Prazosin

Serious side effects have been reported including:

• Extremely rarely, prazosin and similar medications have caused painful erection of the penis, sustained for hours and unrelieved by sexual intercourse or masturbation. This condition, known medically as priapism, is serious, and if untreated it can be followed by permanent inability to have an erection. If you have a prolonged abnormal erection, call your doctor or go to an emergency room as soon as possible.
• Tell your surgeon if you take or have taken prazosin and plan to have surgery for cataracts (clouding of the eye). During cataract surgery, a condition called Intraoperative Floppy Iris Syndrome (IFIS) can happen if you take or have taken prazosin.
• Prazosin lowers blood pressure and may cause dizziness or fainting, especially when you first start taking it, or when you start taking it again. Call your doctor if you have severe dizziness or feel like you might pass out.

Prazosin can cause drowsiness. Do not drive or operate heavy machinery until you know how prazosin affects you.

Do not take prazosin if you:

• are allergic to prazosin or any inactive ingredient in prazosin
• are allergic to any of the medications related to prazosin such as alfuzosin (Uroxatral), doxazosin (Cardura), and terazosin (Hytrin)

Take prazosin exactly as prescribed. Follow the directions on your prescription label carefully. Your doctor will likely start you on a low dose and gradually increase the dose as necessary.

The recommended starting prazosin dose is 1 mg two or three times a day. Your doctor may gradually increase your dose until your maintenance dose is reached.

Daily doses commonly range between 6 mg and 15 mg.

Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Call your doctor at once if you have a serious side effect such as:

• fast or pounding heartbeats or fluttering in your chest;

• feeling like you might pass out;

• trouble breathing;

• swelling in your hands, ankles, or feet; or

• penis erection that is painful or lasts 4 hours or longer.

Less serious side effects may include:

• mild dizziness;

• weakness, tired feeling, drowsiness;

• headache; or

• nausea.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

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:

Allergies

Tell your doctor if you have ever had any unusual or allergic reaction to prazosin 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.

Pediatric

Appropriate studies have not been performed on the relationship of age to the effects of prazosin in the pediatric population. Safety and efficacy have not been established.

Geriatric

No information is available on the relationship of age to the effects of prazosin in geriatric patients.

Pregnancy

Breast Feeding

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 prazosin, 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 prazosin 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.

• Asenapine
• Tadalafil

Using prazosin 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.

• Acebutolol
• Alprenolol
• Atenolol
• Betaxolol
• Bevantolol
• Bisoprolol
• Bucindolol
• Carteolol
• Carvedilol
• Celiprolol
• Dilevalol
• Esmolol
• Labetalol
• Levobunolol
• Mepindolol
• Metipranolol
• Metoprolol
• Nadolol
• Nebivolol
• Oxprenolol
• Penbutolol
• Pindolol
• Propranolol
• Sildenafil
• Sotalol
• Talinolol
• Tertatolol
• Timolol
• Vardenafil

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 prazosin. Make sure you tell your doctor if you have any other medical problems, especially:

• Angina (chest pain) or
• Heart disease, severe or
• Postural hypotension (low blood pressure)—Use with caution. May make these conditions worse.

• Cataract surgery—An eye problem called Intraoperative Floppy Iris Syndrome (IFIS) has occurred in patients who are taking or who have recently taken prazosin when they are having cataract surgery. You should tell your ophthalmologist (eye doctor) before your surgery if you are taking prazosin.

• Kidney disease—Use with caution. The effects may be increased because of slower removal of the medicine from the body.

In addition to the use of prazosin, treatment for your high blood pressure may include weight control and changes in the types of foods you eat, especially foods high in sodium (salt). 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 symptoms of the condition. In fact, many patients 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. 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.

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 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 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:
    • Adults—At first, 1 milligram (mg) two or three times a day. Your doctor will slowly increase your dose as needed. However, the dose is usually not more than 20 mg per day.
    • Children—Use and dose must be determined by your doctor.

Missed Dose

If you miss a dose of prazosin, 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.

Storage

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.

Ask your healthcare professional how you should dispose of any medicine you do not use.

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

Dizziness, lightheadedness, or fainting may occur, especially when you get up from a lying or sitting position suddenly. Getting up slowly may help. These symptoms are more likely to occur when you begin taking prazosin, or when the dose is increased.

