Metoprolol

Metoprolol comes in several formulations approved for different conditions — not every form is approved for every use.

• Metoprolol succinate extended-release tablets (including Toprol-XL and generic ER forms): approved for high blood pressure, angina pectoris, and heart failure (stable, symptomatic NYHA Class II or III from ischemic, hypertensive, or cardiomyopathic causes). Toprol-XL is specifically indicated to reduce the risk of cardiovascular death and heart failure hospitalizations.
• Metoprolol tartrate tablets (including Lopressor and generic immediate-release forms): approved for high blood pressure, angina pectoris, and to reduce the risk of cardiovascular death after a definite or suspected heart attack — when used together with intravenous metoprolol in hemodynamically stable patients.
• Metoprolol tartrate injection (intravenous): approved for use in hemodynamically stable patients with a definite or suspected acute heart attack, to reduce cardiovascular death, followed by a transition to oral metoprolol therapy.

Metoprolol works by selectively blocking beta-1 adrenergic receptors — the receptors in the heart that respond to adrenaline (catecholamines). Blocking these receptors slows the heart rate, reduces the strength of each heartbeat, and lowers blood pressure. In angina, this means the heart demands less oxygen during exertion. In heart failure, this beta-blockade appears to help the heart function more efficiently over time, improving the heart's pumping ability (left ventricular ejection fraction).

At higher blood levels, metoprolol's selectivity for heart receptors decreases and it can also affect beta-2 receptors in the lungs and blood vessels — which is why caution is needed in people with asthma or other breathing conditions. The drug also slows conduction through the heart's electrical system (AV node), which can be beneficial but requires monitoring in people with certain rhythm disorders.

How metoprolol is taken depends on the formulation your doctor prescribes.

• Extended-release tablets (succinate): Taken once daily by mouth. Can be taken with or without food. Scored tablets may be split, but do not crush or chew. Do not drink alcohol if you are taking the extended-release capsule form (Kapspargo Sprinkle) — alcohol causes the medication to release too quickly.
• Immediate-release tablets (tartrate): Taken once daily or in divided doses, with food or right after a meal to help absorption. Doses are adjusted gradually at weekly intervals.
• Intravenous (tartrate injection): Given by a healthcare professional in a hospital or coronary care setting, then transitioned to oral metoprolol.

Your doctor will start you at a lower dose and adjust it based on your response. Never stop taking metoprolol on your own — always follow your prescriber's guidance.

Most side effects of metoprolol are mild and often improve as your body adjusts:

• Tiredness or fatigue
• Dizziness
• Depression
• Shortness of breath
• Slow heartbeat (bradycardia)
• Diarrhea
• Skin rash or itching
• Cold hands or feet, nausea, headache, or sleep disturbances (reported after approval)

Contact your doctor right away if you develop a very slow or irregular heartbeat, significant dizziness or fainting, sudden worsening of shortness of breath or chest pain, or signs of low blood sugar. These can signal a serious problem that needs prompt attention.

• Do not stop suddenly: Abruptly stopping metoprolol can cause worsening chest pain or trigger a heart attack — your doctor will taper your dose slowly over 1 to 2 weeks.
• Worsening heart failure: During dose increases, heart failure symptoms may temporarily worsen. Your doctor may adjust your diuretic and pause or lower the metoprolol dose before resuming.
• Breathing conditions: Metoprolol can cause bronchospasm (airway narrowing) and should generally be avoided in asthma or COPD. If it must be used, the lowest possible dose is recommended and rescue bronchodilators should be available.
• Surgery: Starting metoprolol at high doses right before non-cardiac surgery has been linked to bradycardia, low blood pressure, stroke, and death. However, do not stop it abruptly if you already take it regularly before surgery.
• Diabetes and hypoglycemia: Metoprolol can mask early warning signs of low blood sugar (like a racing heart). Monitor blood sugar closely and seek emergency help if you experience severe hypoglycemia.
• Thyroid disease: Stopping metoprolol suddenly in someone with an overactive thyroid (hyperthyroidism) can trigger a dangerous condition called thyroid storm.
• Severe allergic reactions: People with a history of serious allergic reactions may be more reactive to allergens while on metoprolol, and standard epinephrine doses to treat those reactions may be less effective.

