US Brand Names
Canadian Brand Names
Prazosin (PRA-zoe-sin) belongs to the general class of medicines called antihypertensives. It is used to treat high blood pressure (hypertension).
High blood pressure adds to the work load of the heart and arteries. If it continues for a long time, the heart and arteries may not function properly. This can damage the blood vessels of the brain, heart, and kidneys, resulting in a stroke, heart failure, or kidney failure. High blood pressure may also increase the risk of heart attacks. These problems may be less likely to occur if blood pressure is controlled.
Prazosin works by relaxing blood vessels so that blood passes through them more easily. This helps to lower blood pressure.
Prazosin may also be used for other conditions as determined by your doctor.
Prazosin is available only with your doctor's prescription, in the following dosage forms:
• Capsules (U.S.)
• Tablets (Canada)
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 prazosin, the following should be considered:
Tell your doctor if you have ever had any unusual or allergic reaction to prazosin, doxazosin, or terazosin. Also tell your health care professional if you are allergic to any other substance, such as foods, preservatives, or dyes.
Limited use of prazosin to control high blood pressure in pregnant women has not shown that prazosin causes birth defects or other problems. Studies in animals given many times the highest recommended human dose of prazosin also have not shown that prazosin causes birth defects. However, in rats given many times the highest recommended human dose, lower birth weights were seen.
Prazosin passes into breast milk in small amounts. However, it has not been reported to cause problems in nursing babies.
Studies on this medicine have been done only in adult patients, and there is no specific information comparing use of prazosin in children with use in other age groups.
Dizziness, lightheadedness, or fainting (especially when getting up from a lying or sitting position) may be more likely to occur in the elderly, who are more sensitive to the effects of prazosin. In addition, prazosin may reduce tolerance to cold temperatures in elderly patients.
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.
Other medical problems
The presence of other medical problems may affect the use of prazosin. Make sure you tell your doctor if you have any other medical problems, especially:
• Angina (chest pain) or
• Heart disease (severe)-Prazosin may make these conditions worse
• Kidney disease-Possible increased sensitivity to the effects of prazosin
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. It is very important that you take your medicine exactly as directed and that you keep your appointments with your doctor even if you feel well.
• Remember that prazosin will not cure your high blood pressure but it does help control it. Therefore, 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 . If high blood pressure is not treated, it can cause serious problems such as heart failure, blood vessel disease, stroke, or kidney disease.
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 prazosin 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 prazosin. If your dose is different, do not change it unless your doctor tells you to do so.
The number of capsules or tablets that you take depends on the strength of the medicine.
• For oral dosage form (capsules or tablets):
o For high blood pressure:
§ Adults-At first, 0.5 or 1 milligram (mg) two or three times a day. Then, your doctor will slowly increase your dose to 6 to 15 mg a day. This is divided into two or three doses.
§ Children-Dose is based on body weight and must be determined by your doctor. The usual dose is 50 to 400 micrograms (mcg) (0.05 to 0.4 mg) per kilogram of body weight (22.73 to 181.2 mcg per pound [0.023 to 0.18 mg per pound]) a day. This is divided into two or three doses.
If you miss a dose of this medicine, 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.
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.
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 make prazosin less effective.
Dizziness, lightheadedness, or sudden fainting may occur after you take this medicine, especially when you get up from a lying or sitting position. These effects are more likely to occur when you take the first dose of this medicine. Taking the first dose at bedtime may prevent problems. However, be especially careful if you need to get up during the night . These effects may also occur with any doses you take after the first dose. Getting up slowly may help lessen this problem. If you feel dizzy, lie down so that you do not faint . Then sit for a few moments before standing to prevent the dizziness from returning.
The dizziness, lightheadedness, or fainting is 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 to limit the amount of alcohol you drink. Also, use extra care during exercise or hot weather or if you must stand for a long time .
Prazosin may cause some people to become drowsy or less alert than they are normally. 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, drowsy, or are not alert . After you have taken several doses of this medicine, these effects should lessen.
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:
Dizziness or lightheadedness, especially when getting up from a lying or sitting position; fainting (sudden).
Loss of bladder control; pounding heartbeat; swelling of feet or lower legs.
Chest pain; painful inappropriate erection of penis (continuing); shortness of breath.
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:
Drowsiness; headache; lack of energy.
Dryness of mouth; nervousness; unusual tiredness or weakness.
Frequent urge to urinate; nausea.
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 these uses are not included in product labeling, prazosin is used in certain patients with the following medical conditions:
• Congestive heart failure
• Ergot alkaloid poisoning
• Raynaud's disease
• Benign enlargement of the prostate
For patients taking this medicine for benign enlargement of the prostate :
• Prazosin will not shrink the size of your prostate, but it does help to relieve the symptoms.
Other than the above information, there is no additional information relating to proper use, precautions, or side effects for these uses.
August 29, 1998