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Alpha-adrenergic Antagonists

Description

This group of medicines is known as alpha-adrenergic blocking agents, alpha-blocking agents, or, more commonly, alpha-blockers. Alpha-blockers are used in the treatment of high blood pressure (hypertension). These agents work by dilating your blood vessels to reduce blood pressure. Some alpha-blockers are also used to treat benign prostatic hyperplasia (BPH) or glaucoma. They may also be used for other conditions as determined by your doctor.

Brand Names:

Aldomet® (Methyldopa)
Cardura® (Doxazosin)
Catapres®; Catapres-TTS®; Duraclon™ (Clonidine)
Dibenzyline® (Phenoxybenzamine)
Hylorel® (Guanadrel)
Hytrin® (Terazosin)
Minipress® (Prazosin)
Tenex® (Guanfacine)

Non-branded agents:
Guanabenz
Phentolamine
Reserpine

Alpha-adrenergic blocking agents are available only with your doctor's prescription, in the following dosage forms:

Clonidine:
       Injection, epidural solution, as hydrochloride [preservative free]
       Patch, transdermal [once-weekly patch]
       Tablets
Doxazosin:
       Tablets
Guanabenz:
       Tablets
Guanadrel:
       Tablets
Guanfacine:
       Tablets
Methyldopa:
       Injection, solution, as methyldopa hydrochloride
       Tablets
Phenoxybenzamine:
       Capsules
Phentolamine:
       Injection, powder for reconstitution
Prazosin:
       Capsules
Reserpine:
       Tablets
Terazosin:
       Capsules
       Tablets

Before Using This Medicine

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For the alpha-blockers, the following should be considered:

Allergies -- Tell your doctor if you have ever had any unusual or allergic reaction to the alpha-blocker medicine prescribed. Also tell your health care professional if you are allergic to any other substances, such as foods, preservatives, or dyes.

Pregnancy -- Before taking any of these medicines, make sure your doctor knows if you are pregnant or if you may become pregnant.

Breast-feeding -- Clonidine and reserpine enters breast milk, use caution. Methyldopa is safe to use during pregnancy. It is not known whether doxazosin, guanabenz, guanadrel, guanfacine, phenoxybenzamine, phentolamine, prazosin, and terazosin passes into breast milk.

Children -- Some of these medicines have been used in children and, in effective doses, have not been shown to cause different side effects or problems in children than they do in adults.

Older adults -- Some side effects are more likely to occur in the elderly, who are usually more sensitive to the effects of alpha-blockers.

Other medicines -- Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking or receiving a alpha-blocker it is especially important that your health care professional know if you are taking any of the following:

• ACE Inhibitors
• Beta-blockers
• Calcium-channel blockers
• Viagra® or other PDE-5 inhibitors
• NSAIDs – may reduce antihypertensive efficacy

Other medical problems -- The presence of other medical problems may affect the use of the alpha blockers. Make sure you tell your doctor if you have any other medical problems, especially:

• Allergy, history of (asthma, eczema, hay fever, hives), or
• Pre-existing CNS disease or depression, especially when taking clonidine
• Heart or blood vessel disease -- There is a risk of further decreased heart function; also, if treatment is stopped suddenly, unwanted effects may occur
• Kidney Disease
• Liver disease -- Effects of alpha-blockers may be increased because of slower removal from the body

Proper Use of This Medicine

For patients taking the extended-release capsule or tablet form of this medicine:

• Swallow the capsule or tablet whole.
• Do not crush, break or chew before swallowing.

To help you remember to take your medicine, try to get into the habit of taking it at the same time each day.

For patients taking this medicine for high blood pressure:

• In addition to the use of the medicine your doctor has prescribed, treatment for your high blood pressure may include weight control and care in the types of foods you eat, especially foods high in sodium. Your doctor will tell you which of these are most important for you. You should check with your doctor before changing your diet.
• Many patients who have high blood pressure will not notice any signs of the problem. In fact, many may feel normal. However, if high blood pressure is not treated, it can cause serious problems such as heart failure, blood vessel disease, stroke, or kidney disease.
• Remember that this medicine will not cure your high blood pressure but it does help control it. It is very important that you take your medicine exactly as directed, even if you feel well. You must continue to take it as directed if you expect to lower your blood pressure and keep it down. You may have to take high blood pressure medicine for the rest of your life. Also, it is very important to keep your appointments with your doctor, even if you feel well.

