Medically reviewed on June 7, 2018
Commonly used brand name(s)
In the U.S.
Available Dosage Forms:
Therapeutic Class: Cardiovascular Agent
Pharmacologic Class: Alpha-Adrenergic Blocker
Uses For This Medicine
Phenoxybenzamine 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.
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 phenoxybenzamine, the following should be considered:
Tell your doctor if you have ever had any unusual or allergic reaction to phenoxybenzamine or any other medicines. Also tell your health care professional if you have any other types of allergies, such as to foods, dyes, preservatives, or animals. For non-prescription products, read the label or package ingredients carefully.
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.
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.
|All Trimesters||C||Animal studies have shown an adverse effect and there are no adequate studies in pregnant women OR no animal studies have been conducted and there are no adequate studies in pregnant women.|
There are no adequate studies in women for determining infant risk when using this medication during breastfeeding. Weigh the potential benefits against the potential risks before taking this medication while breastfeeding.
Interactions with 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 phenoxybenzamine, it is especially important that your healthcare professional know if you are taking any of the medicines listed below. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.
Using phenoxybenzamine with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.
Using phenoxybenzamine with any of the following medicines may cause an increased risk of certain side effects, but using both drugs may be the best treatment for you. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.
Interactions with Food/Tobacco/Alcohol
Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Using alcohol or tobacco with certain medicines may also cause interactions to occur. Discuss with your healthcare professional the use of your medicine with food, alcohol, or tobacco.
Other Medical Problems
The presence of other medical problems may affect the use of phenoxybenzamine. Make sure you tell your doctor if you have any other medical problems, especially:
- 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
Proper Use of This Medicine
To help you remember to take your medicine, try to get into the habit of taking it at the same time each day.
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.
The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.
- 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.
- For high blood pressure caused by pheochromocytoma:
If you miss a dose of phenoxybenzamine, take it as soon as possible. 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.
Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Keep from freezing.
Keep out of the reach of children.
Do not keep outdated medicine or medicine no longer needed.
Precautions While Using This Medicine
It is important that your doctor check your progress at regular visits to make sure that phenoxybenzamine 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 phenoxybenzamine.
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 phenoxybenzamine 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 phenoxybenzamine, 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 phenoxybenzamine.
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.
This Medicine Side Effects
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. Although not all of these side effects may occur, if they do occur they may need medical attention.
Some 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. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:
- Dizziness or lightheadedness, especially when getting up from a lying or sitting position
- fast heartbeat
- pinpoint pupils
- stuffy nose
- dryness of mouth
- lack of energy
- sexual problems in males
- unusual tiredness or weakness
Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.
Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.
See also: Side effects (in more detail)
Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.
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