Metoprolol can interact with several medications and substances that affect heart rate, blood pressure, or how the drug is processed in the body:

• CYP2D6 inhibitors (fluoxetine, paroxetine, quinidine, propafenone): Can significantly raise metoprolol blood levels, increasing the risk of slow heart rate and other side effects — monitor closely if these combinations cannot be avoided.
• Digoxin, diltiazem, verapamil, and clonidine: All slow the heart rate or AV conduction; combining with metoprolol raises the risk of dangerous bradycardia.
• Clonidine withdrawal: If you stop clonidine while on metoprolol, blood pressure can spike dangerously — metoprolol should be tapered first before stopping clonidine.
• Catecholamine-depleting drugs (reserpine, MAO inhibitors): Can cause an additive drop in blood pressure and heart rate.
• Alcohol (with extended-release capsule form): Causes rapid, uncontrolled release of the drug — avoid alcohol with Kapspargo Sprinkle.
• Epinephrine: Standard doses used to treat severe allergic reactions may be less effective in people on beta-blockers.

This is not a complete list of interactions. Always talk with your doctor or pharmacist before starting, stopping, or changing any medication.

• Tell your doctor if you have asthma, COPD, or any chronic breathing problem — metoprolol can narrow the airways.
• Metoprolol should generally not be used in people with severe bradycardia (very slow heart rate), second- or third-degree heart block, cardiogenic shock, or decompensated heart failure requiring IV support.
• If you have a pheochromocytoma (adrenal gland tumor), an alpha-blocker must be started before metoprolol is added.
• If you have diabetes, be aware metoprolol can hide early signs of low blood sugar — monitor carefully.
• If you have peripheral vascular disease (poor circulation in the limbs), metoprolol can worsen symptoms.
• Pregnancy: Metoprolol crosses the placenta. Newborns of mothers taking metoprolol may have low blood pressure, low blood sugar, slow heart rate, or breathing problems — your doctor will weigh the benefits and risks carefully.
• Breastfeeding: Metoprolol passes into breast milk in small amounts. Monitor your infant for slow heartbeat or signs of low blood sugar.
• Children: The extended-release succinate form has been studied in children aged 6 to 16 for high blood pressure; it has not been studied in children under 6.
• Older adults: Start at a lower dose — older adults are more likely to have liver, kidney, or heart conditions that affect how the drug behaves.
• If you have liver disease, your doctor should start you on a lower dose and increase slowly, since metoprolol is mainly broken down in the liver.
• Kidney disease generally does not require a dose adjustment — metoprolol clearance is not significantly affected by renal impairment.

Taking too much metoprolol can cause a dangerously slow heart rate, very low blood pressure, heart failure, heart block, loss of consciousness, bronchospasm, and nausea or vomiting. If you suspect an overdose, seek emergency medical care immediately. Standard epinephrine and adrenergic rescue drugs may be less effective in a metoprolol overdose, so intensive care is often needed — treatments may include medications to support the heart rate and blood pressure, bronchodilators for breathing problems, and in some cases glucagon.

Metoprolol slows the heart rate and reduces how hard the heart contracts, both at rest and during exercise, and it lowers blood pressure during exertion. It also dampens the rapid-heart-rate response triggered by certain medications and positional changes. In people with heart failure, metoprolol succinate has been shown to improve the heart's pumping function (left ventricular ejection fraction) and to slow the enlargement of the heart over time. At higher blood concentrations, its selective action on heart receptors decreases, and it begins to affect receptors in the lungs as well, which can cause airway narrowing in susceptible people.

When taken by mouth, metoprolol is partially broken down during its first pass through the liver, so blood levels from oral doses are roughly half those from an equivalent intravenous dose. It is primarily processed by the liver enzyme CYP2D6, and people who are slow metabolizers of this enzyme — or who take drugs that inhibit CYP2D6 — can have several-fold higher metoprolol blood levels. The drug has a half-life of approximately 3 to 7 hours, though the extended-release formulations are designed to release the drug slowly and maintain steadier blood levels over a full 24-hour period. Less than 5% of an oral dose leaves the body unchanged in the urine; the rest is excreted as inactive breakdown products by the kidneys. Liver disease can meaningfully raise blood levels; kidney disease does not significantly affect how the drug is handled.

Store at 25°C (77°F); excursions permitted to 15° to 30°C (59° to 86°F).