What are the FDA-approved uses of metoprolol. How does metoprolol work in the body. What are the administration methods for metoprolol. How does metoprolol compare to other beta-blockers. What are the potential side effects and contraindications of metoprolol.

Understanding Metoprolol: A Versatile Beta-Blocker

Metoprolol is a widely prescribed medication belonging to the class of drugs known as beta-blockers. It plays a crucial role in treating various cardiovascular conditions, offering benefits to patients with heart-related issues. This comprehensive guide delves into the intricacies of metoprolol, exploring its uses, mechanism of action, and administration methods.

FDA-Approved Uses of Metoprolol

The Food and Drug Administration (FDA) has approved metoprolol for several cardiovascular conditions. These include:

• Angina
• Heart failure
• Myocardial infarction (heart attack)
• Atrial fibrillation/flutter
• Hypertension (high blood pressure)

Additionally, metoprolol finds off-label use in treating supraventricular tachycardia and thyroid storm. The versatility of this medication makes it a valuable tool in managing various heart-related issues.

Metoprolol in Hypertension Management

Is metoprolol still considered a first-line treatment for hypertension? While metoprolol has been widely used for hypertension management, recent studies have questioned its role as initial therapy, particularly in patients without compelling indications. The debate surrounding the use of beta-blockers as first-line agents for hypertension continues, with some experts advocating for alternative treatments in certain patient populations.

Metoprolol in Post-Myocardial Infarction Care

How effective is metoprolol in reducing mortality after a heart attack? Several randomized trials conducted in the 1980s demonstrated a significant mortality benefit for beta-blockers, including metoprolol, in patients who had experienced an acute myocardial infarction. The Metoprolol Atherosclerosis Prevention in Hypertensives (MAPHY) trial specifically showed that metoprolol was superior to diuretics in reducing sudden cardiac death and myocardial infarction risk.

Mechanism of Action: How Metoprolol Works

Metoprolol exerts its therapeutic effects through a specific mechanism of action. Understanding this process is crucial for healthcare professionals and patients alike.

Beta-1 Receptor Blockade

How does metoprolol affect the heart? Metoprolol is a cardioselective beta-1-adrenergic receptor inhibitor. It competitively blocks beta-1 receptors with minimal or no effects on beta-2 receptors at oral doses of less than 100 mg in adults. This selective action results in:

• Decreased cardiac output
• Negative inotropic effect (reduced force of heart contractions)
• Negative chronotropic effect (reduced heart rate)

Unlike some other beta-blockers, metoprolol does not exhibit membrane-stabilizing or intrinsic sympathomimetic activity. This characteristic contributes to its specific cardiovascular effects.

Pharmacokinetics of Metoprolol

What happens to metoprolol in the body? Metoprolol is primarily lipophilic, allowing for efficient distribution throughout the body. When taken orally, it is almost completely absorbed from the gastrointestinal tract. However, significant hepatic first-pass elimination occurs, resulting in approximately 50% of the oral dose reaching systemic circulation.

The half-life of metoprolol is typically 3 to 4 hours for non-extended release tablets. Excretion primarily occurs via the kidneys, making dose adjustments necessary for patients with renal impairment.

Administration Methods and Formulations

Metoprolol is available in various formulations, each with specific administration requirements. Understanding these differences is essential for optimal therapeutic outcomes.

Oral Administration

How should metoprolol be taken orally? Metoprolol can be administered orally in two main formulations:

1. Immediate-release tablets (metoprolol tartrate):
   • Typically taken twice daily
   • Should be administered with or immediately following food intake
   • May be effective for hypertension when taken once daily, but lower doses may not provide 24-hour blood pressure control
2. Extended-release tablets (metoprolol succinate):
   • Can be taken once daily
   • Provides more consistent drug concentrations throughout the day
   • May be taken without regard to meals

Intravenous Administration

In certain clinical situations, metoprolol may be administered intravenously. This route is typically reserved for acute care settings and requires careful monitoring by healthcare professionals.

Comparing Metoprolol to Other Beta-Blockers

While metoprolol is a widely used beta-blocker, it’s essential to understand how it compares to other medications in its class.

Metoprolol vs. Carvedilol in Heart Failure

Is metoprolol or carvedilol more effective in treating heart failure? The Carvedilol or Metoprolol European Trial (COMET) compared these two beta-blockers head-to-head in patients with stable heart failure. The study found that carvedilol was associated with a statistically significant lower risk of all-cause death compared to metoprolol. However, recent trials have produced conflicting evidence on whether selective beta-1 blockers like metoprolol offer any advantage over non-selective beta-blockers like carvedilol in heart failure treatment.