Dosing --

For clonidine:

Children:

Oral:

Hypertension: Initial: 5-10 mcg/kg/day in divided doses every 8-12 hours; increase gradually at 5- to 7-day intervals to 25 mcg/kg/day in divided doses every 6 hours; maximum: 0.9 mg/day

Clonidine tolerance test (test of growth hormone release from pituitary): 0.15 mg/m2 or 4 mcg/kg as single dose

ADHD (unlabeled use): Initial: 0.05 mg/day; increase every 3-7 days by 0.05 mg/day to 3-5 mcg/kg/day given in divided doses 3-4 times/day (maximum dose: 0.3-0.4 mg/day)

Epidural infusion: Pain management: Reserved for patients with severe intractable pain, unresponsive to other analgesics or epidural or spinal opiates: Initial: 0.5 mcg/kg/hour; adjust with caution, based on clinical effect

Adults:

Oral:

Acute hypertension (urgency): Initial 0.1-0.2 mg; may be followed by additional doses of 0.1 mg every hour, if necessary, to a maximum total dose of 0.6 mg

Hypertension: Initial dose: 0.1 mg twice daily, usual maintenance dose: 0.2-1.2 mg/day in 2-4 divided doses; maximum recommended dose: 2.4 mg/day

Nicotine withdrawal symptoms: 0.1 mg twice daily to maximum of 0.4 mg/day for 3-4 weeks

Transdermal: Hypertension: Apply once every 7 days; for initial therapy start with 0.1 mg and increase by 0.1 mg at 1- to 2-week intervals; dosages >0.6 mg do not improve efficacy

Epidural infusion: Pain management: Starting dose: 30 mcg/hour; titrate as required for relief of pain or presence of side effects; minimal experience with doses >40 mcg/hour; should be considered an adjunct to intraspinal opiate therapy

Elderly: Initial: 0.1 mg once daily at bedtime, increase gradually as needed

For doxazosin:

Oral:

Adults: 1 mg once daily in morning or evening; may be increased to 2 mg once daily. Thereafter titrate upwards, if needed, over several weeks, balancing therapeutic benefit with doxazosin-induced postural hypotension

Hypertension: Maximum dose: 16 mg/day

BPH: Maximum dose: 8 mg/day

Elderly: Initial: 0.5 mg once daily

For guanabenz:

Oral:

Adults: Initial: 4 mg twice daily; increase in increments of 4-8 mg/day every 1-2 weeks to a maximum of 32 mg twice daily.

For guanadrel:

Oral:

Adults: Initial: 10 mg/day (5 mg twice daily); adjust dosage weekly or monthly until blood pressure is controlled, usual dosage: 20-75 mg/day, given twice daily. For larger dosage, 3-4 times/day dosing may be needed.

Elderly: Initial: 5 mg once daily

For guanfacine:

Oral:

Adults:
Hypertension: 1 mg usually at bedtime, may increase if needed at 3- to 4-week intervals; 1 mg/day is most common dose

For methyldopa:

Children:

Oral: Initial: 10 mg/kg/day in 2-4 divided doses; increase every 2 days as needed to maximum dose of 65 mg/kg/day; do not exceed 3 g/day.

I.V.: 5-10 mg/kg/dose every 6-8 hours up to a total dose of 65 mg/kg/24 hours or 3 g/24 hours

Adults:

Oral: Initial: 250 mg 2-3 times/day; increase every 2 days as needed; usual dose 1-1.5 g/day in 2-4 divided doses; maximum dose: 3 g/day.

I.V.: 250-500 mg every 6-8 hours; maximum dose: 1 g every 6 hours

For phenoxybenzamine:

Oral:

Children: Initial: 0.2 mg/kg (maximum: 10 mg) once daily, increase by 0.2 mg/kg increments; usual maintenance dose: 0.4-1.2 mg/kg/day every 6-8 hours, higher doses may be necessary

Adults: Initial: 10 mg twice daily, increase by 10 mg every other day until optimum dose is achieved; usual range: 20-40 mg 2-3 times/day

For phentolamine:

Treatment of alpha-adrenergic drug extravasation: S.C.:

Children: 0.1-0.2 mg/kg diluted in 10 mL 0.9% sodium chloride infiltrated into area of extravasation within 12 hours

Adults: Infiltrate area with small amount of solution made by diluting 5-10 mg in 10 mL 0.9% sodium chloride within 12 hours of extravasation; do not exceed 0.1-0.2 mg/kg or 5 mg total

If dose is effective, normal skin color should return to the blanched area within 1 hour

Diagnosis of pheochromocytoma: I.M., I.V.:

Children: 0.05-0.1 mg/kg/dose, maximum single dose: 5 mg

Adults: 5 mg

Surgery for pheochromocytoma: Hypertension: I.M., I.V.:

Children: 0.05-0.1 mg/kg/dose given 1-2 hours before procedure; repeat as needed every 2-4 hours until hypertension is controlled; maximum single dose: 5 mg

Adults: 5 mg given 1-2 hours before procedure and repeated as needed every 2-4 hours

Hypertensive crisis: Adults: 5-20 mg

Treatment of pralidoxime-induced hypertension (unlabeled use): I.V.:

Children: 1 mg

Adults and Elderly: 5 mg

For prazosin:

Oral:

Children: Initial: 5 mcg/kg/dose (to assess hypotensive effects); usual dosing interval: every 6 hours; increase dosage gradually up to maximum of 25 mcg/kg/dose every 6 hours

Adults:

