Hypertension: G-Prazosin is indicated for the treatment of all grades of essential (primary) hypertension and secondary hypertension of various etiologies. It may be used as initial monotherapy or in combination with a diuretic and/or other antihypertensive agents, depending on patient response. Long-term oral use does not impair renal blood flow or glomerular filtration rate; therefore, it can be safely used in hypertensive patients with renal impairment.

Left Ventricular Failure: G-Prazosin is indicated in the management of left ventricular failure. It may be added to treatment in patients who have an inadequate response or have become refractory to conventional therapy with diuretics, with or without cardiac glycosides.

Raynaud’s Phenomenon and Raynaud’s Disease: G-Prazosin is indicated for the treatment of Raynaud’s phenomenon and Raynaud’s disease.

Benign Prostatic Hyperplasia (BPH): G-Prazosin is used as an adjunct in the symptomatic treatment of urinary obstruction due to benign prostatic hyperplasia. It is also useful in patients awaiting prostate surgery.

Prazosin produces a reduction in total peripheral vascular resistance through selective blockade of postsynaptic alpha-1 adrenergic receptors in vascular smooth muscle. In hypertensive patients, it lowers blood pressure in both supine and standing positions, with a more pronounced effect on diastolic pressure. Abrupt discontinuation does not cause rebound hypertension.

In congestive heart failure, its beneficial effects are due to reduced left ventricular filling pressure, decreased cardiac impedance, and increased cardiac output. It does not cause reflex tachycardia, and blood pressure reduction in normotensive patients is minimal. In Raynaud’s disease, prazosin reduces the severity, frequency, and duration of attacks. In low doses, alpha-1 receptor blockade in prostatic and urethral smooth muscle improves urinary flow and relieves symptoms of BPH. Clinical studies show that prazosin does not adversely affect serum lipid profiles.

Prazosin Tablet: There is evidence that toleration is best when therapy is initiated with a low starting dose. During the first week, the dosage of Prazosin should be adjusted according to the patient's individual toleration. Thereafter the daily dosage is to be adjusted on the basis of the patient's response. The response is usually seen within one to 14 days if it is to occur at any particular dose. When a response is seen, therapy should be continued at that dosage until the degree of response has reached optimum before the next dose increment is added.

• Hypertension: For maximum benefit, small increases should be continued until the desired effect is achieved or a total daily dosage of 20 mg is reached. A diuretic or adrenergic beta-blocking agent may be added to enhance efficacy. The maintenance dosage of Prazosin may be given as a twice or three times daily regimen.
• Patients Receiving No Antihypertensive Therapy: It is recommended that therapy be initiated with 0.5 mg given in the evening at bedtime then 0.5 mg b.i.d. or t.i.d for three to seven days. Unless poor toleration suggests the patient is unusually sensitive, this dosage should be increased to 1 mg given b.i.d. or t.i.d. for a further three to seven days. Thereafter, as determined by the patient's response to the blood pressure lowering effect, the dosage should be increased gradually to a total daily dosage of 20 mg given in divided doses.
• Patients Receiving Diuretic Therapy With inadequate Control of Blood Pressure: The diuretic should be reduced to a maintenance dosage level for the particular agent and Prazosin initiated with 0.5 mg h.s then proceeding to 0.5 mg b.i.d or t.i.d. After the initial period of observation, the dosage of Prazosin should be gradually increased as determined by the patient's response.
• Patients Receiving Other Antihypertensives But With Inadequate Control: Because some additive effect is anticipated, the other agent dosage level (e.g. beta-adrenergic blocking agents, methyldopa, reserpine, lslnidine etc.) should be reduced and Prazosin initiated at 0.5 mg h.s. then proceeding to 0.5 mg b.i.d, or t.i.d. Subsequent dosage increase should be made depending upon the patient's response. There is evidence that adding Prazosin to beta-adrenergic blocking agents, calcium antagonists or ACE inhibitors may bring about a substantial reduction in blood pressure. Thus, a low initial dosage regimen is strongly recommended.
• Patients With Moderate to Severe Grades of Renal Impairment: Evidence to date shows that Prazosin does not further compromise renal function when used in patients with renal impairment. Because some patients in this category have responded to small doses of Prazosin, it is recommended that therapy be initiated at 0.5 mg daily and that dosage increases be instituted cautiously.

Left Ventricular Failure: The recommended starting dose is 0.5 mg two, three or four times a day. Dosage should be titrated according to the patient's clinical response, based on careful monitoring of cardiopulmonary signs and symptoms, and when indicated, hemodynamic studies. Dosage titration steps may be performed as often as every two or three days in patients under close medical supervision. In severely ill, decompensated patients, rapid dosage titration over one to two days may be indicated and is best done when hemodynamic monitoring is available. In clinical studies, the therapeutic dosages ranged from 4 mg to 20 mg daily in divided doses. Adjustment of dosage may be required in the course of Prazosin therapy in some patients to maintain optimal clinical improvement.
Suggested Starting Dosage: 0.5 mg b.i.d., t.i.d. or q.i.d increasing to 4 mg in divided doses.
Use Daily Maintenance Dosage: 4 mg once daily to 20 mg in divided doses.

Raynaud's Phenomenon And Raynaud's Disease: The recommended starting dosage is 0.5 mg b.i.d. given for a period of three to seven days. Dosage should be adjusted according to the patient's clinical response.
Suggested Starting Dosage: 0.5 mg b.i.d.
Usual Daily Maintenance Dosage: 1 mg or 2 mg b.i.d. Doses up to 2 mg t.i.d. may be required for some patients.

Benign Prostatic Hyperplasia: The recommended starting dose is 0.5 mg twice daily given for a period of 3 to 7 days and should then be adjusted according to the patient's clinical responses. The usual maintenance dose is 2 mg twice daily. The safety and efficacy of a total daily dosage greater than 4 mg have not been established. Therefore, total daily dosages greater than 4 mg should be used with caution.

