Detailed Drug Information:

DRUG CLASS AND MECHANISM: Labetalol is used for treating high blood pressure. It is related to carvedilol (Coreg). Labetalol blocks receptors of the adrenergic nervous system, the system of nerves in which epinephrine (adrenalin) is active. Nerves from the adrenergic system within the arteries release an adrenergic chemical (norepinephrine) that attaches to the receptors on the muscles of the arteries and causes the muscles to contract, narrowing the arteries, and increasing blood pressure. When labetalol attaches to and blocks the receptors, the arterial muscles relax, and the arteries expand, resulting in a fall in blood pressure. The FDA first approved labetalol in 1997.

PREPARATION: Tablets of 100 mg, 200 mg (generic, Trandate, Normodyne); tablets of 300 mg (generic,Normodyne).

STORAGE: Tablets should be stored between 2-30°C(36-86°F).

PRESCRIBED FOR: Labetalol is used alone or with a diuretic ("water-pill") from the thiazide class, e.g., hydrochlorothiazide (Hydrodiuril) or the loop class, e.g., furosemide (Lasix) to control high blood pressure.

DOSING: Labetalol may be given two or three times daily. The starting dose is 100mg twice daily with a maximum of 400mg twice daily. Patients with severe high blood pressure may require larger doses than 400mg twice 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.

DRUG INTERACTIONS: Labetalol can mask early warning symptoms of hypoglycemia (low blood sugar) such as tremors and increased heart rate. (These symptoms are caused by activation of the adrenergic nervous system which labetalol blocks.) Therefore, diabetics taking medications that lower blood sugar such as insulin or oral anti-diabetic medications may need to increase the frequency with which they monitor their blood sugar.

Labetalol taken with calcium channel blockers such as diltiazem (Cardizem) or verapamil (Calan) may trigger an irregular heart rhythm or an increase in blood pressure.

Labetalol taken with tricyclic antidepressants such as amitriptyline (Elavil), imipramine (Tofranil), or nortriptyline (Pamelor) may lead to an increase in the tremor that is a side effect of the antidepressants.

If taken 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 concomitantly, more labetalol or less glutethimide may be needed.

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

PREGNANCY: It has not been determined if it is safe to use labetalol during pregnancy.

NURSING MOTHERS: Labetalol has been found 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.

SIDE EFFECTS AND PRECAUTIONS: The most common side effects of labetalol are fatigue, dizziness, headache, diarrhea, edema (fluid accumulation), dry eyes, and tingling of the scalp and skin. Postural hypotension (a rapid decrease in blood pressure when going from the seated 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.

Labetalol should be used with caution in the elderly and patients with asthma or cirrhosis.