Class: Alpha-1 adrenergic blocker
- Capsules 1 mg
- Capsules 2 mg
- Capsules 5 mg
Selectively blocks postsynaptic alpha-1 adrenergic receptors, resulting in dilation of arterioles and veins.
T max is approximately 3 h. Oral bioavailability is 48% to 68%.
Protein binding is 92% to 97%.
Extensively metabolized by demethylation and conjugation in the liver.
Urine (less than 10%); feces (less than 90%). Plasma t ½ is 2 to 3 h.
Duration of antihypertensive effect is 10 h.
Elimination is slower.Chronic renal failure
Elimination half-life prolonged, protein binding decreased, and peak plasma concentrations increased.
Indications and Usage
Treatment of hypertension.
Hypersensitivity to doxazosin, prazosin, or terazosin.
Dosage and AdministrationAdults Initial dose
PO 1 mg twice daily to 3 times daily.Maintenance
PO 6 to 20 mg/day in divided doses (max, 40 mg/day).Children
PO 0.5 to 7 mg 3 times daily has been suggested.
- Give initial dose at bedtime to avoid syncope.
Store at controlled room temperature (59° to 86°F).
Increased risk of hypotension.Beta-blockers
Enhanced acute orthostatic hypotensive reaction after first dose of prazosin.Verapamil
Increased serum prazosin levels and increased sensitivity to orthostatic hypotension.
Laboratory Test Interactions
May cause false elevation in vanillylmandelic acid.
Palpitations; orthostatic hypotension; hypotension; tachycardia.
Depression; dizziness; nervousness; paresthesia; asthenia; drowsiness; headache.
Pruritus; rash; sweating; alopecia; lichen planus.
Blurred vision; conjunctivitis; tinnitus; nasal congestion; epistaxis.
Nausea; vomiting; dry mouth; diarrhea; constipation; abdominal discomfort or pain.
Impotence; urinary frequency; incontinence; priapism.
Arthralgia; edema; fever.
Category C .
Excreted in breast milk.
Safety and efficacy not established.
When adding a diuretic or other antihypertensive agent, reduce dosage to 1 to 2 mg 3 times daily and then retitrate.
May cause marked hypotension (especially orthostatic) and syncope at 30 min after first few doses, after reintroduction, with rapid increase (at least 2 mg) in dosing, or after addition of another antihypertensive. To avoid, initiate dosing with low dose (1 mg or up to 2 mg) and gradually increase after 2 wk.
May decrease total cholesterol levels and LDLs and increase HDLs.
Drowsiness, depressed reflexes, hypotension.
- Advise patient to take medication at same time each day.
- Warn patient about possibility of syncope or orthostasis.
- Instruct patient to report the following symptoms to health care provider: dizziness, palpitations, drowsiness, fatigue, nausea, headache.
- Caution patient to avoid sudden position changes to prevent orthostatic hypotension.
- Advise patient to avoid driving or performing other tasks requiring mental alertness for 12 to 24 h after first dose, after dosage increase, and after resuming treatment after interruption. After the 12- to 24-h period, advise patient to use caution.
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