Betaloc – metoprolol tartrate

metoprolol tartrate – cardioselective beta-blocker

• 50 mg and 100 mg tablets (95% absorbed)
• 1 mg / mL Injection solution
  • up to 5 mg IV at a rate of 1-2 mg per minute, q 5-minutely (max. 10-15 mg)
    • BP and ECG should be monitored during treatment
• Pregnancy category: C
• Small amounts in breast milk

Contraindications

• Bronchospasm (and atopy suggesting predisposition to bronchospasm)
• Right ventricular failure
• Sinus bradycardia < 45-50 bpm
• Second / third degree A-V block
• Shock and decompensated CCF
• Sick-sinus syndrome (except in case of PPM)
• Severe PAI
• Hypotension < 100 mmHg
• Untreated pheochromocytoma

Metoprolol tartrate structurally belongs to the class of cardioselective beta-blockers. Its cardiac β₁ receptor action occurs at lower doses than that of its bronchiolar and peripheral vasculature effect. Metoprolol shows no partial agonist activity (intrinsic sympathomimetic activity) at doses required to produce beta-blockade.

• Reduces standing and supine BP and the blood pressure rise in response to exercise and (catecholaminergic) stress
• Reduces frequency and severity of angina pectoris and increases exercise tolerance
• Reduces mortality in AMI
  • lower incidence of VF and limitation of infarct size
  • reduce incidence of recurrent AMI
• Regulates heart rate in SVT, AF, and those with extra-systoles

Indications

• Hypertension: 50 mg daily for 1 week increasing up to 100 mg twice daily
• Prophylaxis of angina pectoris: 50-100 mg bd-tid
• acute myocardial infarction: 50 mg twice daily for 48 hours, then 100 mg twice daily
• (prophylaxis of migraine: 50 mg bd)
• Supraventricular tachycardia (intravenous use)

Duration of beta-blockade is dose dependent: for instance, effect of 20 mg intravenously is halved after about 6 hours. There is no active metabolite, and more than 90% of metoprolol tartrate is excreted in urine within 72 hours, giving an elimination half-life between 3 and 5 hours.

Precautions

• Depressed myocardial contractility
• Prinzmetal angina
• First-degree A-V block
• Diabetes mellitus especially on OHAs or insulin – masks symptoms of hypoglycaemia
• Allergic conditions such as allergic rhinitis
• Liver disease
• Abrupt withdrawal – reduce the dose gradually over 1-2 weeks

Interactions

• Non-dihydropyridine calcium antagonists – verapamil, diltiazem
• Antiarrhythmic agents
• Antihypertensive drugs
• Sympathetic ganglion blocking agents and monoamine oxidase inhibitors
• Liver enzyme enhancers (e.g. rifampicin) and inhibitors (e.g. cimetidine, hydralazine)
• Oral Hypoglycaemic agents and insulin – risk of unrecognised hypoglycaemia

Particularly at the start of treatment, beta blockers may give rise to exertional tiredness as well as sleep disturbance and nightmares. More common adverse effects include:

• Bradycardia
• Postural hypotension
• Raynaud’s phenomenon (cold hands and feet)
• Dizziness, headache
• Bronchospasm – usually reversible with bronchodilators

Over-dosage should be treated with atropine, sympathomimetic drugs, or pacing.

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Reference: Betaloc® (metoprolol tartrate) Product Information. Nov 3, 2017. Astra Zeneca.