Cardioselectivity of Metoprolol

How does the cardioselectivity of metoprolol impact its use? Metoprolol’s cardioselectivity means it primarily targets beta-1 receptors in the heart, with minimal effects on beta-2 receptors found in other tissues. This selectivity can be beneficial for patients with certain comorbidities, such as asthma or peripheral vascular disease, where non-selective beta-blockers might be contraindicated.

Potential Side Effects and Adverse Reactions

Like all medications, metoprolol can cause side effects. Being aware of these potential adverse reactions is crucial for both healthcare providers and patients.

Common Side Effects

What are the most frequently reported side effects of metoprolol? Common side effects may include:

• Fatigue
• Dizziness
• Bradycardia (slow heart rate)
• Hypotension (low blood pressure)
• Cold extremities
• Gastrointestinal disturbances

These side effects are generally mild and may improve as the body adjusts to the medication. However, if they persist or worsen, medical attention should be sought.

Serious Adverse Reactions

While rare, serious adverse reactions to metoprolol can occur. These may include:

• Severe bradycardia
• Heart block
• Worsening heart failure
• Bronchospasm (in patients with respiratory conditions)
• Depression
• Severe allergic reactions

Patients experiencing any of these serious side effects should seek immediate medical attention.

Contraindications and Precautions

Certain conditions and factors may preclude the use of metoprolol or require special consideration before initiating therapy.

Absolute Contraindications

When should metoprolol not be used under any circumstances? Absolute contraindications for metoprolol include:

• Severe bradycardia
• Heart block greater than first degree
• Cardiogenic shock
• Decompensated heart failure
• Severe peripheral arterial disease
• Known hypersensitivity to metoprolol or other beta-blockers

Relative Contraindications and Precautions

In what situations should metoprolol be used with caution? Relative contraindications and precautions include:

• Asthma or chronic obstructive pulmonary disease (COPD)
• Diabetes mellitus (may mask symptoms of hypoglycemia)
• Thyrotoxicosis (may mask symptoms)
• Peripheral vascular disease
• Pregnancy and breastfeeding (requires careful risk-benefit assessment)

In these cases, the potential benefits of metoprolol therapy must be carefully weighed against the risks, and close monitoring may be necessary.

Optimizing Metoprolol Therapy: Interprofessional Considerations

Effective use of metoprolol requires collaboration among healthcare professionals to ensure optimal patient outcomes.

Role of Pharmacists

How can pharmacists contribute to safe metoprolol use? Pharmacists play a crucial role in:

• Reviewing drug interactions and potential contraindications
• Educating patients on proper administration and potential side effects
• Monitoring for adherence and therapeutic efficacy
• Recommending dosage adjustments based on patient response and renal function

Nursing Considerations

What should nurses be aware of when caring for patients on metoprolol? Nurses should focus on:

• Monitoring vital signs, particularly heart rate and blood pressure
• Assessing for signs of worsening heart failure or other adverse effects
• Providing patient education on lifestyle modifications and medication adherence
• Communicating any concerns or changes in patient status to the healthcare team

Physician Oversight

How can physicians optimize metoprolol therapy? Physicians are responsible for:

• Selecting appropriate patients for metoprolol therapy
• Determining the optimal dosage and formulation
• Regularly assessing treatment efficacy and tolerability
• Adjusting therapy based on patient response and any emerging contraindications

By working together, these healthcare professionals can ensure that patients receive the maximum benefit from metoprolol therapy while minimizing potential risks.

Metoprolol – StatPearls – NCBI Bookshelf

Continuing Education Activity

Metoprolol is FDA-approved to treat angina, heart failure, myocardial infarction, atrial fibrillation/flutter, and hypertension. Off-label uses include supraventricular tachycardia and thyroid storm. Both oral and intravenous preparations are available. There are immediate and extended-release preparations available orally. There is controversy regarding the selection of beta-blockers in the management of the above conditions. There is also conflicting evidence regarding the optimal choice of a particular beta-blocker in treating each specific disease. This activity will highlight the mechanism of action, adverse event profile, pharmacology, monitoring, and relevant interactions of metoprolol, pertinent for members of the interprofessional team in the treatment of patients with conditions where it is of clinical value.

Objectives:

• Identify the mechanism of action of metoprolol.

• Describe the adverse effects of metoprolol.

• Summarize the contraindications of metoprolol.

