Description

Hypertension: Prazosin is indicated in the treatment of all grades of essential (primary) hypertension and of all grades of secondary hypertension of variec etiology. It can be used as the initial and sole agent or it may be employed in a treatment program in combination with a diuretic and/or other antihypertensive drugs as needed for proper patient response. Renal blood flow and glomerular filtration rate are not impaired by long-term oral administration and thus Prazosin can be used with safety in hypertensive patients with impaired renal function. Left Ventricular Failure: Prazosin is indicated in the treatment of left ventricular failure. Prazosin may be added to the therapeutic regimen in those patients who have not shown a satisfactory response or who have become refractory to conventional therapy with diuretics, with or without cardiac glycosides. Raynaud's Phenomenon And Raynaud's Disease: Prazosin indicated in the treatment of Raynaud's phenomenon and Raynaud's disease. Benign Prostatic Hyperplasia: Prazosin is indicated as an adjunct in the symptomatic treatment of urinary obstruction caused by benign prostatic hyperplasia. It is also of value in patients awaiting prostatic surgery.

Prazosin is contraindicated in patients with a known sensitivity to quinazolines.

The most common reactions associated with Prazosin therapy are dizziness, headache, drowsiness, lack of energy, weakness, palpitations and nausea. In most instances, side effects have disappeared with continued therapy or have been tolerated with no decrease in the dosage of the drug. In addition, the following reactions have been associated with Prazosin therapy; vomiting diarrhea, constipation, abdominal discomfort and/or pain, 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, reddened solera, epistaxis, tinnitus, dry mouth, nasal congestion, diaphoresis, fever, positive ANA liter, and arthralgia. Some of these reactions have occurred rarely, and in many instances, the exact causal relationships have not been established. Literature reports exist associating Prazosin, therapy with a worsening of pre-existing narcolepsy. A causal relationship is uncertain in these cases. The following have been observed in parents being managed for left ventricular failure with Prazosin when used in conjunction with cardiac glycosides and diuretics; drowsiness, dizziness, postural hypotension, blurred vision, edema, dry mouth, palpitations, nausea, diarrhea, impotence, headache, and nasal congestion. In most instances, these occurrences have been mild to moderate in severity and have resolved with continued therapy or have been tolerated with no decrease in drug dosage. The most commonly although infrequently reported side effect in the treatment of Raynaud's Phenomenon/Disease was mild dizziness.

Although no teratogenic effects were seen in animal testing; the safety of Prazosin use during. pregnancy has not yet been established. The use of prazosin and a beta-blocker for the control of sever hypertension of 44 pregnant women revealed no drug-related fetal adnormalities or adverse effects. Therapy with prazosin was continued for as long as 14 weeks. Prazosin has also been used alone or in combination with other hypotensive agents in severe hypertension or pregnancy. No fetal or neonatal abnormalities have been reported with the use of Prazosin. There are no adequate and well controlled studies that establish the safety of Prazosin in pregnant women. Prazosin should be used during pregnancy only if in the opinion of the physician the potential benefit justifies the potential risk to the mother and fetus. Prazosin has been shown to be excreted in small amounts in human milk. Caution shold be exercised when Prazosin is adminsitered to nursing mothers.

Hypertension: A very small percentage of patients have responded in an abrupt and exaggerated manner to the initial dose of Prazosin. Postural hypotension evidenced by dizziness and weakness, or rarely loss of consciousness, has been reported, particularly with the commencement of therapy, but this effect is readily avoided by initiating treatment with a low dose of Prazosin XR and with small increases in dosage during the first one to two weeks of therapy. The effect when observed is not related to the severity of hypertension is self-limiting and in most patients does not recur after the initial period of therapy or during subsequent dose titration steps. When instituting therapy with any effective antihypertensive agent, the patient should be advised how to avoid symptoms resulting from postural hypotension and what measures to take should they develop. The patient should be cautioned to avoid situations where injury could result should dizziness or weakness occur during the initiation of Prazosin therapy. Left Ventricular Failure: When prazosin is initially administered to patients with left ventricular failure who have undergone vigorous diuretic or other vasodilator treatment, particularly in higher than the recommended starting dose, the resultant decrease in left ventricular filling pressure may be associated with a significant fall in cardiac output and systemic blood pressure. In such patients, observance of the recommended starting dose of prazosin followed by gradual titration is particularly important. (See dosage and administration). In occasional patients with left ventricular failure, the clinical efficacy of Prazosin has been reported to diminish after several months of treatment. In these patients, there is usually evidence of weight gain or peripheral edema indicating fluid retention. Since spontaneous deterioration may occur in such severely ill patients a causal relationship to prazosin therapy has not been established. Thus, as with all patients with left ventricular failure, careful adjustment of diuretic dosage according to the patient's clinical condition is required to prevent excessive fluid retention and consequent relief of symptoms. In those patients without evidence of fluid retention, when clinical improvement has diminished; an increase in the dosage, of Prazosin will usually restore clinical efficacy. Raynaud's Phenomenon and Raynaud's Disease: Because Prazosin decreases peripheral vascular resistance, careful monitoring of blood pressure during initial administration and titration of Prazosin is suggested. Close observation is especially recommended for patients already taking medication that are known the lower blood pressure. Benign Prostatic Hyperplasia: Prazosin decreases peripheral vasular resistance and since many patients with this disorder are elderly, careful monitoring of blood pressure during initial administration and during adjustment of the dose of Prazosin is suggested. Close observation is especially recommended for patients taking medications that are known to lower blood pressure.

Children: Prazosin is not recommended for the treatment of children under the age of 12 years since safe conditions for its use have not been established. Left Ventricular Failure: Prazosin is not recommended in the treatment of left ventricular failure due to mechanical obstrcution such as aortic valve stenosis, mitral valve stenosis, pulmonary embolism and restrictive pericardial disease. Adequate data are not yet available to establish efficacy in patients with left ventricular failure due to a recent myocardial infarction.

Accidental ingestion of at least 50 mg of Prazosin in a two-year child resulted in profound drowsiness and depressed reflexes, No decrease in blood pressure was noted. Recovery was uneventful. Should overdosage lead to hypotension, support of the cardiovascular system is of first importance. Restoration of blood pressure and normalization of heart rate may be accomplished by keeping the patient in the supine position. If this measure is inadequate, shock should first be treated with volume expanders. If necessary, vasopressors should then be used. Renal function should be monitored and supported as needed. Laboratory data indicate Prazosin is not dialyzable because it is protein bound.