Beta Blocker

Labetalol

A beta blocker that also blocks α1 receptors, used for high blood pressure, including in pregnancy, and given IV for severe hypertension.

Drug card

Class: Beta blocker, and an alpha-1 blocker
How it works: Blocking beta receptors, so the heart beats slower and less forcefully
Used for: High blood pressure
High blood pressure in pregnancy
Severe hypertension, given intravenously
Known for: Dizziness on standing (postural hypotension)
Tingling of the scalp or skin, mostly at the start
Liver injury, including hepatic necrosis (rare)
Its name: -alol means a beta blocker (labetalol type)

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Mechanism of action

How does labetalol work?

Labetalol combines non-selective β blockade with selective α1 blockade; the β effect dominates, by about 3 to 1 taken by mouth and 7 to 1 intravenously. Because of the α1 block, blood pressure falls more when standing than lying down. Extensive first-pass metabolism leaves about 25% bioavailable, and its half-life is 6 to 8 hours.

Like other beta blockers: They block β-adrenergic receptors, so epinephrine and norepinephrine act less: in the heart (β1) rate and force of contraction fall and AV conduction slows, and the kidneys release less renin. Cardioselective ones (atenolol, bisoprolol, metoprolol) act mainly on β1; non-selective ones also block β2 in airways and vessels; carvedilol and labetalol block α1 as well.

Uses

What is labetalol used for?

High blood pressure
High blood pressure in pregnancy
Severe hypertension, given intravenously

Side effects

Side effects of labetalol

Dizziness on standing (postural hypotension)Known for
Tingling of the scalp or skin, mostly at the startKnown for
Liver injury, including hepatic necrosis (rare)Known forSerious
Dizziness
Nausea
Stuffy nose
Ejaculation failure and impotence
Slow heart rate (bradycardia)
Heart blockSerious
Narrowed airways (bronchospasm)Serious
Hidden warning signs of low blood sugarSerious
Floppy iris syndrome during cataract surgery

Known for marks what an exam expects you to know it for.

Watch for

Cautions and what sets it apart

Hepatic necrosis and deaths have occurred: liver tests are checked at the first sign of liver injury.
IV doses: standing up within 3 hours can bring on marked postural hypotension, so patients stay lying down.
Avoid in asthma, overt heart failure, heart block beyond first degree and severe bradycardia.
Babies of treated mothers can have low blood pressure, slow heart rate, low blood sugar and weak breathing.

Good to know: Its combined α1 and β blockade makes it a choice for high blood pressure in pregnancy and, given IV, for severe hypertension.

Remember it

A way to remember it

One heart, two lungs: β1 for the heart, β2 for the lungs.

β1 receptors dominate in the heart and β2 receptors in the airways. Cardioselective beta blockers act mainly on β1, so they narrow the airways less than non-selective ones such as propranolol, though all need care in asthma.

A mnemonic widely used in teaching

Its name

-alol means beta blocker (labetalol type)
USAN reads it as a combined alpha and beta blocker, which labetalol is. WHO defines it by chemical structure, as a sub-stem of -olol, and also lists sotalol.
Every drug name stem

Its class

Beta blockers

Other beta blockers with a card:

Easily mixed up with alpha-1 blockers and non-dihydropyridine calcium channel blockers.

All about beta blockers What “beta blocker” means, in the dictionary

Sources

Checked against

Written for biofideX in plain words, after checking these references:

For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.

Practice it

Blood pressure

Labetalol is one of 27 drugs practiced together here: their classes, how they work, what they treat and what they're known for.

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