Classifications: alpha-adrenergic antagonist; antihypertensive;
Therapeutic: antihypertensive; vasodilator

Prototype: Prazosin
Pregnancy Category: C


1 mg, 2 mg, 5 mg, 10 mg capsules


Quinazoline antihypertensive and vasodilator. Selectively blocks alpha1-adrenergic receptors in vascular smooth muscle, producing relaxation that leads to reduction of peripheral vascular resistance and lowered BP. Vasodilation is accompanied by minimal reflex increase in heart rate.

Therapeutic Effect

Effectiveness is measured in lowering of blood pressure values and controlling the symptoms of benign prostate hypertrophy.


To treat hypertension alone or in combination with other antihypertensive agents (beta-adrenergic blocking agents, diuretics). To treat benign prostatic hypertrophy (BPH) and urinary flow obstruction.


Hypersensitivity to terazosin; pregnancy (category C). Safe use in children is not established.

Cautious Use

Patients with BPH; prostate cancer; history of hypotensive episodes; angina; renal impairment, renal disease, renal failure; elderly; lactation.

Route & Dosage

Hypertension, Benign Prostatic Hypertrophy
Adult: PO Start with 1 mg h.s., then 1–5 mg/d (max: 20 mg/d)


  • Give initial dose at bedtime to reduce the potential for severe hypotensive effect, which may occur with first few doses. After the initial dose, give any time of day.
  • Store at 15°–30° C (59°–86° F) in tightly closed container away from heat and strong light. Do not freeze.

Adverse Effects (≥1%)

CNS: Asthenia (weakness), dizziness, headache, drowsiness, weakness. CV: Postural hypotension, palpitation, first-dose phenomenon (syncope). Special Senses: Blurred vision. GI: Nausea. Body as a Whole: Weight gain, pain in extremities, peripheral edema. Respiratory: Nasal congestion, sinusitis, dyspnea. Urogenital: Impotence.


Drug: Antihypertensive effects may be attenuated by nsaids. Sildenafil, vardenafil, and tadalafil may enhance hypotensive effects.


Absorption: Readily from GI tract. Peak: 1–2 h. Metabolism: In liver. Elimination: 60% in feces, 40% in urine. Half-Life: 9–12 h.

Nursing Implications

Assessment & Drug Effects

  • Be alert for possible first-dose phenomenon (precipitous decline in BP with consciousness disturbance). This is rare; occurs within 90–120 min of initial dose.
  • Monitor BP at end of dosing interval (just before next dose) to determine level of antihypertensive control. Check BP also 2–3 h after the dose to determine if maximum and minimal responses are similar.
  • Be aware that drug-induced decrease in BP appears to be more position dependent (i.e., greater in the erect position) during the first few hours after dosing than at end of 24 h.
  • A greatly diminished hypotensive response at end of 24 h indicates need for change in dosage (increased dose or twice daily regimen). Report to physician.

Patient & Family Education

  • Avoid situations that would result in injury should syncope (loss of consciousness) occur after first dose. If faintness develops, lie down promptly.
  • Make position changes slowly (i.e., change in direction or from recumbent to upright posture). Dangle legs and move ankles a minute or so before standing when arising. Orthostatic hypotension (greatest shortly after dosing) can pose a problem with ambulation.
  • Do not drive or engage in potentially hazardous activities for at least 12 h after first dose, after dosage increase, or when treatment is resumed after interruption of therapy. Twelve hours should be sufficient time for serious adverse effects (syncope, orthostatic hypotension, light-headedness, dizziness) to appear if they are going to do so.
  • Monitor weight: Report sudden gain of more than 0.5–1 kg (1–2 lb) accompanied by edema in extremities to physician. Dose adjustment may be indicated.
  • Do not alter established drug regimen. Consult physician if drug is omitted for several days. Drug will be started with the initial dosing regimen.
  • Keep scheduled appointments for assessment of BP control and other clinically significant tests.
  • Keep a daily record noting BP and time taken, which arm was used, position (i.e., standing, sitting), and time when medication was taken. Take this record to physician for reference at checkup appointment.
  • Do not take OTC medications, particularly those that may contain an adrenergic agent (e.g., remedies for coughs, colds, allergy) without first consulting physician.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

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