• Employ interprofessional team strategies for enhancing care coordination and communication to advance the safe use of metoprolol and improve outcomes.

Access free multiple choice questions on this topic.

Indications

Metoprolol is FDA-approved to treat angina, heart failure, myocardial infarction, atrial fibrillation/flutter, and hypertension. Off-label uses include supraventricular tachycardia and thyroid storm. Both oral and intravenous preparations are available. There are immediate and extended-release preparations available orally. There is controversy regarding the selection of beta-blockers in the management of the above conditions. There is also conflicting evidence regarding the optimal selection of a particular beta-blocker in treating each specific disease.[1] The role of beta-blockers as initial therapy for hypertension, particularly in the absence of compelling indications, has been questioned. [2][3] 

Several randomized trials in the 1980s showed a mortality benefit for beta-blockers in acute myocardial infarction.[4][5][6] The Metoprolol Atherosclerosis Prevention in Hypertensives (MAPHY) trial specifically showed a benefit of metoprolol over diuretics regarding sudden cardiac death as well as myocardial infarction.[7] A large randomized trial of over 50,000 patients in the 1990s showed metoprolol to reduce mortality and re-infarction when used chronically after myocardial infarction.[8] Beta-blockers have demonstrated prognostic benefit and reduce mortality in the treatment of chronic heart failure. The carvedilol or metoprolol European trial (COMET) enrolled patients with stable heart failure and compared each drug head-to-head. Carvedilol was associated with a statistically significantly lower risk of all-cause death.[9] However, recent trials have had conflicting evidence on whether selective beta-1 blockers such as metoprolol have any benefit over other beta-blockers like carvedilol. [1]

Mechanism of Action

Metoprolol is a cardioselective beta-1-adrenergic receptor inhibitor that competitively blocks beta1-receptors with minimal or no effects on beta-2 receptors at oral doses of less than 100 mg in adults. It decreases cardiac output by negative inotropic and chronotropic effects. Metoprolol does not exhibit membrane stabilizing or intrinsic sympathomimetic activity. Administration of metoprolol to normal subjects results in a reduction in heart rate and cardiac output; this appears to be related to the dose and concentration of the drug. Metoprolol is mainly lipophilic, and distribution is typical of a basic lipophilic drug. Based on animal studies, it appears to be almost completely absorbed from the gastrointestinal (GI) tract when taken orally.

There is significant hepatic first-pass elimination, which results in around 50% of the oral dose reaching the systemic circulation. It is 11% bound to serum albumin. The half-life of metoprolol is about 3 to 4 hours in most patients for non-extended release tabs. Metoprolol excretion principally occurs via the kidneys.[10] Metoprolol succinate produces more level drug concentrations as compared to metoprolol tartrate, which has more peak-to-trough variation. However, despite these differences in pharmacokinetics, studies have concluded that both agents produce similar clinical effects, both acute and chronic.[11]

Administration

Metoprolol may administration can be either oral or intravenous. The immediate-release oral formulation is to be administered with or immediately following food intake. The administration of the short-acting formulation of metoprolol tartrate is usually twice daily. It may be effective for hypertension when taken once per day; however, lower doses may not control blood pressure for 24 hours. Patients may take the extended-release metoprolol succinate formulation without regard to meals.[12]

Adverse Effects

The primary adverse effects of metoprolol include heart failure exacerbation, fatigue, depression, bradycardia or heart block, hypotension, bronchospasm, cold extremities, dizziness, decreased libido, diarrhea, tinnitus, decreased exercise tolerance, glucose intolerance, and may mask hypoglycemia. Abrupt cessation of the drug may lead to a withdrawal syndrome that could cause angina or myocardial infarction. Tachycardia and hypertension are both common in withdrawal syndrome.[13]

Contraindications

Metoprolol is contraindicated in patients with sick sinus syndrome, second or third-degree heart block (in the absence of pacemaker),  decompensated heart failure, hypotension, and documented hypersensitivity to the drug or components. Also, caution is necessary for patients with a history of noncompliance as the abrupt cessation of the drug can lead to withdrawal syndromes, including angina and myocardial infarction. Patients who have ingested cocaine or methamphetamine have traditionally had a contraindication to the use of selective beta-blocker such as metoprolol. This observation has its basis on case reports, and there is no strong evidence that they cause any deleterious effects. Regardless, agents such as labetalol, which have alpha and beta activity, or calcium channel blockers should be used in these cases. Metoprolol is a pregnancy risk factor Category C drug.[14]

