Metoprolol

Metoprolol is a selective beta₁ receptor blocker used in treatment of several diseases of the cardiovascular system, especially hypertension. It is marketed under the brand name Lopressor or Lopresor, respectively, by Novartis, and Toprol-XL (in the USA); Seleken or Selokeen (elsewhere); as Minax by Alphapharm (in Australia), Metrol by Arrow Pharmaceuticals (in Australia), as Betaloc by AstraZeneca, as Neobloc by Unipharm (in Israel) and as Corvitol by Berlin-Chemie AG. A number of generic products is available, too. The active substance metoprolol is employed either as metoprolol succinate or metoprolol tartrate (whereas 100 mg metoprolol tartrate corresponds to 95 mg metoprolol succinate), as conventional release- or prolonged-release formulation.

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Physical properties

Metoprolol is very low melting. Its melting point is around 45 degrees Celsius (as determined by Differential scanning calorimetry). For this reason metoprolol is always manufactured in salt form, as drugs with melting points below 100 degrees Celsius are difficult to work with in a manufacturing environment. The free base exists as a waxy white solid, where the tartrate salt is finer crystalline material.

Pharmacology

• Cardioselective
• Moderately Lipophilic
• Without intrinsic sympathomimetic activity (ISA)
• With weak membrane stabilizing activity
• Short half-life must be taken at least twice daily or as an Slow-release preparation.

Indications

• Essential hypertension
• Coronary heart disease (prevention of angina attacks)
• Secondary prevention after a myocardial infarction
• Treatment of heart failure.^[1]
• Migraine prophylaxis
• Adjunct in treatment of hyperthyroidism

Side effects

Side effects are usually mild. Transient effects include dizziness, lightheadedness, drowsiness, tiredness, diarrhea, unusual dreams, ataxia, trouble sleeping, and vision problems. It may also reduce blood flow to the hands and feet, causing them to feel numb and cold; smoking may worsen this effect.^[2]

Serious side effects that are not to be tolerated for any length of time include symptoms of a very slow heartbeat (e.g. persistent dizziness, fainting, unusual fatigue), bluish discoloration of the fingers and toes, numbness/tingling/swelling of the hands or feet, sexual dysfunction, erectile dysfunction (impotence), hair loss, mental/mood changes, trouble breathing, cough, unexplained or sudden weight gain, and increased thirst. Other highly unlikely symptoms include easy bruising or bleeding, persistent sore throat or fever, yellowing skin or eyes, stomach pain, dark urine, and persistent nausea. Symptoms of an allergic reaction include: rash, itching, swelling, severe dizziness.^[2]

References

1. ^ (June 12 1999) "Effect of metoprolol CR/XL in chronic heart failure: Metoprolol CR/XL Randomised Intervention Trial in Congestive Heart Failure (MERIT-HF)". Lancet 353 (9169): 2001-7. PMID 10376614.
2. ^ ^{a b} Canadian Online Pharmacy website: Metoprolol