Prazosin Hydrochloride

Prazosin Hydrochloride

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Questions & Answers

Side Effects & Adverse Reactions

As with all alpha-blockers, prazosin hydrochloride 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 to 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. 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 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 prazosin hydrochloride capsules, 1 mg. 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.

Legal Issues

There is currently no legal information available for this drug.

FDA Safety Alerts

There are currently no FDA safety alerts available for this drug.

Manufacturer Warnings

There is currently no manufacturer warning information available for this drug.

FDA Labeling Changes

There are currently no FDA labeling changes available for this drug.


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


There is currently no drug history available for this drug.

Other Information

Prazosin hydrochloride, a quinazoline derivative, is the first of a new chemical class of antihypertensives. It is the hydrochloride salt of 1-(4-amino-6,7-dimethoxy-2-quinazolinyl)-4-(2-furoyl) piperazine and its structural formula is:

prazosin hydrochloride capsules structural formula

C19H21N5O4•HCl          M.W. 419.87

It is a white, crystalline substance, slightly soluble in water and isotonic saline.

Each capsule for oral administration, contains prazosin hydrochloride, USP equivalent to 1 mg, 2 mg or 5 mg of prazosin. Inactive ingredients include: anhydrous lactose, magnesium stearate, and pregelatinized starch. Additional inactive ingredients for the gelatin capsule include: 1 mg (Ivory): D&C Yellow No. 10 and titanium dioxide; 2 mg (Pink): FD&C Blue No. 1, FD&C Red No. 40, D&C Red No. 28, and titanium dioxide; 5 mg (Light Blue): FD&C Blue No. 1 and titanium dioxide.

Prazosin Hydrochloride Manufacturers

  • American Health Packaging
    Prazosin Hydrochloride Capsule [American Health Packaging]
  • State Of Florida Doh Central Pharmacy
    Prazosin Hydrochloride Capsule [State Of Florida Doh Central Pharmacy]
  • Pd-rx Pharmaceuticals, Inc.
    Prazosin Hydrochloride (Prazosin Hydrochloride) Capsule [Pd-rx Pharmaceuticals, Inc.]
  • Pd-rx Pharmaceuticals, Inc.
    Prazosin Hydrochloride (Prazosin Hydrochloride) Capsule [Pd-rx Pharmaceuticals, Inc.]
  • Udl Laboratories, Inc.
    Prazosin Hydrochloride Capsule [Udl Laboratories, Inc.]
  • Remedyrepack Inc.
    Prazosin Hydrochloride Capsule [Remedyrepack Inc. ]
  • Remedyrepack Inc.
    Prazosin Hydrochloride (Prazosin Hydrochloride) Capsule [Remedyrepack Inc. ]
  • Remedyrepack Inc.
    Prazosin Hydrochloride Capsule [Remedyrepack Inc. ]
  • Aphena Pharma Solutions – Tennessee, Inc.
    Prazosin Hydrochloride Capsule [Aphena Pharma Solutions – Tennessee, Inc.]
  • Physicians Total Care, Inc.
    Prazosin Hydrochloride Capsule [Physicians Total Care, Inc.]
  • Remedyrepack Inc.
    Prazosin Hydrochloride Capsule [Remedyrepack Inc. ]
  • Remedyrepack Inc.
    Prazosin Hydrochloride Capsule [Remedyrepack Inc. ]
  • Teva Pharmaceuticals Usa Inc
    Prazosin Hydrochloride Capsule [Teva Pharmaceuticals Usa Inc]
  • Aidarex Pharmaceuticals Llc
    Prazosin Hydrochloride Capsule [Aidarex Pharmaceuticals Llc]
  • Aphena Pharma Solutions – Tennessee, Llc
    Prazosin Hydrochloride Capsule [Aphena Pharma Solutions – Tennessee, Llc]
  • Carilion Materials Management
    Prazosin Hydrochloride Capsule [Carilion Materials Management]
  • Mylan Pharmaceuticals Inc.
    Prazosin Hydrochloride Capsule [Mylan Pharmaceuticals Inc.]
  • Bryant Ranch Prepack
    Prazosin Hydrochloride Capsule [Bryant Ranch Prepack]

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