Labetalol is a drug that is used for treating high blood pressure. And is related to carvedilol (Coreg). Nerves from the adrenergic nervous system travel from the spinal cord to arteries where they release norepinephrine. Norepinephrine attaches to adrenergic receptors on arteries and causes the arteries to contract, narrowing the arteries, and increasing blood pressure. Labetalol blocks receptors of the adrenergic nervous system. When labetalol attaches to and blocks the receptors, arteries expand, resulting in a fall in blood pressure. The FDA approved labetalol in August 1984.

None. Normodyne and Trandate are discontinued.

Yes

Yes

The most common side effects of labetalol are:

• fatigue,
• dizziness,
• nausea,
• headache,
• diarrhea,
• edema (fluid accumulation), and
• shortness of breath.

Postural hypotension (a rapid decrease in blood pressure when going from the lying or seated position to the standing position that may cause light-headedness or fainting) occurs rarely. Patients should be observed for this possible side effect within two to four hours of the first labetalol dose and after any changes in dose.

Other important side effects include:

• sexual dysfunction,
• abnormal heart rhythm,
• slow heart rate,
• liver failure, and
• allergic reactions.

The recommended starting oral dose of labetalol is 100 mg twice daily and the dose can be increased by 100 mg twice daily every 2-3 days based on the response of the blood pressure. Usual maintenance doses are 200-400 mg twice daily. Patients with severely high blood pressure may require 1.2 to 2.4 g daily.

Side effects may be less if labetalol is given in three daily doses rather than two. Stopping or changing the dose of the drug should be directed by a physician because serious side effects may occur. The initial intravenous dose of labetalol is 20 mg injected over 2 minutes. Additional injections of 40 or 80 mg may be administered every 10 minutes as needed up to a total dose of 300 mg. Labetalol also may be administered by intravenous infusion at 1-2 mg/minute.

Labetalol can mask early warning symptoms of hypoglycemia (low blood sugar) such as tremors and increased heart rate which are the result of activation of the adrenergic nervous system. Therefore, people with diabetes taking medications that lower blood sugar such as insulin or oral antidiabetic medications may need to increase the frequency with which they monitor their blood sugar in order to prevent hypoglycemia.

Combining labetalol with tricyclic antidepressants such as amitriptyline (Elavil, Endep), imipramine (Tofranil), or nortriptyline (Pamelor) may lead to an increase in tremor which is a side effect of tricyclic antidepressants.

If combined with adrenergic stimulating drugs used for treating asthma, for example, albuterol (Proventil, Ventolin) or pirbuterol (Maxair), the adrenergic blocking effects of labetalol may counteract the effects of the stimulating drugs and reduce their effectiveness for treating asthmatic attacks. More of the adrenergic drug may be needed.

Glutethimide (Doriden) may decrease the effectiveness of labetalol by increasing its elimination. When both drugs are used together, more labetalol or less glutethimide may be needed.

Cimetidine (Tagamet) may increase the effectiveness of labetalol by blocking its elimination and increasing its levels in the blood. Therefore, less labetalol may be needed when cimetidine and labetalol are used together.

Halothane anesthesia may contribute to the blood pressure lowering effects of labetalol.

There are no adequate studies of labetalol during pregnancy.

Labetalol is excreted in human breast milk. Therefore, it should be used cautiously in nursing mothers because of the risk that the infant may develop a slow heart rate.

How should I keep labetalol stored?

Tablets should be stored between 20 C - 30 C (36 F - 86 F).