The therapeutic efficacy of Prazosin in patients with congestive heart failure is ascribed to a reduction in left ventricular filling pressure, reduction in cardiac impedance and an augmentation of cardiac output. The use of Prazosin in congestive heart failure does not provoke a reflex tachycardia and blood pressure reduction is minimal in normotensive patients. Prazosin reduce the severity of the signs, symptoms, frequency and duration of attacks, in patients with Raynaud’s disease. In low dosage, antagonism of alpha-1-receptors on prostatic and urethral smooth muscle has been shown to improve the urinary pressure profile in men and to improve symptoms of benign prostatic hyperplasia. Clinical studies have shown that Prazosin therapy is not associated with adverse changes in the serum lipid profile.
- Recommended starting dose is 0.5 mg (in the evening), twice or thrice daily for 3 to 7 days. This dose should be increased to 1 mg twice or three times daily for a further 3 to 7 days. Thereafter, the daily dose should be increased gradually as determined by the patient’s response to the blood pressure lowering effect. Most patients are likely to be maintained on a dosage regimen of Prazosin alone of up to 15 mg daily in divided doses.
- Maximum dose: 20 mg in divided doses.
Patients receiving other antihypertensive therapy but with inadequate control:
- The dosage of the other drug should be reduced to a maintenance level and Prazosin initiated at 0.5 mg in the evening, then continuing with 0.5 mg twice or three times daily.
- Subsequent dosage increases should be made gradually depending upon the patient’s response.
Congestive heart failure:
- The recommended starting dose is 0.5 mg two, three or four times daily, increasing to 4 mg in divided doses. Dosage should be adjusted according to the patient’s response, based on careful monitoring of cardiopulmonary signs and symptoms.
- Usual daily maintenance dosage: 4 mg to 20 mg in divided doses.
- The recommended starting dosage is 0.5 mg twice daily given for a period of 3 to 7 days and should be adjusted according to the patient’s clinical response.
- Usual maintenance dosage is 1 mg or 2 mg twice daily.
Benign prostatic hyperplasia:
- The recommended dosage is 0.5 mg twice daily for a period of 3 to 7 days, with the initial dose administered in the evening. The dosage should then be adjusted according to clinical response.
- The usual maintenance dosage is 2 mg twice daily.
Pregnancy & Lactation
In patients with congestive heart failure: Prazosin is not recommended in the treatment of congestive cardiac failure due to mechanical obstruction such as aortic valve stenosis, mitral valve stenosis, pulmonary embolism and restrictive pericardial disease.
In patients with hypertension: Postural hypotension evidenced by dizziness and weakness, or rarely loss of consciousness, has been reported, particularly with the commencement of therapy
Management: Symptomatic and supportive treatment. May be treated with activated charcoal if patient presents within 1 hr of ingestion. Postural measures and parenteral fluid volume replacement for severe hypotension and if necessary, cautious IV infusion of a vasopressor.
Use in Special Population
Patients with hepatic dysfunction: it is recommended that therapy should be initiated at 0.5 mg daily and that dosage should be increased cautiously.
Use in the elderly: Since the elderly may be more susceptible to hypotension, therapy should be initiated with the lowest possible dose.