Hypertension: Initial: 1 mg/dose 2-3 times/day; usual maintenance dose: 3-15 mg/day in divided doses 2-4 times/day; maximum daily dose: 20 mg

Hypertensive urgency: 10-20 mg once, may repeat in 30 minutes

Raynaud's (unlabeled use): 0.5-3 mg twice daily

Benign prostatic hyperplasia (unlabeled use): 2 mg twice daily

For reserpine:

Oral:

Children: Hypertension: 0.01-0.02 mg/kg/24 hours divided every 12 hours; maximum dose: 0.25 mg/day (not recommended in children)

Adults:

Hypertension: 0.1-0.25 mg/day in 1-2 doses; initial: 0.5 mg/day for 1-2 weeks; maintenance: reduce to 0.1-0.25 mg/day;

Tardive dyskinesia/schizophrenia: Initial: 0.5 mg/day; usual range: 0.1-1 mg

Elderly: Initial: 0.05 mg once daily, increasing by 0.05 mg every week as necessary

For terazosin:

Oral: Adults:

Hypertension: Initial: 1 mg at bedtime; slowly increase dose to achieve desired blood pressure, up to 20 mg/day; usual dose: 1-5 mg/day

Dosage reduction may be needed when adding a diuretic or other antihypertensive agent; if drug is discontinued for greater than several days, consider beginning with initial dose and retitrate as needed; dosage may be given on a twice daily regimen if response is diminished at 24 hours and hypotensive is observed at 2-4 hours following a dose

Benign prostatic hyperplasia: Initial: 1 mg at bedtime, increasing as needed; most patients require 10 mg day; if no response after 4-6 weeks of 10 mg/day, may increase to 20 mg/day

Storage --

To store this medicine:

• Keep out of the reach of children.
• Store away from heat and direct light.
• Do not store in the bathroom, near the kitchen sink, or in other damp places. Heat or moisture may cause the medicine to break down.
• Do not keep outdated medicine or medicine no longer needed. Be sure that any discarded medicine is out of the reach of children.

Precautions While Using This Medicine

It is important that your doctor check your progress at regular visits. This is to make sure the medicine is working for you and to allow the dosage to be changed if needed.

Do not stop taking this medicine without first checking with your doctor. Your doctor may want you to reduce gradually the amount you are taking before stopping completely. Some conditions may become worse when the medicine is stopped suddenly, and the danger of heart attack is increased in some patients.

Make sure that you have enough medicine on hand to last through weekends, holidays, or vacations. You may want to carry an extra written prescription in your billfold or purse in case of an emergency. You can then have it filled if you run out of medicine while you are away from home.

Your doctor may want you to carry medical identification stating that you are taking this medicine.

Before having any kind of surgery (including dental surgery) or emergency treatment, tell the medical doctor or dentist in charge that you are taking this medicine.

This medicine may cause some people to become dizzy, drowsy, or lightheaded. Make sure you know how you react to this medicine before you drive, use machines, or do anything else that could be dangerous if you are dizzy or are not alert. If the problem continues or gets worse, check with your doctor.

Before you have any medical tests, tell the doctor in charge that you are taking this medicine. The results of some tests may be affected by this medicine.

For patients taking this medicine for high blood pressure :

• Do not take other medicines unless they have been discussed with your doctor. This especially includes over-the-counter (nonprescription) medicines for appetite control, asthma, colds, cough, hay fever, or sinus problems since they may tend to increase your blood pressure.

Side Effects of This Medicine

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• Less common
  • Cold hands and feet; mental depression; palpitations; swelling of ankles, feet, and/or lower legs
     
• Rare
  • Chest pain; confusion (especially in elderly patients); dizziness or lightheadedness when getting up from a lying or sitting position; fever and sore throat; hallucinations (seeing, hearing, or feeling things that are not there); irregular heartbeat; red, scaling, or crusted skin; skin rash; unusual bleeding and bruising; sexual dysfunction; syncope; atrial fibrillation; priapism
     
• Signs and symptoms of overdose (in the order in which they may occur)
  • Hypotension, drowsiness, and shock

Other side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. However, check with your doctor if any of the following side effects continue or are bothersome:

• More common
  • Decreased sexual ability; dizziness or lightheadedness; drowsiness (slight); trouble sleeping; unusual tiredness or weakness
     
• Less common or rare
  • Anxiety and/or nervousness; constipation; diarrhea; dry, sore eyes; itching of skin; nausea or vomiting; nightmares and vivid dreams; stomach discomfort; stuffy nose

Although not all of the side effects listed above have been reported for all of these medicines, they have been reported for at least one of them. Since all of the alpha-adrenergic blocking agents are very similar, any of the above side effects may occur with any of these medicines. However, they may be more or less common with some agents than with others.

• After you have been taking a alpha-blocker for a while, it may cause unpleasant or even harmful effects if you stop taking it too suddenly.

Other side effects not listed above may also occur in some patients. If you notice any other effects, check with your doctor.