Labetalol (Labetalol Hydrochloride) - Drug Interactions, Contraindications, Overdosage

DRUG INTERACTIONS

Risk of Anaphylactic Reaction

While taking beta-blockers, patients with a history of severe anaphylactic reaction to a variety of allergens may be more reactive to repeated challenge, either accidental, diagnostic, or therapeutic. Such patients may be unresponsive to the usual doses of epinephrine used to treat allergic reaction.

OVERDOSAGE

Overdosage with labetalol causes excessive hypotension that is posture sensitive, and sometimes, excessive bradycardia. Patients should be placed supine and their legs raised if necessary to improve the blood supply to the brain. If overdosage with labetalol follows oral ingestion, gastric lavage or pharmacologically induced emesis (using syrup of ipecac) may be useful for removal of the drug shortly after ingestion. The following additional measures should be employed if necessary: Excessive Bradycardia - administer atropine or epinephrine. Cardiac Failure - administer a digitalis glycoside and a diuretic. Dopamine or dobutamine may also be useful. Hypotension - administer vasopressors, e.g., norepinephrine. There is pharmacological evidence that norepinephrine may be the drug of choice. Bronchospasm - administer epinephrine and/or an aerosolized beta₂-agonist. Seizures - administer diazepam.

In severe beta-blocker overdose resulting in hypotension and/or bradycardia, glucagon has been shown to be effective when administered in large doses (5 to 10 mg rapidly over 30 seconds, followed by continuous infusion of 5mg/hr that can be reduced as the patient improves).

Neither hemodialysis nor peritoneal dialysis removes a significant amount of labetalol from the general circulation (<1%).

The oral LD₅₀ value of labetalol HCl in the mouse is approximately 600 mg/kg and in the rat is greater than 2g/kg. The intravenous LD₅₀ in these species is 50 to 60 mg/kg.

CONTRAINDICATIONS

Labetalol tablets are contraindicated in bronchial asthma, overt cardiac failure, greater than first degree heart block, cardiogenic shock, severe bradycardia, other conditions associated with severe and prolonged hypotension, and in patients with a history of hypersensitivity to any component of the product (see WARNINGS).

Beta-blockers, even those with apparent cardioselectivity, should not be used in patients with a history of obstructive airway disease, including asthma.