In the U.S.—

• Antihypertensive, pheochromocytoma
• Benign prostatic hypertrophy therapy

Phenoxybenzamine (fen-ox-ee-BEN-za-meen) belongs to the general class of medicines called antihypertensives. It is used to treat high blood pressure (hypertension) due to a disease called pheochromocytoma.

Phenoxybenzamine blocks the effects of certain chemicals in the body. When these chemicals are present in large amounts, they cause high blood pressure.

Phenoxybenzamine may also be used for other conditions as determined by your doctor.

Phenoxybenzamine is available only with your doctor's prescription, in the following dosage form:

Oral
• Capsules (U.S.)

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 phenoxybenzamine, the following should be considered:

Allergies—Tell your doctor if you have ever had any unusual or allergic reaction to phenoxybenzamine. Also, tell your health care professional if you are allergic to any other substances, such as foods, preservatives, or dyes.

Pregnancy—Phenoxybenzamine has not been studied in pregnant women or animals. Make sure your doctor knows if you are pregnant or if you may become pregnant before taking phenoxybenzamine.

Breast-feeding—It is not known whether phenoxybenzamine passes into breast milk. However, this medicine has not been reported to cause problems in nursing babies.

Children—Although there is no specific information about the use of phenoxybenzamine in children, it is not expected to cause different side effects or problems in children than it does in adults.

Older adults—Dizziness or lightheadedness may be more likely to occur in the elderly, who are more sensitive to the effects of phenoxybenzamine. In addition, phenoxybenzamine may reduce tolerance to cold temperatures in elderly patients.

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. Tell your health care professional if you are taking any other prescription or nonprescription (over-the-counter [OTC]) medicine.

• Angina (chest pain) or
• Heart or blood vessel disease—Some kinds may be worsened by phenoxybenzamine

• Kidney disease—Effects may be increased

• Lung infection—Symptoms such as stuffy nose may be worsened

• Recent heart attack or stroke—Lowering blood pressure may make problems resulting from stroke or heart attack worse

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

Dosing—

The dose of phenoxybenzamine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of phenoxybenzamine. If your dose is different, do not change it unless your doctor tells you to do so.

• For oral dosage form (capsules):
  • For high blood pressure caused by pheochromocytoma:
    • Adults—At first, 10 milligrams (mg) two times a day. Then, your doctor may increase your dose to 20 to 40 mg two or three times a day.
    • Children—Dose is based on body weight and must be determined by your doctor. The usual starting dose is 0.2 mg per kilogram (kg) (0.09 mg per pound) of body weight taken once a day. Then, your doctor may increase your dose to 0.4 to 1.2 mg per kg (0.18 to 0.55 mg per pound) of body weight a day. This is divided into three or four doses.

Missed dose—

If you miss a dose of this medicine, take it as soon as you remember. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.

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.

It is important that your doctor check your progress at regular visits to make sure that this medicine is working properly and to check for unwanted effects.

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 interfere with the effects of this medicine.

Phenoxybenzamine may cause some people to become dizzy, drowsy, or less alert than they are normally. This is more likely to happen when you begin to take it or when you increase the amount of medicine you are taking. 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 not alert.

Dizziness, lightheadedness, or fainting may occur, especially when you get up from a lying or sitting position. Getting up slowly may help, but if the problem continues or gets worse, check with your doctor.

The dizziness, lightheadedness, or fainting is also more likely to occur if you drink alcohol, stand for a long time, exercise, or if the weather is hot. While you are taking this medicine, be careful in the amount of alcohol you drink. Also, use extra care during exercise or hot weather or if you must stand for a long time.

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

Phenoxybenzamine may cause dryness of the mouth, nose, and throat. For temporary relief of mouth dryness, use sugarless candy or gum, melt bits of ice in your mouth, or use a saliva substitute. However, if dry mouth continues for more than 2 weeks, check with your medical doctor or dentist. Continuing dryness of the mouth may increase the chance of dental disease, including tooth decay, gum disease, and fungus infections.

In rats and mice, phenoxybenzamine has been found to increase the risk of development of malignant tumors. It is not known if phenoxybenzamine increases the chance of tumors in humans.

Along with its needed effects, a medicine may cause some unwanted effects. The following side effects may go away as your body adjusts to the medicine. However, check with your doctor if any of these effects continue or are bothersome:

• More common
  • Dizziness or lightheadedness, especially when getting up from a lying or sitting position;  fast heartbeat;  pinpoint pupils;  stuffy nose 
  
  

• Less common
  • Confusion;  drowsiness;  dryness of mouth;  headache;  lack of energy;  sexual problems in males ;  unusual tiredness or weakness 
  
  

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

Once a medicine has been approved for marketing for a certain use, experience may show that it is also useful for other medical problems. Although this use is not included in product labeling, phenoxybenzamine is used in certain patients with the following medical condition:

• Benign prostatic hypertrophy

Other than the above information, there is no additional information relating to proper use, precautions, or side effects for this use.