Metoprolol

Metoprolol

[1 tablet 15 cents; 1 ampoule $6.80]

ADMINISTRATION ROUTES:

• PO, IV, NG

ALTERNATIVE NAMES:

• Lopressor, Betaloc, Metoprolol

ICU INDICATIONS:

1. hypertension
2. acute myocardial infarction
3. secondary prevention in patients with coronary artery disease
4. angina
5. rate control

PRESENTATION AND ADMINISTRATION:

• PO / NG
  Tablets:
  Lopressor 50mg tablets (pink), Lopressor 100mg tablets (light blue)
  Controlled Release tablets:
  Betaloc CR 23.75mg, 47.5mg, 95mg and 190mg tablets (white to off white)
  Oral Suspension:
  Metoprolol Suspension 1mg/ml
  Note: – non controlled release tablets may be crushed for NG administration.

• IV:
  Betaloc 5mg/5ml ampoules
  Inject undiluted solution at a rate of 1-2mg/min; usual dose 1-10mg/min
  Compatible with the following IV fluids:
  Normal saline, 5% or 10% glucose, Glucose and Sodium Chloride

DOSAGE:

• PO:
  25mg-100mg 8-12 hourly OR 23.75mg-190mg daily of controlled release tablets

DOSAGE IN RENAL FAILURE AND RENAL REPLACEMENT THERAPY:

• Dose in renal impairment [GFR (ml/min)]
  <10: start with small doses
  10-20: start with small doses
  >20-50: dose as in normal renal function
• Dose in renal replacement therapy
  CAPD: start with small doses
  HD: start with small doses
  CVVHDF: start with small doses

DOSAGE IN PAEDIATRICS:

• IV:
  0.1mg/kg over 5 minutes
• PO:
  1-2mg/kg 6-12 hourly

CLINICAL PHARMACOLOGY:

• Metoprolol is a beta-adrenergic receptor blocking agent. In vitro and in vivo animal studies have shown that it has a preferential effect on beta1 adrenoreceptors, chiefly located in cardiac muscle. This preferential effect is not absolute, however, and at higher doses, metoprolol also inhibits beta2 adrenoreceptors, chiefly located in the bronchial and vascular musculature.

CONTRAINDICATIONS:

1. sinus bradycardia
2. heart block greater than first degree
3. cardiogenic shock
4. overt cardiac failure
5. asthma

WARNINGS

• Cardiac Failure
  Sympathetic stimulation is necessary in supporting circulatory function in congestive heart failure, and beta blockade carries the potential hazard of further depressing myocardial contractility and precipitating more severe failure.
• Discontinuation of therapy
  Discontinuation of therapy in a patient with coronary artery disease may lead to rebound angina, arrhythmia or myocardial infarction.
• Diabetes and Hypoglycemia
  Beta blockers may mask tachycardia occurring with hypoglycaemia.
• Thyrotoxicosis
  Beta-adrenergic blockade may mask certain clinical signs (e.g., tachycardia) of hyperthyroidism. Abrupt withdrawal of beta blockade might precipitate a thyroid storm.

PRECAUTIONS

• General:
  Metoprolol may aggravate peripheral arterial circulatory disorders.
• Laboratory Tests:
  No tests in addition to routine ICU tests are required
• Drug/Laboratory Test Interactions:
  None known

IMPORTANT DRUG INTERACTIONS FOR THE ICU

• Beta blockers may exacerbate the rebound hypertension which can follow the withdrawal of clonidine

ADVERSE REACTIONS

• Body as a Whole:
  Tiredness, Fatigue
• Cardiovascular System:
  Bradycardia, Cold extremities, Hypotension, Leg pain
• Respiratory System:
  Wheeziness, Dyspnoea
• Digestive System:
  Diarrhoea, Nausea
• Nervous System:
  Dizziness, Vertigo, Light-headedness