How metoprolol works
Metoprolol is a drug from the group of beta-1-selective beta-blockers (beta-1 receptors are found primarily in the heart). It lowers the heart rate (negative chronotropic), reduces the beating force of the heart (negative inotropic) and influences the conduction of excitation (negative dromotropic; antiarrhythmic effect).
In sum, the heart has to work less and less oxygen is consumed – the heart is unburdened. Furthermore, metoprolol has a blood pressure-lowering effect, which is exploited in the therapy of high blood pressure (hypertension).
In stressful situations, the body releases the hormone adrenaline into the blood. This stress hormone reaches all the organs of the body via the bloodstream within a very short time and transmits the stress signal by binding to certain receptors (beta-adrenoceptors) in the organs.
The affected organs then adapt their activity to the stress situation – the bronchi dilate to take in more oxygen, the muscles receive more blood flow, digestive activity is reduced, and the heart beats faster to supply the entire body with more oxygen and energy.
The active ingredient metoprolol very selectively blocks the adrenaline binding sites (syn. beta receptors) on the heart so that the stress hormone can no longer dock there and exert its effect – the heartbeat remains at a normal level.
Absorption, degradation and excretion
Metoprolol taken by mouth (orally) is almost completely absorbed in the intestine, but then about two-thirds of it is broken down by the liver before it reaches its site of action.
Since the active ingredient is excreted comparatively quickly (reduction by about half after three to five hours), retard tablets or capsules are often used, which release the metoprolol with a delay. In this way, the active ingredient levels in the body remain more or less the same throughout the day and the drug only needs to be taken once a day.
When is metoprolol used?
The active ingredient metoprolol is approved for the treatment of:
- High blood pressure
- coronary heart disease with angina pectoris
- Cardiac arrhythmias
- long-term treatment after a heart attack
- stable chronic cardiac insufficiency (heart failure)
Rather atypical seems the use of metoprolol for the prevention of migraine attacks. However, by regulating blood pressure, the drug may reduce the frequency and severity of attacks.
How metoprolol is used
The active ingredient metoprolol is used in the form of its salt with succinic acid (as succinate, “metoprolol succ.”), with tartaric acid (as tartrate), or with fumaric acid (as fumarate).
The most common dosage forms are tablets with delayed release of the active ingredient (retard tablets). There are also normal tablets and injection solutions.
Also available are combination preparations that contain a diuretic or a calcium channel blocker in addition to metoprolol. Patients with high blood pressure often have to take these agents as well, so combining them in one tablet makes it easier to take the medication.
Retard tablets usually need to be taken only once a day, while immediate-release tablets need to be taken several times a day. The physician determines the optimal metoprolol dosage for the patient.
If metoprolol is to be discontinued, this should be done slowly and by gradually reducing the dose. Otherwise, a so-called “rebound phenomenon” may occur, whereby blood pressure reflexively skyrockets after discontinuation of the drug.
Never stop treatment with metoprolol abruptly. The dose must be reduced slowly over a long period of time.
What are the side effects of metoprolol?
Rare side effects (in one to ten treated people out of 10,000) include nervousness, anxiety, decreased lacrimation, dry mouth, hair loss, and impotence.
What should be considered when taking metoprolol?
Contraindications
Metoprolol should not be used in:
- AV block of the II. or III. degree
- certain forms of cardiac arrhythmia
- bradycardia (slow heartbeat below 50 beats per minute)
- hypotension (low blood pressure <90/50mmHg)
- concomitant administration of monoamine oxidase inhibitors (MAO inhibitors)
- severe bronchial disease (e.g., uncontrolled bronchial asthma)
Interactions
The active ingredient metoprolol is broken down in the liver by a frequently used metabolic pathway by which many other drugs are also metabolized. As a result, metoprolol can interact with a variety of other drugs/groups of drugs:
- Antidepressants such as fluoxetine, paroxetine, and bupropion.
- Anti-arrhythmic drugs (antiarrhythmics such as quinidine and propafenone)
- Allergy medications (antihistamines such as diphenhydramine)
- antifungal drugs (such as terbinafine)
Because other medicines may also interact with metoprolol, the doctor will ask what other medicines you are taking before prescribing.
Age Limit
Pregnancy and lactation
Metoprolol is one of the antihypertensives of choice for pregnancy. With prolonged use, the growth of the unborn child should be monitored because Metoprolol may cause decreased blood flow to the placenta, resulting in insufficient blood supply to the child.
Metoprolol is one of the beta-blockers of choice during breastfeeding. Because it passes into breast milk, attention should be paid to possible side effects in the breastfed infant. In isolated cases, a slowing of the heartbeat (bradycardia) has been observed.
How to obtain medication with metoprolol
Metoprolol is available by prescription in Germany, Austria, and Switzerland in any dosage, and thus only against prescription in pharmacies.
How long has metoprolol been known?
Metoprolol was first marketed as a drug in the form of its tartaric acid salt in the USA in 1978. In the course of extended patent applications, the active ingredient was also developed as succinate and approved in the U.S. in 1992.
In the meantime, numerous low-cost generics containing metoprolol are on the market.
