Labetalol

Labetalol

[1 vial $17.72]

ADMINISTRATION ROUTES:

  • IV, PO

ALTERNATIVE NAMES:

  • Hybloc, Trandate

ICU INDICATIONS:

  1. hypertension

PRESENTATION AND ADMINISTRATION:

  • PO:
    Hybloc 50mg, 100mg, 200mg, 400mg
  • IV:
    100mg/20ml
    Bolus: 10-20mg over 2 minutes
    Infusion: 300mg in 60ml (undiluted) at a rate of 0-30 ml/hr (0-150mg/hr)
    Compatible with the following IV fluids:
    5% dextrose, glucose and sodium chloride, normal saline, Hartmanns

DOSAGE:

  • PO:
    50-100mg 12 hourly; may be increased to maximum of 600mg 6 hourly if required.

DOSAGE IN RENAL FAILURE AND RENAL REPLACEMENT THERAPY:

  • Dose as in normal renal function

DOSAGE IN PAEDIATRICS:

  • PO:
    1-2mg/kg 12 hourly; may increase to 10mg/kg 6 hourly
  • IV:
    0.25-0.5mg/kg over 2 minutes repeated every 10 minutes if required
    For infusion, 50mg/kg in 50ml of compatible IV fluid at 0-3ml/hr (0-3mg/kg/hr)

CLINICAL PHARMACOLOGY:

  • Labetalol hydrochloride is an adrenergic receptor blocking agent that has both selective alpha1-adrenergic and nonselective beta-adrenergic receptor blocking actions in a single substance. Labetalol is completely absorbed from the gastrointestinal tract with peak plasma levels occurring 1-2 hours after oral administration. The absolute bioavailability (fraction of drug reaching systemic circulation) of labetalol when compared to an IV infusion is 25%; this is due to extensive “first-pass” metabolism. Despite “first-pass” metabolism there is a linear relationship between oral doses of 100-3000 mg and peak plasma levels. The absolute bioavailability of labetalol is increased when administered with food.

CONTRAINDICATIONS:

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

WARNINGS

  • Hepatic Injury
    Severe hepatocellular injury, confirmed by rechallenge in at least one case, occurs rarely with labetalol therapy. The hepatic injury is usually reversible, but hepatic necrosis and death have been reported.
  • 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.
  • Rapid Decreases of Blood Pressure
    Caution must be observed when reducing severely elevated blood pressure. A number of adverse reactions, including cerebral infarction, optic nerve infarction, angina, and ischemic changes in the electrocardiogram have been reported with other agents when severely elevated blood pressure was reduced over time courses of several hours to as long as 1 or 2 days. The desired blood pressure lowering should therefore be achieved over as long a period of time as is compatible with the patient’s status.

PRECAUTIONS

  • General:
    Impaired Hepatic Function: Labetalol should be used with caution in patients with impaired hepatic function since metabolism of the drug may be diminished.
  • Laboratory Tests:
    No tests in addition to routine ICU tests are required
  • Drug/Laboratory Test Interactions:
    The presence of labetalol metabolites in the urine may result in falsely elevated levels of urinary catecholamines, metanephrine, normetanephrine, and vanillylmandelic acid when measured by fluorimetric or photometric methods. In screening patients suspected of having a pheochromocytoma and being treated with labetalol, a specific method, such as a high performance liquid chromatographic assay with solid phase extraction should be employed in determining levels of catecholamines.
    Labetalol has also been reported to produce a false-positive test for amphetamine when screening urine for the presence of drugs using the commercially available assay methods Toxi-Lab A (thin-layer chromatographic assay) and Emit-d.a.u. (radioenzymatic assay). When patients being treated with labetalol have a positive urine test for amphetamine using these techniques, confirmation should be made by using more specific methods, such as a gas chromatographic-mass spectrometer technique.

IMPORTANT DRUG INTERACTIONS FOR THE ICU

  • Beta blockers may exacerbate the rebound hypertension which can follow the withdrawal of clonidine. Drugs possessing beta-blocking properties can blunt the bronchodilator effect of beta-receptor agonist drugs in patients with bronchospasm; therefore, doses greater than the normal anti-asthmatic dose of beta-agonist bronchodilator drugs may be required.

ADVERSE REACTIONS

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

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