ADMINISTRATION ROUTES:
IV, PO
ALTERNATIVE NAMES:
Hybloc, Trandate
ICU INDICATIONS:
- Hypertension
PRESENTATION AND ADMINISTRATION:
PO:
Hybloc 50 mg, 100 mg, 200 mg, 400 mg
IV:
20 mL glass ampoules containing 100 mg (5 mg/mL)
Bolus via central venous line: Draw up 1 vial in a 20 mL syringe & administer undiluted through central line only
Infusion via central venous line: Draw up three 20 mL ampoules (each containing 100 mg) into a 60 mL syringe. Administer undiluted through central line only. Concentration is 5 mg/mL
Infusion via peripheral venous line: Peripheral venous administration requires dilution to 1 mg/mL. Add 200 mg (2 ampoules) to 160 mL. Concentration is 1 mg/mL
Compatible with the following IV fluids:
5% dextrose , normal saline, Hartmanns, glucose & sodium chloride
DOSAGE:
PO:
50-100 mg BD
Increase to max 600 mg QID if required
IV:
Bolus by central venous line:
10-50 mg (2-10 mLs) over 2 mins.
Repeat every 5 mins to max total dose 200 mg (40 mLs)
Infusion by central venous line:
Give at rate of 0-30 mL/hr (0-150 mg/hr)
Infusion by peripheral venous line:
Give at rate of 0-100 mL/hr (0-100 mg/hr)
Note: Administering dilute labetalol via a peripheral line at high infusion rates may cause fluid overload and contribute to hypertension. Consider administration via central line, switch to oral/nasogastric route, or use of an alternative agent
DOSAGE IN RENAL FAILURE AND RENAL REPLACEMENT THERAPY:
Dose as in normal renal function
DOSAGE IN PAEDIATRICS:
PO:
1-2 mg/kg bd
Increase to max 10 mg/kg QID if required
IV:
Bolus:
0.25-0.5 mg/kg over 2 mins
Repeat every 10 mins if required
Infusion:
Prepare 50 mg/kg in 50 mL of compatible IV fluid
Give at rate 0-3 mL/hr (0-3 mg/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% 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:
- Sinus bradycardia
- Heart block greater than first degree
- Cardiogenic shock
- Overt cardiac failure
- 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 Hypoglycaemia
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 ischaemic changes on ECG have been reported with other agents when severely elevated blood pressure was reduced over time courses of several hours to as long as 1-2 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.
Extravasation
Extravasation of undiluted labetalol (5 mg/mL) may cause ischaemia & necrosis due to the low pH of the solution. Only administer undiluted labetalol through a central venous line.
PRECAUTIONS:
General:
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 IN 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 pai
Respiratory System:
Wheeziness, Dyspnoea
Digestive System:
Diarrhoea, Nausea, Hepatitis
Nervous System:
Dizziness, Vertigo, Light-headedness