Prazosin: Description, Side Effects, Indications, Dosage and Administration

Also known by commercial names such as Hypovase, Minipress, Vasoflex, and Press, it is a sympatholytic drug used primarily to treat hypertension.


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

  • Prazosina hydrochloride.
  • Fórmula molecular C19H21N5O4 • HCl.

It is a white, crystalline substance, slightly soluble in water and isotonic saline, and its molecular weight is 419.87.

Each 1 mg capsule for oral use contains a drug equivalent to 1 mg of the free base.

The inert ingredients in the formulations are hard gelatin capsules (which may contain blue 1, red 3, red 28, red 40, and other inactive ingredients), magnesium stearate, sodium lauryl sulfate, starch, and sucrose.

What are the possible side effects of Prazosin?

Seek emergency medical attention if you have any of these symptoms of an allergic reaction such as hives, difficult breathing, or swelling of your face, lips, tongue, or throat.

Call your doctor right away if you have a severe side effect, such as:


  • Fast or strong heartbeat or fluttering in your chest.
  • Feeling that you can faint.
  • Difficulty breathing.
  • Swelling in your hands, ankles, or feet.
  • Erection of the penis that is painful or lasts 4 hours or more.

Less serious side effects may include:

  • Slight dizziness
  • Weakness, tiredness


It is indicated for the treatment of hypertension to reduce blood pressure.

The decrease in blood pressure reduces the risk of fatal and non-fatal cardiovascular events, mainly strokes and myocardial infarcts.

These benefits have been observed in controlled trials of antihypertensive drugs from various pharmacological classes, including this drug.

The control of high blood pressure should be part of the integral management of cardiovascular risk.

This includes, as appropriate, lipid control, diabetes control, antithrombotic therapy, smoking cessation, exercise, and limited sodium intake.

Many patients will need more than one medication to achieve blood pressure goals.

For specific advice on objectives and management, see published guidelines.

Like those of the Joint National Committee for the Prevention of Arterial Hypertension on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC).

Numerous antihypertensive drugs, from various pharmacological classes and with different mechanisms of action, have been demonstrated in randomized controlled trials to reduce cardiovascular morbidity and mortality.

It can be concluded that it is the reduction of blood pressure and not other pharmacological properties of the drugs primarily responsible for those benefits.

The most significant and most consistent cardiovascular benefit has been a reduction in the risk of stroke, but reductions in myocardial infarction and cardiovascular mortality have also been seen regularly.

High systolic or diastolic pressure causes an increase in cardiovascular risk, and the absolute increase in risk per mmHg is more significant at higher blood pressures.

So even moderate reductions in severe hypertension can provide a substantial benefit.

The reduction of the relative risk of blood pressure reduction is similar in populations with variable absolute risk, so the total benefit is higher in patients with higher risk regardless of their hypertension.

For example, patients with diabetes or hyperlipidemia, and such patients would be expected to benefit from a more aggressive treatment at a lower blood pressure target.

Some antihypertensive drugs have more minor blood pressure effects (such as monotherapy).

Many antihypertensive drugs have approved indications and additional effects (such as angina, heart failure, or diabetic kidney disease).

These considerations can guide the selection of therapy.

Prazosin can be used alone or combined with other antihypertensive drugs, such as diuretics or beta-adrenergic blockers.

Dosage and administration

The dose of Prazosin should be adjusted according to the patient’s blood pressure response. The following is a guide for your administration:

Initial dose

  • 1 mg two or three times a day.

Maintenance dose

  • The dosage can be increased slowly to a total daily dose of 20 mg administered in divided doses.
  • The most commonly used therapeutic dosages have varied from 6 mg to 15 mg daily in divided doses.
  • Doses above 20 mg generally do not increase efficacy. However, some patients may benefit from additional increases up to a daily dose of 40 mg administered in divided doses.
  • After the initial titration, some patients can be adequately maintained on a dosing regimen twice a day.

Use with other drugs.

When a diuretic or other antihypertensive agent is added, the dose of Prazosin should be reduced to 1 mg or 2 mg three times a day, and the re-titration is carried out.