You may also have dizziness, lightheadedness, or fainting if you drink alcohol, stand for a long time, exercise or if the weather is hot. While you are taking prazosin, be careful to limit the amount of alcohol you drink. Also, use extra care during exercise or hot weather.

Prazosin may cause some people to become dizzy, drowsy, or less alert than they are normally. Make sure you know how you react to prazosin before you drive, use machines, or do anything else that could be dangerous if you are dizzy, drowsy, or are not alert.

Make sure any doctor or dentist who treats you knows that you are using prazosin. prazosin may affect the results of certain medical tests.

Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements.

If you are a man and experience a prolonged or painful erection for 4 hours or more, contact your doctor immediately. This condition may require prompt medical treatment to prevent serious and permanent damage to your penis.

The exact mechanism of the hypotensive action of Prazosin is unknown. Prazosin causes a decrease in total peripheral resistance and was originally thought to have a direct relaxant action on vascular smooth muscle. Recent animal studies, however, have suggested that the vasodilator effect of Prazosin is also related to blockade of postsynaptic alpha-adrenoceptors. The results of dog forelimb experiments demonstrate that the peripheral vasodilator effect of Prazosin is confined mainly to the level of the resistance vessels (arterioles). Unlike conventional alpha-blockers, the antihypertensive action of Prazosin is usually not accompanied by a reflex tachycardia. Tolerance has not been observed to develop in long term therapy.

Hemodynamic studies have been carried out in man following acute single dose administration and during the course of long term maintenance therapy. The results confirm that the therapeutic effect is a fall in blood pressure unaccompanied by a clinically significant change in cardiac output, heart rate, renal blood flow and glomerular filtration rate. There is no measurable negative chronotropic effect.

In clinical studies to date, Prazosin hydrochloride has not increased plasma renin activity.

In man, blood pressure is lowered in both the supine and standing positions. This effect is most pronounced on the diastolic blood pressure.

Following oral administration, human plasma concentrations reach a peak at about three hours with a plasma half-life of two to three hours. The drug is highly bound to plasma protein. Bioavailability studies have demonstrated that the total absorption relative to the drug in a 20% alcoholic solution is 90%, resulting in peak levels approximately 65% of that of the drug in solution. Animal studies indicate that Prazosin hydrochloride is extensively metabolized, primarily by demethylation and conjugation, and excreted mainly via bile and feces. Less extensive human studies suggest similar metabolism and excretion in man.

In clinical studies in which lipid profiles were followed, there were generally no adverse changes noted between pre- and post-treatment lipid levels.

Prazosin hydrochloride capsules are indicated for the treatment of hypertension, to lower blood pressure. Lowering blood pressure reduces the risk of fatal and nonfatal cardiovascular events, primarily strokes and myocardial infarctions. These benefits have been seen in controlled trials of antihypertensive drugs from a wide variety of pharmacologic classes, including this drug.

Control of high blood pressure should be part of comprehensive cardiovascular risk management, including, as appropriate, lipid control, diabetes management, antithrombotic therapy, smoking cessation, exercise, and limited sodium intake. Many patients will require more than one drug to achieve blood pressure goals. For specific advice on goals and management, see published guidelines, such as those of the National High Blood Pressure Education Program's Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC).

Numerous antihypertensive drugs, from a variety of pharmacologic classes and with different mechanisms of action, have been shown in randomized controlled trials to reduce cardiovascular morbidity and mortality, and it can be concluded that it is blood pressure reduction, and not some other pharmacologic property of the drugs, that is largely responsible for those benefits. The largest and most consistent cardiovascular outcome benefit has been a reduction in the risk of stroke, but reductions in myocardial infarction and cardiovascular mortality also have been seen regularly.

Elevated systolic or diastolic pressure causes increased cardiovascular risk, and the absolute risk increase per mmHg is greater at higher blood pressures, so that even modest reductions of severe hypertension can provide substantial benefit. Relative risk reduction from blood pressure reduction is similar across populations with varying absolute risk, so the absolute benefit is greater in patients who are at higher risk independent of their hypertension (for example, patients with diabetes or hyperlipidemia), and such patients would be expected to benefit from more aggressive treatment to a lower blood pressure goal.

Some antihypertensive drugs have smaller blood pressure effects (as monotherapy) in black patients, and many antihypertensive drugs have additional approved indications and effects (e.g., on angina, heart failure, or diabetic kidney disease). These considerations may guide selection of therapy.

Prazosin hydrochloride capsules can be used alone or in combination with other antihypertensive drugs such as diuretics or beta-adrenergic blocking agents.

