Prazosin
Antihypertensive · Selective alpha-1 blocker
Indications
Hypertension. Benign prostatic hyperplasia.
Dosage
Hypertension: Adults: 0.5 mg on first evening, then 0.5 mg two or three times daily for 3-7 days, followed by 1 mg two or three times daily for 3-7 days. Thereafter, increase gradually as required. Max: 20 mg daily. Children: Under 12 yr, not recommended. 12-18 yr, 500 mcg 2-3 times daily (initial dose at bedtime), increased after 3-7 days to 1mg 2-3 times daily for a further 3-7 days; further increased gradually if necessary to max 20 mg daily in divided doses. Benign prostatic hyperplasia: Adults: Initially 0.5 mg twice daily for 3-7 days, adjust dose according to response. Maintenance: 2 mg twice daily, start with lowest possible dose in elderly patients.
Adverse Effects
Postural hypotension, dizziness, lassitude, dry mouth, blurred vision, rash, vertigo, palpitations, dyspnoea, nasal congestion, GI upset, urinary frequency, oedema, asthaenia, fatigue, nervousness, drowsiness, headache, syncope.
Risk Factor (Pregnancy/Lactation)
Pregnancy: Risk cannot be ruled out. Lactation: Caution advised or effect undetermined. Contraindications: Congestive heart failure due to mechanical obstruction (e.g. aortic stenosis). History of micturition syncope. Precautions: The first dose may cause collapse due to hypotension therefore should be taken on retiring to bed. Cataract surgery, risk of intra-operative floppy iris syndrome. Monitor BP. Risk of priapism. Elderly.
Interactions
Other antihypertensives. PDE5 inhibitors.
Advice to Patient
Take with or without meals. It is best to take starting dose with dinner atleast 2-3 hours before sleeping. Contact prescriber if there is increased nervousness or depression, dizziness, rapid weight gain, rapid heartbeat or palpitations, muscle weakness, respiratory difficulty, fatigue, pain, hearing changes, vision changes or changes in urinary pattern. Avoid alcohol, standing for long time, exercise in hot weather during treatment. Weigh yourself in same dress at the same time of day once weekly. Change position slowly.
Pharmacokinetics
Onset: Hypertension: Within 30-90 mins after a single dose. CHF: Rapid. Duration: Hypertension: Single dose: 7-10 hrs. CHF: 6 hrs. Absorption: Readily absorbed from the GI tract. Metabolism: Hepatic (extensively). Bioavailability: Variable (43%-85% have been reported). Half-life elimination: 2-4 hrs. Heart failure patients: 7 hrs. Time to peak, plasma: Oral: 1-3 hrs. Excretion: Faeces via the bile (mainly). Urine (<10%).
Unlicensed Use
Children: Under 12 yr, not recommended. Hypertension: 1 mth-12 yr, 10-15 mcg/kg 2-4 times daily (initial dose at bedtime) increased gradually to max. 500 mcg/kg daily in divided doses (not exceeding 20 mg daily.
Brands with this active ingredient
Compiled by Healify Pharmacy from published drug references. How we compile it →
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