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prazosin (pra-zoe-sin)



Therapeutic: antihypertensives

Pharmacologic: peripherally acting antiadrenergics


Mild-to-moderate hypertension. Unlabeled Use: Management of urinary outflow obstruction in patients with benign prostatic hyperplasia.


Dilates both arteries and veins by blocking postsynaptic alpha1-adrenergic receptors. ↓ contractions in smooth muscle of prostatic capsule. Therapeutic Effects: Lowering of blood pressure. ↓ cardiac preload and afterload. ↓ symptoms of prostatic hyperplasia (urinary urgency, urinary hesitancy, nocturia).

Adverse Reactions/Side Effects

CNS: dizziness, headache, weakness, drowsiness, mental depression, syncope. EENT: blurred vision. CV: 1st-dose orthostatic hypotension, palpitations, angina, edema. GI: abdominal cramps, diarrhea, dry mouth, nausea, vomiting. GU: erectile dysfunction, priapism.


Examination and Evaluation

  • Assess blood pressure (BP) periodically and compare to normal values (See Appendix F). Document whether drug therapy is successful in controlling hypertension. Also, be alert for a fall in BP and related symptoms (dizziness, syncope) that occurs when the patient changes position (orthostatic hypotension), especially after the initial dose. Document orthostatic hypotension and contact physician when systolic BP falls >20 mm Hg or diastolic BP falls >10 mm Hg.

  • If treating benign prostate hypertrophy (BPH), monitor signs such as difficulty starting a urine stream, painful urination, weak urine flow, feeling that the bladder is not completely empty, frequent nighttime urination, and an urge to urinate again soon after urinating. Document any change in BPH symptoms to help determine the effects of drug therapy.

  • Assess heart rate, ECG, and heart sounds, especially during exercise (See Appendices G, H). Report any rhythm disturbances or symptoms of increased arrhythmias, including palpitations, chest pain, shortness of breath, fainting, and fatigue/weakness.

  • Assess dizziness and weakness that might affect gait, balance, and other functional activities (See Appendix C). Report balance problems and functional limitations to the physician, and caution the patient and family/caregivers to guard against falls and trauma.

  • Be alert for signs of mental depression or other changes in mood and behavior. Notify physician if these changes become problematic.

  • Assess peripheral edema using girth measurements, volume displacement, and measurement of pitting edema (See Appendix N). Report increased swelling in feet and ankles or a sudden increase in body weight due to fluid retention.


  • Because of the risk of palpitations and abnormal BP responses, use caution during aerobic exercise and other forms of therapeutic exercise. Assess exercise tolerance frequently (BP, heart rate, fatigue levels), and terminate exercise immediately if any untoward responses occur (See Appendix L).

  • Avoid physical therapy interventions that cause systemic vasodilation (large whirlpool, Hubbard tank). Additive effects of this drug and the intervention may cause a dangerous fall in BP.

  • To minimize orthostatic hypotension, advise patient to move ...

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