Prazosin XR Tablet: Prazosin XR Extended-Release Tablets must be swallowed whole and should not be bitten or divided. Therapy for hypertension with Prazosin XR must be initiated at 2.5 mg once daily. The 5 mg dosage form of Prazosin XR is not for initial dosing. Dosage may be increased slowly, in general over a 7 to 14-day period, depending on the response to each dose level. Doses above 20 mg once daily have not been studied.

Maintenance Dose: Dosage may be increased as clinically indicated to 20 mg given in once-daily doses.

Hypertensive patients controlled on Prazosin Tablets alone or in combination with other antihypertensive medications may be switched to Prazosin XR Extended Release Tablets at the equivalent or nearest higher total daily dose, e.g. Prazosin Tablets 4 mg daily equivalent to Prazosin XR Extended Release Tablets 5 mg once daily. Blood pressure measurements should be taken at the end of the dosing interval to assure adequate blood pressure control is maintained throughout the 24-hour period. Further titration may be necessary in some patients.

The addition of a diuretic or other antihypertensive agent to prazosin has been shown to cause an additive hypotensive effect.

Prazosin is contraindicated in patients with known hypersensitivity to quinazoline derivatives.

The most commonly reported adverse effects include dizziness, headache, drowsiness, fatigue, weakness, palpitations, and nausea. These symptoms often resolve with continued therapy or are tolerated without dose reduction. Other reported effects include vomiting, diarrhea, constipation, abdominal pain or discomfort, liver function abnormalities, pancreatitis, edema, orthostatic hypotension, dyspnea, faintness, tachycardia, nervousness, vertigo, hallucinations, depression, paresthesia, rash, pruritus, alopecia, lichen planus, urinary frequency, impotence, incontinence, priapism, blurred vision, conjunctival redness, epistaxis, tinnitus, dry mouth, nasal congestion, sweating, fever, positive ANA titer, and arthralgia. Some reactions are rare and causal relationships are not always confirmed. Reports have also suggested possible worsening of pre-existing narcolepsy, though causality is uncertain. In patients with left ventricular failure treated with prazosin along with cardiac glycosides and diuretics, reported effects include drowsiness, dizziness, postural hypotension, blurred vision, edema, dry mouth, palpitations, nausea, diarrhea, impotence, headache, and nasal congestion. These are generally mild to moderate and often resolve with continued therapy. In Raynaud’s phenomenon/disease, the most commonly reported side effect is mild dizziness.

Animal studies have shown no teratogenic effects; however, the safety of prazosin during human pregnancy has not been fully established. Limited clinical data, including use in severe hypertension during pregnancy (alone or with beta-blockers), have not shown fetal abnormalities or adverse outcomes. No adequate and well-controlled studies exist in pregnant women. Therefore, prazosin should be used during pregnancy only if the potential benefit justifies the potential risk to the mother and fetus. Small amounts of prazosin are excreted in human breast milk. Caution is advised when administering to breastfeeding mothers.

Hypertension: A small percentage of patients may experience an abrupt and exaggerated response to the initial dose of prazosin. Postural hypotension, manifested by dizziness, weakness, or rarely loss of consciousness, may occur, particularly at the start of therapy. This can usually be avoided by initiating treatment with a low dose of Prazosin XR and gradual dose increases over the first 1–2 weeks.

This effect is not related to the severity of hypertension, is self-limiting, and usually does not recur after the initial treatment period or during later dose adjustments. Patients should be informed about symptoms of postural hypotension and advised on how to manage them. They should also be cautioned to avoid situations where dizziness or weakness could lead to injury during therapy initiation.

Left Ventricular Failure: In patients with left ventricular failure who have previously received intensive diuretic or vasodilator therapy, particularly at higher than recommended starting doses, prazosin may cause a marked reduction in left ventricular filling pressure, leading to decreased cardiac output and systemic blood pressure. Therefore, starting with a low dose followed by gradual titration is essential.

In some patients, the clinical effect of prazosin may diminish after several months, often associated with weight gain or peripheral edema indicating fluid retention. A direct causal relationship has not been established. Diuretic therapy should be carefully adjusted to prevent fluid overload. In patients without fluid retention, increasing the dose may restore therapeutic response.

Raynaud’s Phenomenon and Raynaud’s Disease: Since prazosin reduces peripheral vascular resistance, blood pressure should be carefully monitored during initiation and dose titration. Extra caution is needed in patients already receiving antihypertensive medications.

Benign Prostatic Hyperplasia (BPH): As prazosin lowers peripheral vascular resistance and many BPH patients are elderly, careful blood pressure monitoring is required during initiation and dose adjustment. Caution is advised in patients taking other blood pressure–lowering medications.

Children: Prazosin is not recommended for children under 12 years of age, as safety has not been established.

Left Ventricular Failure: Prazosin is not recommended in left ventricular failure due to mechanical obstruction such as aortic or mitral valve stenosis, pulmonary embolism, or restrictive pericardial disease. Its efficacy in heart failure following recent myocardial infarction has not been established.

Accidental ingestion of at least 50 mg in a 2-year-old child resulted in profound drowsiness and reduced reflexes without significant hypotension, and recovery was uneventful. In case of overdose with hypotension, cardiovascular support is the primary management. Blood pressure and heart rate may be stabilized by placing the patient in a supine position. If inadequate, volume expanders should be used, followed by vasopressors if necessary. Renal function should be monitored and supported. Prazosin is not dialyzable due to high protein binding.

Alpha-adrenoceptor blocking drugs

Store below 30°C, protected from light and moisture. Keep out of reach of children.