Monitoring

The onset of action for oral immediate-release tablets is within 1 hour, with a duration of effect variable depending on the dose given. The extended-release preparation has a similar onset of action and a duration of up to 24 hours. Metabolism of metoprolol is hepatic with excretion in the urine. If there is renal impairment, there is no dosage adjustment necessary. If there is a history of hepatic impairment, slowly increasing titrated doses to effect should be used. With the use of intravenous (IV) administration, cardiac monitor, including ECG heart rate and blood pressure, should be constant. Oral administration heart rate rhythm and blood pressure require monitoring.[14]

Toxicity

Treatment will vary based on the amount of metoprolol amount taken, comorbidities, age, and other co-investments. On arrival, assess ABCs and monitor appropriate blood work, including coingestants, ECG, large-bore IVs, and pregnancy status if female. Consult poison control/toxicology early in the course. Treatment choices include volume resuscitation, activated charcoal, whole bowel irrigation, nasogastric lavage, atropine, glucagon, calcium gluconate/calcium chloride, high-dose insulin, vasopressors, Intralipid, transcutaneous, or transvenous pacemaker. Cardiac status and a current fluid balance will guide volume resuscitation. Activated charcoal is typically given 1 g/kg and usually only has efficacy if dosed within 1 to 2 hours of ingestion.[15] If the patient has any altered mentation, caution is necessary to the possibility of aspiration. Whole bowel irrigation should be a consideration for extended-release preparations or large quantity ingestion.

Nasogastric lavage is usually ineffective, except for large quantity ingestions. The clinician may consider atropine use, although it is typically ineffective in moderate-to-severe overdoses. Calcium administration to increase intracellular calcium at a dose of 60 mg/kg over 5 to 10 minutes of calcium gluconate. Calcium chloride at a dose of 10 to 20 mL of a 10% solution is an option if central access is obtained. Glucagon dosing is 50 mcg/kg as a bolus with titration of drip. High-dose insulin at a dose of 1 unit per kilogram bolus followed by 1 unit per kilogram per hour drip.[16]

Administration with dextrose with a drip titrating to euglycemia as well as potassium repletion as needed. Vasopressors with epinephrine or norepinephrine titrated rate and blood pressure. Intralipid IV lipid emulsion therapy can serve as a lipid sink that extracts the drug from the myocyte. It may also provide free fatty acids as a substrate. It should be noted that the use of this medication will affect some laboratory monitoring.[17] Consider a transcutaneous or transvenous pacemaker. Extracorporeal membrane oxygenation (ECMO) should be considered for refractory cases.[18] If the clinician is concerned about intentional overdose, they should order a mandatory psychiatric evaluation. There may also be a need for the possibility of co-ingestants and treatment of those as well. For non-extended or non-sustained-release preparations, 4 to 6 hours of observation without any derangement of mental status or vital signs is sufficient. Any extended-release or sustained-release preparation requires 12 to 24 hours of telemetry observation, depending on the preparation. Extra caution should be considered in the pediatric population as very low amounts, including one pill or even one-half pill, which can cause cardiovascular collapse and death.[19]

Enhancing Healthcare Team Outcomes

Metoprolol is an effective beta-blocker for many cardiac disorders. However, prescribers of this drug should be aware that specific indications for this drug are still lacking. While research has shown the drug to lower mortality in CHF patients, the same applies to several other beta-blockers. To ensure the safe use of the drug, all members of the interprofessional healthcare team, including clinicians (MDs, DOs, NPs, and PAs), specialists, nurses, and pharmacists, should be very familiar with the indications, administration, and potential adverse effects and drug interactions of metoprolol, as well as all members of the beta-blocker drug classification, including which agents are specific vs. beta-1 specific. This will result in improved patient outcomes with fewer adverse events. [Level 5]

Metoprolol can be administered orally or IV and works quickly. 

Review Questions

• Access free multiple choice questions on this topic.

• Comment on this article.

References

1.

Fröhlich H, Zhao J, Täger T, Cebola R, Schellberg D, Katus HA, Grundtvig M, Hole T, Atar D, Agewall S, Frankenstein L. Carvedilol Compared With Metoprolol Succinate in the Treatment and Prognosis of Patients With Stable Chronic Heart Failure: Carvedilol or Metoprolol Evaluation Study. Circ Heart Fail. 2015 Sep;8(5):887-96. [PubMed: 26175538]

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Lindholm LH, Carlberg B, Samuelsson O. Should beta blockers remain first choice in the treatment of primary hypertension? A meta-analysis. 2005 Oct 29-Nov 4Lancet. 366(9496):1545-53. [PubMed: 16257341]

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Khan N, McAlister FA. Re-examining the efficacy of beta-blockers for the treatment of hypertension: a meta-analysis. CMAJ. 2006 Jun 06;174(12):1737-42. [PMC free article: PMC1471831] [PubMed: 16754904]

4.