As with all alpha-blockers, Prazosin hydrochloride capsules may cause syncope with sudden loss of consciousness. In most cases, this is believed to be due to an excessive postural hypotensive effect, although occasionally the syncopal episode has been preceded by a bout of severe tachycardia with heart rates of 120–160 beats per minute. Syncopal episodes have usually occurred within 30 to 90 minutes of the initial dose of the drug; occasionally, they have been reported in association with rapid dosage increases or the introduction of another antihypertensive drug into the regimen of a patient taking high doses of Prazosin hydrochloride capsules. The incidence of syncopal episodes is approximately 1% in patients given an initial dose of 2 mg or greater. Clinical trials conducted during the investigational phase of this drug suggest that syncopal episodes can be minimized by limiting the initial dose of the drug to 1 mg, by subsequently increasing the dosage slowly, and by introducing any additional antihypertensive drugs into the patient's regimen with caution (see DOSAGE AND ADMINISTRATION). Hypotension may develop in patients given Prazosin hydrochloride capsules who are also receiving a beta-blocker such as propranolol.

If syncope occurs, the patient should be placed in the recumbent position and treated supportively as necessary. This adverse effect is self-limiting and in most cases does not recur after the initial period of therapy or during subsequent dose titration.

Patients should always be started on the 1 mg capsules of Prazosin hydrochloride. The 2 and 5 mg capsules are not indicated for initial therapy.

More common than loss of consciousness are the symptoms often associated with lowering of the blood pressure, namely, dizziness and lightheadedness. The patient should be cautioned about these possible adverse effects and advised what measures to take should they develop. The patient should also be cautioned to avoid situations where injury could result should syncope occur during the initiation of Prazosin hydrochloride therapy.

Priapism

Prolonged erections and priapism have been reported with alpha-1 blockers including Prazosin in post marketing experience. In the event of an erection that persists longer than 4 hours, seek immediate medical assistance. If priapism is not treated immediately, penile tissue damage and permanent loss of potency could result.

NDC 59762-5310-1
90 Capsules

GREENSTONE® BRAND

Prazosin
hydrochloride
capsules

1 mg*

Rx only

• Minipress

Competitively inhibits postsynaptic alpha-adrenergic receptors which results in vasodilation of veins and arterioles and a decrease in total peripheral resistance and blood pressure

Distribution

Vd: 0.5 L/kg

Metabolism

Extensively hepatic via demethylation and conjugation

Excretion

Feces; urine (6% to 10% as unchanged drug)

Post-traumatic stress disorder (PTSD) related nightmares and sleep disruption

Data from three double-blind, placebo-controlled trials, supports the use of prazosin in reducing trauma nightmares and improving sleep disruption in both veteran combat related and civilian noncombat related chronic PTSD [Raskind 2003], [Raskind 2007], [Taylor 2008]. Additional trials may be necessary to further define the role of prazosin in this condition.

Based on the American Psychiatric Association practice guidelines for the treatment of acute stress disorder and posttraumatic stress disorder, prazosin appears effective for the management of trauma-related nightmares and sleep disruption associated with PTSD. Similarly, based on the World Federation of Societies of Biological Psychiatry (WFSBP) guidelines for the treatment of anxiety, obsessive-compulsive and post-traumatic stress disorder, prazosin may reduce nightmares and be an alternative therapy for treatment-resistant cases.

Raynaud phenomenon

Data from a limited number of patients in four double-blind, placebo-controlled trials and an open-label dose response trial suggest that prazosin may be beneficial for the treatment of Raynaud phenomenon [Nielson 1983], [Russell 1985], [Surwit 1984], [Wollersheim 1988], [Wollersheim 1986]. Additional data may be necessary to further define the role of prazosin in this condition.

There are no dosage adjustments provided in the manufacturer’s labeling.

