Labetalol: 7 things you should know
Medically reviewed by C. Fookes, BPharm Last updated on Aug 30, 2019.
1. How it works
- Labetalol works on both alpha and beta receptors in the heart to lower blood pressure and slow heart rate.
- Labetalol belongs to the class of drugs known as beta blockers. It has selective alpha-1 adrenergic receptor blocking activity and nonselective beta-blocking activity.
- Used to lower high blood pressure (hypertension).
- The injectable form of labetalol is only used to treat severe hypertension.
- Only mildly slows heart rate.
- Blunts the increase in blood pressure and heartrate that occurs during exercise without affecting how well the lungs are perfused with blood.
- Use at recommended dosages does not appear to have a detrimental effect on kidney function in people with normal kidney function.
- Labetalol may be used alone or in addition to other antihypertensives (such as diuretics).
- Available in an injectable form and as a tablet.
- Brand names include Normodyne and Trandate.
- Generic labetalol is available.
If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:
- Dizziness, nausea, fatigue, tingling of the scalp or skin, and fluid retention.
- Labetalol lowers blood pressure more when standing than when sitting or lying down. This may cause postural hypotension (a noticeable drop in blood pressure when going from a sitting to a standing position). Symptoms may include dizziness.
- Labetalol is not suitable for people with certain heart conditions including cardiac failure, slow heartbeat (bradycardia), peripheral circulatory disorders (conditions that cause reduced blood flow to the hands or feet), and extremely low blood pressure.
- Sudden discontinuation of labetalol has been associated with an exacerbation of angina, and occasionally heart attacks and arrhythmias. The dosage needs to be tapered off slowly.
- Labetalol can cause a narrowing of the airways (bronchoconstriction) in people with asthma or other respiratory diseases. Avoid.
- Elderly people may be more sensitive to the effects of labetalol. Generally, lower maintenance dosages are needed.
- Rarely, may cause potentially fatal liver damage.
- Can mask symptoms of hypoglycemia (such as a fast heartbeat), so should be used with caution in people with diabetes. Insulin dosages may also need adjusting.
- May cause an intraoperative floppy iris syndrome during cataract surgery.
- May interact with some medications including other medications used for the treatment of arrhythmias or angina.
- May interfere with some lab tests including amphetamine tests.
Notes: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. For a complete list of all side effects, click here.
- May be taken with or without food.
- Labetalol tablets are usually given at a dosage of 100mg twice a day. The dosage is slowly increased as needed until an optimum effect on blood pressure is achieved; this maintenance dosage may differ from person-to-person. Take your tablets exactly as directed by your doctor.
- Should always be used as part of a comprehensive cardiovascular risk reduction program which includes diabetes management, smoking cessation, exercise, and other drug therapies. May be used in addition to other blood pressure-lowering medicines.
- Seek medical advice immediately if shortness of breath develops.
- Seek medical advice if any new numbness, pain, skin color changes or reduced sensitivity occurs in fingers or toes.
- Sudden discontinuation has been associated with an exacerbation of angina, and sometimes myocardial infarction (heart attack) or ventricular arrhythmias. If you need to discontinue labetalol, your doctor will advise how to do this slowly over one to two weeks.
- If you have diabetes, labetalol may mask some of the symptoms of low blood sugar, such as a fast heartbeat.
- Tell all health professionals that you take labetalol as it may interfere with some procedures.
6. Response and Effectiveness
- Peak concentrations of labetalol tablets are reached after one to two hours of oral administration. Labetalol tablets need to be given twice a day.
- Peak concentrations are reached within 5 minutes of labetalol injection. Blood pressure-lowering effects increase with higher dosages. An average lowering of blood pressure of 11/7 mmHg was reported with an initial dosage of 0.25 mg/kg labetalol injection. Blood pressure-lowering effects last an average of 16 to 18 hours.
Medicines that interact with labetalol may either decrease its effect, affect how long it works for, increase side effects, or have less of an effect when taken with labetalol. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.
Common medications that may interact with labetalol include:
- antidepressants, such as fluoxetine, paroxetine, St John’s Wort, and monoamine oxidase inhibitors. Tricyclic antidepressants (such as amitriptyline, imipramine, and nortriptyline) may increase the risk of tremor
- antifungals, such as terbinafine
- antihistamines, such as diphenhydramine
- antimalaria agents, such as hydroxychloroquine
- bupropion, which may be used for the treatment of depression and as a stop-smoking aid
- fingolimod, which may be used for the treatment of multiple sclerosis
- HIV medications such as ritonavir
- indigestion and heartburn medications, such as cimetidine and ranitidine
- some medications used to treat mental illness, such as thioridazine
- some heart medications, such as amiodarone, clonidine, digoxin, diltiazem, propafenone, quinidine, and verapamil
- other medications including celecoxib, clonidine, hydralazine, and rifampicin
- NSAIDs, such as diclofenac, ibuprofen, and indomethacin, may decrease the blood pressure-lowering capabilities of labetalol.
People taking oral medications for diabetes may need to talk to their doctor about adjusting the dose of their diabetes medicine. Labetalol may counteract the effect of respiratory medicines such as albuterol.
Note that this list is not all-inclusive and includes only common medications that may interact with labetalol. You should refer to the prescribing information for labetalol for a complete list of interactions.
Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use labetalol only for the indication prescribed.
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