Hjalmarson A, Herlitz J, Holmberg S, Rydén L, Swedberg K, Vedin A, Waagstein F, Waldenström A, Waldenström J, Wedel H, Wilhelmsen L, Wilhelmsson C. The Göteborg metoprolol trial. Effects on mortality and morbidity in acute myocardial infarction. Circulation. 1983 Jun;67(6 Pt 2):I26-32. [PubMed: 6342837]

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Intravenous beta-blockade during acute myocardial infarction. Lancet. 1986 Jul 12;2(8498):79-80. [PubMed: 2873383]

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Sleight P. Use of beta adrenoceptor blockade during and after acute myocardial infarction. Annu Rev Med. 1986;37:415-25. [PubMed: 2871805]

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Wikstrand J, Warnold I, Tuomilehto J, Olsson G, Barber HJ, Eliasson K, Elmfeldt D, Jastrup B, Karatzas NB, Leer J. Metoprolol versus thiazide diuretics in hypertension. Morbidity results from the MAPHY Study. Hypertension. 1991 Apr;17(4):579-88. [PubMed: 2013485]

8.

Freemantle N, Cleland J, Young P, Mason J, Harrison J. beta Blockade after myocardial infarction: systematic review and meta regression analysis. BMJ. 1999 Jun 26;318(7200):1730-7. [PMC free article: PMC31101] [PubMed: 10381708]

9.

Remme WJ, Cleland JG, Erhardt L, Spark P, Torp-Pedersen C, Metra M, Komajda M, Moullet C, Lukas MA, Poole-Wilson P, Di Lenarda A, Swedberg K. Effect of carvedilol and metoprolol on the mode of death in patients with heart failure. Eur J Heart Fail. 2007 Nov;9(11):1128-35. [PubMed: 17716943]

10.

Brogden RN, Heel RC, Speight TM, Avery GS. Metoprolol: a review of its pharmacological properties and therapeutic efficacy in hypertension and angina pectoris. Drugs. 1977 Nov;14(5):321-48. [PubMed: 201441]

11.

Kukin ML, Mannino MM, Freudenberger RS, Kalman J, Buchholz-Varley C, Ocampo O. Hemodynamic comparison of twice daily metoprolol tartrate with once daily metoprolol succinate in congestive heart failure. J Am Coll Cardiol. 2000 Jan;35(1):45-50. [PubMed: 10636257]

12.

Wikstrand J, Hjalmarson A, Waagstein F, Fagerberg B, Goldstein S, Kjekshus J, Wedel H., MERIT-HF Study Group. Dose of metoprolol CR/XL and clinical outcomes in patients with heart failure: analysis of the experience in metoprolol CR/XL randomized intervention trial in chronic heart failure (MERIT-HF). J Am Coll Cardiol. 2002 Aug 07;40(3):491-8. [PubMed: 12142116]

13.

Helfand M, Peterson K, Christensen V, Dana T, Thakurta S. Drug Class Review: Beta Adrenergic Blockers: Final Report Update 4 [Internet]. Oregon Health & Science University; Portland (OR): Jul, 2009. [PubMed: 21089245]

14.

Ripley TL, Saseen JJ. β-blockers: a review of their pharmacological and physiological diversity in hypertension. Ann Pharmacother. 2014 Jun;48(6):723-33. [PubMed: 24687542]

15.

Graudins A, Lee HM, Druda D. Calcium channel antagonist and beta-blocker overdose: antidotes and adjunct therapies. Br J Clin Pharmacol. 2016 Mar;81(3):453-61. [PMC free article: PMC4767195] [PubMed: 26344579]

16.

Stellpflug SJ, Harris CR, Engebretsen KM, Cole JB, Holger JS. Intentional overdose with cardiac arrest treated with intravenous fat emulsion and high-dose insulin. Clin Toxicol (Phila). 2010 Mar;48(3):227-9. [PubMed: 20141425]

17.

Walter E, McKinlay J, Corbett J, Kirk-Bayley J. Review of management in cardiotoxic overdose and efficacy of delayed intralipid use. J Intensive Care Soc. 2018 Feb;19(1):50-55. [PMC free article: PMC5810865] [PubMed: 29456602]

18.

