Metoprolol is a treatment and not a cure for the conditions it is used to treat. It may take a few weeks before you start to notice the benefits of the medication. Certain allergies may exacerbate any reactions to the drug, this can include being unresponsive to epinephrine. If you have asthma, suffer from heart failure or a slow heart rate (bradycardia), beta blocker medications are generally not recommended.
Doctors usually do not prescribe the drug to those who suffer from diabetes or people older than 65. However, this is often dependent on the health status of the person concerned. It is always best to consult with a doctor and discuss the suitability of the medication being prescribed should you have any pre-existing health condition. Full medical history disclosure and current medication use during any medical consultation is always advisable to ensure your safety.
Metoprolol carries an FDA Black Box Warning, the highest possible alert this organisation can issue to a user of the potential dangers of a drug. This warning is issued in regard to the dangers of the sudden discontinuation of Metoprolol which has been reported to worsen chest pain (angina), irregular heartbeat (ventricular arrhythmias) and may increase the risk of a heart attack (myocardial infarction). Beta blocker therapy, especially in those suffering from coronary artery disease (CAD), should be tapered off over a week or two to avoid increased heart rate (tachycardia), high blood pressure (hypertension) and inadequate circulation (ischemia).
Metoprolol warning include:
- Asthma or chronic obstructive pulmonary disease (COPD): It is best not to take metoprolol if you are asthmatic or have other breathing related issues. This is due to the fact that metoprolol is able to block receptors in the breathing passages, narrowing them and worsening any breathing problems you may have.
- Certain heart conditions: If you suffer from one of the following heart-related conditions, a doctor will not prescribe metoprolol:
- A heart rate lower than 45 beats per minute
- A first degree heart block (atrioventricular block) with P-R Intervals of 0.24 sec or greater
- Second or third degree heart blocks (av blocks) unless a working pacemaker is in place
- Pulmonary oedema (excess fluid on the lungs)
- Systolic blood pressure less than 100 mmHg
- Prinzmetal variant angina (also known as vasospastic angina, which is a form of chest pain that occurs while at rest, rather than during exertion as is typical of classic angina)
- Cardiogenic shock
- Acute heart failure (especially in cases of severe left ventricular dysfunction)
- Cerebrovascular disease: Due to its effects on blood pressure and heart rate, doctors will prescribe metoprolol with caution in those with cerebrovascular disease (a group of conditions that affect blood supply to the brain) or who have suffered from a stroke. If blood flow to the brain is compromised after the drug is used, which is usually indicated by signs and symptoms of dizziness, visual disturbances (double vision), difficulty with speech (slurring or garbled speech) and/or falls (drop attacks), an alternative will be prescribed.
- Diabetes: Metoprolol can eliminate tremors and increase heart rate in some, which are both helpful indicators when monitoring low blood sugar. If these signals are not present, it can be more difficult to recognise the signs of low blood sugar, thus making it dangerous for people with diabetes mellitus to take the drug.
- Liver disease: Metoprolol is cleared in the liver, as such, doctors will be cautious of prescribing the drug to those with severely impaired liver function. In cases where this drug is prescribed, dosages will be lowered, especially when extended-release forms of metoprolol are used, and gradually increased to an effective therapeutic level.
- Myasthenia gravis: This condition which causes weakness and fatigue of the muscles may be exacerbated by metoprolol use. Double vision has also been reported due to its use in those with this condition.
- Peripheral vascular disease (PVD) and Raynaud disease: This medication may cause or exacerbate the slowing of blood flow through the arteries (known as arterial insufficiency) associated with these conditions. Metoprolol will be used with caution and your doctor will advise you on the signs and symptoms of arterial blockage to be aware of. These include, amongst others:
- Pain and cramping in the hip or leg (claudication)
- Numbness or weakness of the leg
- Increased sensations of cold in the leg or foot in comparison to the other leg
- Changes in colour of the leg
- Pheochromocytoma: In those with diagnosed or suspected pheochromocytoma (a hormone secreting tumour of the adrenal glands) metoprolol will only be prescribed with an alpha-blocker and should only be taken after alpha-blocker therapy has started to avoid dangerous elevations in blood pressure due to reduced dilation of the blood vessels (vasodilation).
- Poor blood circulation: Having bad circulation in your hands and feet can be worsened by taking metoprolol as the drug decreases blood pressure, resulting in less blood flow to these areas.
- Pregnancy & Breastfeeding: Metoprolol is a category C drug, this means that research conducted on animals has shown negative effects on the foetus when the mother is taking the drug. In addition, it means that there haven't been enough studies conducted on humans to draw conclusive findings on how this drug will affect an unborn child. Metoprolol can enter breast milk and be passed to a baby when breastfeeding, which can be dangerous to the health of the baby.
- Psychiatric disease: It is important to mention any previous diagnoses of psychiatric disease to your doctor (if he/she does not have your full medical history) as metoprolol can cause or worsen Central Nervous System depression.
- Skin Conditions: Metoprolol may cause or worsen skin conditions like psoriasis and eczematous lesions (signs of eczema).
- Seniors: Seniors are often given a smaller dose of metoprolol first, with dosages then increasing gradually.
- Surgery: You should let your doctor know if you are expecting to have surgery, this also includes dental surgery.
- Thyroid disease (hyperthyroidism and thyrotoxicosis): Metoprolol may mask the symptoms of thyroid disease like elevated heart rate (tachycardia) which is useful for monitoring purposes and lead to changes in thyroid function tests. If you have a confirmed thyroid disease, a doctor will prescribe this medication with caution.