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Doxazosin (dox-AY-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 workload 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.
Doxazosin works by relaxing blood vessels so that blood passes through them more easily. This helps to lower blood pressure.
Doxazosin is also used to treat benign (noncancerous) enlargement of the prostate (benign prostatic hyperplasia [BPH]). Benign enlargement of the prostate is a problem that can occur in men as they get older. The prostate gland is located below the bladder. As the prostate gland enlarges, certain muscles in the gland may become tight and get in the way of the tube that drains urine from the bladder. This can cause problems in urinating, such as a need to urinate often, a weak stream when urinating, or a feeling of not being able to empty the bladder completely.
Doxazosin helps relax the muscles in the prostate and the opening of the bladder. This may help increase the flow of urine and/or decrease the symptoms. However, doxazosin will not shrink the prostate. The prostate may continue to get larger. This may cause the symptoms to become worse over time. Therefore, even though doxazosin may lessen the problems caused by enlarged prostate now, surgery still may be needed in the future.
Doxazosin is available only with your doctor's prescription, in the following dosage form:
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 doxazosin, the following should be considered:
Tell your doctor if you have ever had any unusual or allergic reaction to doxazosin, prazosin, or terazosin. Also tell your health care professional if you are allergic to any other substances, such as foods, preservatives, or dyes.
Doxazosin has not been studied in pregnant women. However, studies in rabbits have shown that doxazosin given at very high doses may cause death of the fetus. Before taking this medicine, make sure your doctor knows if you are pregnant or if you may become pregnant.
It is not known whether doxazosin passes into breast milk. However, doxazosin passes into the milk of lactating rats. Although most medicines pass into breast milk in small amounts, many of them may be used safely while breast-feeding. Mothers who are taking this medicine and who wish to breast-feed should discuss this with their doctor.
Studies on this medicine have been done only in adult patients, and there is no specific information comparing use of doxazosin in children with use in other age groups.
Dizziness, lightheadedness, or fainting may be especially likely to occur in elderly patients with high blood pressure, because these patients are usually more sensitive than younger adults to the effects of doxazosin.
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 using any other prescription or nonprescription (over-the-counter [OTC]) medicine.
Other medical problems
The presence of other medical problems may affect the use of doxazosin. Make sure you tell your doctor if you have any other medical problems, especially:
• Kidney disease-Possible increased sensitivity to the effects of doxazosin
• Liver disease-The effects of doxazosin may be increased, which may increase the chance of side effects
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. 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 doxazosin 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.
For patients taking this medicine for benign enlargement of the prostate :
• Remember that doxazosin will not shrink the size of your prostate but it does help to relieve the symptoms of this condition. You may still need to have surgery later.
• It may take up to 2 weeks before your symptoms improve.
The dose of doxazosin 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 doxazosin. If your dose is different, do not change it unless your doctor tells you to do so.
The number of tablets that you take depends on the strength of the medicine.
• For oral dosage form (tablets):
o For benign enlargement of the prostate:
§ Adults-At first, 1 milligram (mg) once a day, in the morning or in the evening. Your doctor may increase your dose slowly up to 8 mg once a day.
o For high blood pressure:
§ Adults-1 mg once a day to start. Your doctor may increase your dose slowly to as much as 16 mg once a day.
§ Children-Use and dose must be determined by your doctor.
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.
If you miss several doses, call your doctor to see at what dose you should start again.
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. This is especially important for elderly patients, who may be more sensitive to the effects of 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.
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 sudden 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 .
Doxazosin 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.
The possibility of priapism, a painful or prolonged erection of the penis, is a rare side effect that can occur when taking doxazosin and must have immediate medical attention.
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.
Dizziness or lightheadedness when getting up from a lying or sitting position; fainting (sudden); fast and pounding heartbeat; irregular heartbeat; shortness of breath; swelling of feet or lower legs.
Painful or prolonged erection of the penis (called priapism), although extremely rare, must have immediate medical attention. If painful or prolonged erection occurs, call your doctor or go to an emergency room as soon as possible.
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:
Headache; unusual tiredness.
Nausea; nervousness, restlessness, unusual irritability; runny nose; sleepiness or drowsiness.
Other side effects not listed above may also occur in some patients. If you notice any other effects, check with your doctor.
May 21, 1999