Chenoweth JA, Colby DK, Sutter ME, Radke JB, Ford JB, Nilas Young J, Richards JR. Massive diltiazem and metoprolol overdose rescued with extracorporeal life support. Am J Emerg Med. 2017 Oct;35(10):1581.e3-1581.e5. [PubMed: 28705745]

19.

Euwema MS, Swanson TJ. StatPearls [Internet]. StatPearls Publishing; Treasure Island (FL): Aug 1, 2022. Deadly Single Dose Agents. [PubMed: 28722879]

Disclosure: Jason Morris declares no relevant financial relationships with ineligible companies.

Disclosure: Alexis Dunham declares no relevant financial relationships with ineligible companies.

What are the side effects of Metoprolol (Lopressor / Toprol XL)?

Written by: Nicole Mitton

Reviewed by: Dr Tamlyn Maree

• Metoprolol (Lopressor / Toprol XL)
• Warnings when taking Metoprolol (Lopressor / Toprol XL)?
• What are the side effects of Metoprolol (Lopressor / Toprol XL)?
• Can Metoprolol (Lopressor / Toprol XL) interfere with other medications?
• Metoprolol (Lopressor / Toprol XL) outlook

There are a number of possible metoprolol side effects, it is best to speak to your doctor about these and consult with him/her should any of these persist and become bothersome. The side effects listed below pertain to the orally administered form of this medication.

• NOTE: If you experience symptoms of an allergic reaction which often involve a combination of itching, the development of a rash or hives, difficulty breathing and noticeable swelling of the face, lips, throat and / or tongue visit your doctor or an emergency room immediately.

Common metoprolol side effects

Some of the more common side effects that may be experienced when taking metoprolol (sold as Lopressor, Toprol XL, Betaloc, Lopresor) include:

• Bradycardia (abnormally slow heart beat): This is defined as a resting heart rate of 60 beats per minute or less. Metoprolol slows down nerve impulses travelling from the brain to the heart, which can, in turn, slow your heart rate. A severely lowered pulse can compromise oxygen flow to the brain and body. Symptoms of this condition include:
  • Fatigue
  • Confusion
  • Dizziness
  • Shortness of breath
  • Fainting
  • Chest pains
  • Cold hands and feet

  
  If you experience severe symptoms, visit your doctor or nearest emergency room.

• Cold hands and feet: The slowing of the heart rate and lowering of the blood pressure caused by this medication can result in decreased circulation and less blood being pumped to the hands and feet. This results in a loss of warmth, making them feel cold and, on occasion, painful.
• Diarrhoea: Metoprolol can block the nerve signals sent from the brain to the gut which can affect the digestive system, either speeding it up or slowing it down. If it moves faster it can result in diarrhoea, and if it moves slower it results in constipation.
• Dizziness: Due to its blood pressure lowering effects, metoprolol may cause mild dizziness, particularly when moving quickly from a lying or seated position to a standing one (this has been reported in 2 to 10% of users). This feeling will often disappear when the body has adjusted to the drug. However, severe drops in blood pressure may result in severe dizziness and fainting, which is considered a serious side effect. It is best to consult with a doctor should you experience either of these.
• Fatigue, drowsiness and weakness: Metoprolol will slow your heart rate down by blocking the hormone adrenaline. This results in blood being transported to the brain and body at a slower pace, making some feel tired (reported in 1 to 10% of cases), drowsy and weak. This symptom may fade after a few days when first taking the drug as the body adapts to its effects. If fatigue persists or worsens, speak to your doctor.
• Gastrointestinal issues: In addition to diarrhoea, metoprolol may cause other gastrointestinal issues such as constipation, abdominal pain, heartburn, bloating, gas, flatulence, nausea and vomiting.
• Headache
• Heart palpitations: With beta blocker use the atrium (the upper chamber in which blood enters the heart) does not fill or contract as hard and effectively. The atrium then becomes stretched and stiff. This causes poor conduction of the electric signal telling the heart to contract and ultimately leads to irregular heartbeats and atrial fibrillation (a condition wherein the upper and lower chambers of the heart to beat irregularly out of sync). If you experience palpitations, shortness of breath and fatigue after taking metoprolol, speak to your doctor as he/she may wish to change your medication.
• Hypotension (low blood pressure): Metoprolol is prescribed to lower blood pressure. If the dosage is too high, this may result in a severe drop in blood pressure. This can also be a result of heart receptors being overly sensitive to the drug. Symptoms of hypotension may include light-headedness, severe dizziness or fainting.
• Shortness of breath: This symptom may be experienced, particularly when engaging in physical activity, due to the fact that metoprolol hinders the effect of adrenaline (epinephrine) and noradrenaline (norepinephrine) on the lungs. These hormones relax the small airways (bronchioles) of the lungs, making breathing easier, when they are inhibited, shortness of breath may occur. Metoprolol also affects cardiac output (reducing the volume of blood that is pumped by the heart) which can decrease the amount of oxygen in the body, leaving you short of breath. If you have a predisposition to respiratory issues or experience this side effect, discuss this with your doctor during your initial consultation or as soon as possible after being prescribed and taking this medication. Beta blockers such as Metoprolol are rarely prescribed to patients with asthma as this medication can exacerbate this condition.