Alpha-/Beta-Agonists: Alpha1-Blockers may diminish the vasoconstricting effect of Alpha-/Beta-Agonists. Similarly, Alpha-/Beta-Agonists may antagonize Alpha1-Blocker vasodilation. Monitor therapy

Alpha1-Agonists: Alpha1-Blockers may diminish the vasoconstricting effect of Alpha1-Agonists. Similarly, Alpha1-Agonists may antagonize Alpha1-Blocker vasodilation. Monitor therapy

Alpha1-Blockers: May enhance the antihypertensive effect of other Alpha1-Blockers. Avoid combination

Amifostine: Blood Pressure Lowering Agents may enhance the hypotensive effect of Amifostine. Management: When amifostine is used at chemotherapy doses, blood pressure lowering medications should be withheld for 24 hours prior to amifostine administration. If blood pressure lowering therapy cannot be withheld, amifostine should not be administered. Consider therapy modification

Amphetamines: May diminish the antihypertensive effect of Antihypertensive Agents. Monitor therapy

Antipsychotic Agents (Second Generation [Atypical]): Blood Pressure Lowering Agents may enhance the hypotensive effect of Antipsychotic Agents (Second Generation [Atypical]). Monitor therapy

Barbiturates: May enhance the hypotensive effect of Blood Pressure Lowering Agents. Monitor therapy

Benperidol: May enhance the hypotensive effect of Blood Pressure Lowering Agents. Monitor therapy

Beta-Blockers: May enhance the orthostatic hypotensive effect of Alpha1-Blockers. The risk associated with ophthalmic products is probably less than systemic products. Exceptions: Levobunolol; Metipranolol. Monitor therapy

Brigatinib: May diminish the antihypertensive effect of Antihypertensive Agents. Brigatinib may enhance the bradycardic effect of Antihypertensive Agents. Monitor therapy

Brimonidine (Topical): May enhance the hypotensive effect of Blood Pressure Lowering Agents. Monitor therapy

Calcium Channel Blockers: Alpha1-Blockers may enhance the hypotensive effect of Calcium Channel Blockers. Monitor therapy

Dapoxetine: May enhance the orthostatic hypotensive effect of Alpha1-Blockers. Monitor therapy

Diazoxide: May enhance the hypotensive effect of Blood Pressure Lowering Agents. Monitor therapy

DULoxetine: Blood Pressure Lowering Agents may enhance the hypotensive effect of DULoxetine. Monitor therapy

Herbs (Hypertensive Properties): May diminish the antihypertensive effect of Antihypertensive Agents. Monitor therapy

Herbs (Hypotensive Properties): May enhance the hypotensive effect of Blood Pressure Lowering Agents. Monitor therapy

Hypotension-Associated Agents: Blood Pressure Lowering Agents may enhance the hypotensive effect of Hypotension-Associated Agents. Monitor therapy

Levodopa: Blood Pressure Lowering Agents may enhance the hypotensive effect of Levodopa. Monitor therapy

Lormetazepam: May enhance the hypotensive effect of Blood Pressure Lowering Agents. Monitor therapy

Methylphenidate: May diminish the antihypertensive effect of Antihypertensive Agents. Monitor therapy

Molsidomine: May enhance the hypotensive effect of Blood Pressure Lowering Agents. Monitor therapy

Nicorandil: May enhance the hypotensive effect of Blood Pressure Lowering Agents. Monitor therapy

Nitroprusside: Blood Pressure Lowering Agents may enhance the hypotensive effect of Nitroprusside. Monitor therapy

Obinutuzumab: May enhance the hypotensive effect of Blood Pressure Lowering Agents. Management: Consider temporarily withholding blood pressure lowering medications beginning 12 hours prior to obinutuzumab infusion and continuing until 1 hour after the end of the infusion. Consider therapy modification

Pentoxifylline: May enhance the hypotensive effect of Blood Pressure Lowering Agents. Monitor therapy

Pholcodine: Blood Pressure Lowering Agents may enhance the hypotensive effect of Pholcodine. Monitor therapy

Phosphodiesterase 5 Inhibitors: May enhance the hypotensive effect of Alpha1-Blockers. Management: Ensure patient is stable on one agent prior to initiating the other, and always initiate combination using the lowest possible dose of the drug being added. When tadalafil is used for treatment of BPH, concurrent alpha 1-blockers are not recommended. Consider therapy modification

Prostacyclin Analogues: May enhance the hypotensive effect of Blood Pressure Lowering Agents. Monitor therapy

Quinagolide: May enhance the hypotensive effect of Blood Pressure Lowering Agents. Monitor therapy

Rilmenidine: Alpha1-Blockers may enhance the hypotensive effect of Rilmenidine. Monitor therapy

Yohimbine: May diminish the antihypertensive effect of Antihypertensive Agents. Monitor therapy

Blood levels of prazosin reach a peak within about three hours of an oral dose. The blood pressure lowering effect occurs within two hours of a dose and reaches a peak at two to four hours.

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