stressful situations. They increase blood pressure, heart rate, and heart force. But if the receptors through which these hormones act are blocked, this has the opposite effect: there is a decrease in heart rate, blood pressure and cramps.

The therapeutic indications for the use of beta-blockers can also be deduced from the above effects:

• Coronary heart disease: lowering heart rate improves blood flow to the coronary arteries because the heart goes through a longer diastole (the relaxation and filling phase of the heart), in which blood flow occurs.
• Cardiac arrhythmias: in addition to numerous other drugs, beta-blockers can also be used to regulate rhythm. They prevent overexcitation of the heart muscle.
• Heart failure: Stress hormone blockade leads to more economical heart function and therefore relief.
• High blood pressure: beta-blockers have also proven themselves in the treatment of arterial hypertension. However, they are not usually the drugs of first choice, but should only be used when other drugs, such as ACE inhibitors or diuretics, fail to achieve the desired effect.
• Others: beta-blockers also interfere with other organs because of their complex mechanism of action control loops in the body and have beneficial effects there. They can be used to prevent migraines, glaucoma, hyperthyroidism, and even anxiety disorders.

As the famous German pharmacologist Gustav Kuszczynski said, there is probably not a single substance with a therapeutic effect without side effects. In general, beta-blockers are very well tolerated when taken long-term. The most important side effects are bradycardia (pulse too slow), fatigue, erectile dysfunction, exacerbation of minor circulatory disorders, weight gain, and depressed mood. Particular caution should be exercised by asthmatics. Activating β2 receptors, stress hormones lead to bronchial dilation, which helps us breathe better in stressful situations. If we block it, the bronchi cannot expand properly. Non-asthmatics can compensate for this, asthmatics cannot. Therefore, beta-blockers should not be used in asthma!

Dosage Notes

Finally, two very important notes on beta-blocker dosing: you must always have a crawling attack. That is, the dose is gradually increased until the desired dose is reached. This is especially important in cases of heart failure, since the reduction in shock force caused by beta-blockers can itself lead to inadequate pumping power. With a competent approach, this risk is minimized by creeping dosing.

It is equally important that you never stop taking beta-blockers on your own. Abrupt discontinuation of the drug can lead to so-called “rebound phenomenon”. When blocking β-receptors, special regulatory mechanisms lead to an increase in receptor density. If the blockade disappears, the receptors become too many, and an excessive stress response from adrenaline and noradrenaline occurs. In the worst case, it can lead to cardiac arrhythmia, heart attack, or sudden cardiac death. Therefore, if for any reason you want to stop taking a beta-blocker, please consult your doctor beforehand.