Other side effects of metoprolol

In addition to the above, other side effects may include:

• Chest pain / discomfort: Metoprolol, despite being used to treat chest pain (angina), may actually cause or worsen it in some people. This is due to the fact that it slows the heart rate, which in severe cases can lead to pain. Never ignore chest pain, always get checked out by your doctor to be safe.
• Depression: While depression is often listed as a metoprolol side effect as it has been reported by between 2 and 5% of users in clinical studies¹, comprehensive studies^2,3 which have examined this specific side effect have not conclusively proven or disproven metoprolol’s link to drug-induced depression as yet. It is believed that those suffering from the chronic health problems for which metoprolol is often prescribed may be more susceptible to suffering depression as well. If you do find yourself feeling depressed after using this medication, always consult your doctor.
• Difficulty breathing and coughing: As mentioned above, metoprolol can cause shortness of breath due to the fact that it blocks the action of adrenaline on the lungs and affects the heart’s ability to pump oxygen through the blood, making it more difficult to breathe. In some instances, this inhibitory action may lead to asthma-like symptoms such as trouble breathing. Coughing and wheezing may occur. If you experience these side effects, consult your doctor.
• Fluid retention: This may lead to swelling of the face, limbs, hands and feet.
• Heart conduction disturbances: This may result from a lowered heart rate due to metoprolol use, causing what is known as a first degree atrioventricular block. In this condition, electrical impulses in the heart are slowed, generally symptoms or issues are rare.
• Increase in perspiration / sweating (diaphoresis): Metoprolol can cause heat sensitivity and excessive perspiration in some.
• Musculoskeletal pain and arthralgia (joint pain)
• Skin Issues: Metoprolol may induce the following skin related issues as side effects:
• Pruritis: Metoprolol can cause a severe itching of the skin that may be accompanied by a burning sensation.
• Rash: Skin rashes can start to develop as a result of metoprolol use. Hives and itching can also be experienced, this is considered seriousand it is important to seek professional advice from your doctor should you experience this symptom.
• Tingling in the skin / Pins and needles
• Sleep disturbances: Metoprolol may cause issues with sleep in some, these include:
• Issues with falling and staying asleep (insomnia)
• Nightmares
• Weight gain: Metoprolol (Lopressor, Toprol XL) may cause slight weight gain as a side effect. Generally, a gain of 1.2kg (2.6lb) is average. If you are taking Metoprolol to prevent heart failure and suddenly gain more than this in a day and more than 2.3kg (5.1lb) in a week, make an appointment to see your doctor immediately as this may indicate a build-up of fluid in your body, rather than actual weight gain which may be a result of your condition worsening.
• Worsening of heart failure symptoms: This may occur initially but is usually only temporary and generally resolves. You should work closely with your doctor if your symptoms worsen after taking metoprolol.

Rare metoprolol side effects

Rare metoprolol side effects affect 1 in 1000 people. They are considered to be^4,5:

• Anxiety and nervousness
• Changes in liver test results
• Dry mouth (Xerostomia)
• Hair loss (alopecia): Hair loss may occur, this is, however, reversible once the medication is stopped.
• Irregular heart beat (arrhythmia)
• Runny nose
• Sexual dysfunction: In men metoprolol can disrupt the section of the brain that signals an erection during sexual arousal, causing impotence. The same mechanism can also make orgasm difficult for both sexes when taking this medication.
• Peyronie’s syndrome (a condition which causes the penis to bend on erection) may also occur in rare instances.

