prazosin (Minipress)

Prazosin (Minipress) is an oral medicine used to treat high blood pressure. Prazosin is a competitive alpha-1 adrenergic receptor blocker. By blocking alpha-1 receptors on muscle cesll that surround blood vessels, prazosin causes vasodilation (widening) of the blood vessels, and consequently decreases the resistance of blood flow. The overall benefit of its use is a decrease in blood pressure.

Prazosin seems to have a bigger impact on reducing the diastolic blood pressure than systolic blood pressure. Diastolic blood pressure is indicated by the second set of numbers in the blood pressure reading and corresponds to the minimum pressure in the arteries when the heart muscles are relaxed and the chambers of the heart are filling with blood.

Prazosin was approved by the FDA in 1976.

Minipress

GENERIC AVAILABLE: Yes

Yes

The most common side effects associated with prazosin treatment include:

• dizziness,
• headache,
• drowsiness,
• lack of energy,
• weakness,
• palpitations, and
• nausea.

Patients can lower their chance of feeling dizzy or passing out by:

• rising slowing from a sitting or lying position,
• climbing stairs slowly,
• avoiding alcohol, and
• drinking lots of water especially in hot weather or while being active.

 Additionally, patients should have their blood pressure checked regularly.

Less common side effects include:

• vomiting,
• diarrhea,
• constipation,
• water retention (edema),
• orthostatic hypotension,
• shortness of breath,
• fainting (syncope),
• motion sickness,
• depression,
• nervousness,
• rash,
• urinary frequency,
• blurred vision,
• reddened sclera,
• nosebleeds,
• dry mouth, and nasal
• congestion.

Rare side effects include:

• stomach pain,
• liver problems,
• pancreatitis,
• tachycardia (fast heartbeat),
• paresthesia (numbness, tingling, burning, prickling),
• hallucinations,
• itching,
• hair loss,
• urinary incontinence (loss of bladder control),
• sexual dysfunction,
• prolonged erection,
• ringing in the ears,
• sweating,
• fever, and
• joint pain.

Other side effects reported in post-marketing trials include:

• allergic reaction,
• weakness,
• pain,
• chest pain,
• low blood pressure,
• gynecomastia (enlargement of mens' breasts, bradycardia [slow heartbeat]),
• difficulty sleeping,
• hives,
• vasculitis, and
• eye pain. 

• The dose of prazosin should be adjusted based on the individual patient response.
• For the treatment of high blood pressure: Most patients are started with 1 mg by mouth 2-3 times a day. To decrease the risk of orthostatic hypotension the first dose may be given at bedtime. Orthostatic hypotension is a drop in blood pressure when standing up from a sitting or lying position. Dosage may be increased gradually over time to a total daily dose of 20 mg given in multiple doses.
• If adding another blood pressure lowering agent or water pill (diuretic) to prazosin therapy, the dose of prazosin should be reduced to 1-2 mg by mouth three times a day, followed by slow increases in dose as needed.
• As elderly patients are more sensitive to the side effects of low blood pressure, dose reduction in the elderly is necessary. Most elderly patients are started on 1 mg by mouth 1-2 times daily.
• The safety and effectiveness of prazosin in children has not been established.

Use of prazosin with other blood pressure lowering medicines or water pills may cause an additive blood pressure lowering effect.

Use of phosphodiesterase-5 (PDE-5) inhibitors, for example, sildenafil (Viagra), tadalafil (Cialis), vardenafil (Levitra) with prazosin can also cause an additive decrease in blood pressure. To decrease the risk of precipitating side effects associated with low blood pressure, the lowest possible dose of PDE-5 inhibitors should be used in patients taking prazosin.

There are no adequate and well controlled studies of prazosin use in pregnancy. Prazosin should be used during pregnancy only if the potential benefit justifies the potential risk to the mother and the unborn baby. Prazosin is classified as FDA pregnancy risk category C (adverse effects in animals but inadequate data in humans).

Small amounts of prazosin were found in human milk after oral administration. Due to the lack of conclusive safety data, prazosin should be used cautiously in nursing mothers.

What preparations of prazosin-oral are available?

Oral capsules: 1, 2, and 5 mg.

How should I keep prazosin-oral stored?

Capsules should be stored at room temperature, between 59 F and 86 F (15 C and 30 C).