• Visual disturbances: Visual side effects reported when taking Metoprolol include:
• Blurred vision which may cause difficulty in focussing on objects both near and far. This is due to the fact that beta blockers like metoprolol can lower intraocular pressure (IOP) by decreasing fluid production in the eye⁶. When IOP is very low, this may lead to blurred vision.
• Double vision
• Dry eyes⁷ (as a result of metoprolol reducing fluid production in the eye)
• Conjunctivitis

• Unstable diabetes

Very rare side effects of metoprolol

Affecting 1 in 10,000 people, very rare metoprolol (lopressor / Toprol XL) side effects include:

• Arthritis
• Changes in blood cells
• Changes in blood triglycerides and a decrease in High Density Lipoprotein (i. e. the ‘good’ type of cholesterol).
• Changes in taste: Things that once tasted good may not taste the same, this can affect appetite.
• Cognitive issues:
• Confusion
• Forgetfulness
• Hallucinations
• Temporary memory loss (amnesia)
• Changes in personality (mood)

• Hearing issues:
• Difficulty hearing
• Ringing in the ears (tinnitus)

• Light sensitivity (photosensitivity)
• Liver inflammation (hepatitis)
• Jaundice (yellowing of the skin, mucous membranes and whites of the eyes due to high levels of bilirubin in the body)
• Psoriasis (new cases or exacerbation of existing ones)
• Tissue death (necrosis) in those suffering from severe circulation disorders.

References

<sup>1. Harvard Health Publishing. Harvard Medical School. October 2015. Is your medication making you depressed? Available: https://www.health.harvard.edu/drugs-and-medications/is-your-medication-making-you-depressed [Accessed 18.07.2018]
2. US National Library of Medicine. December 2008. General Medical Drugs Associated with Depression. Available: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2729620/ [Accessed 18.07.2018]
3. US National Library of Medicine. January 2017. Impact of metoprolol treatment on mental status of chronic heart failure patients with neuropsychiatric disorders. Available: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5279819/ [Accessed 18.07.2018]
4. The electronic Medicines Compendium (eMC). Metoprolol tartrate film-coated tablets. Available: https://www.medicines.org.uk/emc/files/pil.5200.pdf [Accessed 18.07.2018]
5. US Food and Drug Administration. LOPRESSOR (metoprolol tartrate) tablet. Available: https://www.accessdata.fda.gov/drugsatfda_docs/label/2008/017963s062,018704s021lbl. pdf [Accessed 18.07.2018]
6. The Optometric Extension Program Foundation. Ocular & visual side effects of systemic drugs. Available: https://www.oepf.org/sites/default/files/journals/jbo-volume-11-issue-6/11-6%20Valeriewren.pdf [Accessed 18.07.2018]
7. Research Gate. August 2012. The Role of Medications in Causing Dry Eye. Available: https://www.researchgate.net/publication/232227209_The_Role_of_Medications_in_Causing_Dry_Eye [Accessed 18.07.2018]</sup>

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Selective beta-1 adrenergic blockers in the treatment of high blood pressure

Relevance

Selective beta-1 blockers are a subclass of beta-blockers commonly used to treat high blood pressure (BP). Drugs in this class include atenolol (Tenormin), metoprolol (Lopressor), nebivolol (Bystolic), and bisoprolol (Zebeta, Monocor). We have developed a comprehensive methodology to study the effectiveness of lowering blood pressure with various doses and drugs of this class of drugs.

Description of included studies

We identified and included in the review 56 clinical trials investigating the blood pressure lowering effect of eight beta-1 blockers in 7812 participants with high blood pressure. These participants were randomized to either a fixed dose beta-1 blocker or placebo for 3-12 weeks.

Main results

On average, beta-1 blockers lower blood pressure by 10 millimeters systolic and 8 millimeters diastolic pressure in people with mild to moderate high blood pressure. In general, higher doses of beta-1 blockers did not show a greater reduction in blood pressure than lower doses. The maximum reduction in blood pressure was recorded at a dose twice the recommended starting dose.

Higher doses of beta-1 blockers reduced heart rate more than lower doses, so they are more likely to cause the overall side effect of slowing heart rate. Beta-1 selective blockers reduce systolic and diastolic blood pressure to the same extent as other subclasses of beta-blockers, and thus have little or no effect on pulse pressure. This distinguishes them from other classes of antihypertensive agents such as thiazide diuretics, angiotensin-converting enzyme inhibitors, and angiotensin receptor blockers.

Quality of evidence

The quality of the evidence was considered to be low due to various types of bias that may exaggerate the effect. The low quality of the evidence means that further studies are likely to have a major impact on our confidence in the effect estimate and are likely to change this estimate.