prazosin

Absorption: 60% absorbed following oral administration.

Distribution: Widely distributed.

Protein Binding: 97%.

Metabolism/Excretion: Extensively metabolized by the liver. Minimal (5–10%) renal excretion of unchanged drug.

Half-Life: 2–3 hr.

Time/Action Profile ⬆ ⬇

(antihypertensive effects)

ROUTE	ONSET	PEAK	DURATION
PO	2 hr	2–4 hr‡	10 hr

‡Following single dose; maximal antihypertensive effects occur after 3–4 wk of chronic dosing.

Contraind./Precautions ⬆ ⬇

Contraindicated in:

Hypersensitivity.

Use Cautiously in:

Renal impairment (↑ sensitivity to effects; dose ↓ may be required);
Angina pectoris;
Patients undergoing cataract surgery (↑ risk of intraoperative floppy iris syndrome);
OB: Use during pregnancy only if potential maternal benefit justifies potential fetal risk; other antihypertensives preferred in pregnancy;
Lactation: Use while breastfeeding only if potential maternal benefit justifies potential risk to infant;
Pedi: Safety and effectiveness not established in children;
Geri: Appears on Beers list. risk of orthostatic hypotension in older adults. Avoid use for treatment of hypertension in older adults.

Adv. Reactions/Side Effects ⬆ ⬇

CV: first-dose orthostatic hypotension, palpitations, angina, edema, syncope

EENT: blurred vision, intraoperative floppy iris syndrome

GI: abdominal cramps, diarrhea, dry mouth, nausea, vomiting

GU: erectile dysfunction, priapism

Neuro: dizziness, headache, weakness, depression, drowsiness

Interactions ⬆ ⬇

Drug-drug:

Additive hypotension with acute ingestion of alcohol, other antihypertensives, or nitrates.
Antihypertensive effects may be ↓ by NSAIDs.

Route/Dosage ⬆ ⬇

Hypertension

PO (Adults ): 1 mg 2–3 times daily (give 1st dose at bedtime) for initial 3 days of therapy, then ↑ gradually to maintenance dose of 6–15 mg/day in 2–3 divided doses (not to exceed 20–40 mg/day).

Benign Prostatic Hyperplasia

PO (Adults ): 1–5 mg twice daily.

Availability ⬆ ⬇

(Generic available)

Capsules: 1 mg; 2 mg; 5 mg
Tablets: 1 mg; 2 mg; 5 mg

Assessment ⬆ ⬇

Assess for first-dose orthostatic reaction (dizziness, weakness) and syncope. May occur 30 min–2 hr after initial dose and occasionally thereafter. Incidence may be dose related. Volume-depleted or sodium-restricted patients may be more sensitive. Observe patient closely during this period; take precautions to prevent injury. 1st dose may be given at bedtime to minimize this reaction.
- Monitor intake and output ratios and daily weight; assess for edema daily, especially at beginning of therapy.
Hypertension: Monitor BP and pulse frequently during initial dose adjustment and periodically during therapy. Report significant changes.
- Monitor frequency of prescription refills to determine adherence.
Benign Prostatic Hyperplasia: Assess patient for symptoms of prostatic hyperplasia (urinary hesitancy, feeling of incomplete bladder emptying, interruption of urinary stream, impairment of size and force of urinary stream, terminal urinary dribbling, straining to start flow, dysuria, urgency) before and periodically during therapy.
- Rule out prostatic carcinoma before therapy; symptoms are similar.

Implementation ⬆ ⬇

May be used in combination with diuretics or beta blockers to minimize sodium and water retention. If these are added to prazosin therapy, reduce dose of prazosin initially and titrate to effect.
PO: Administer daily dose at bedtime, without regards to meals, at the same time each day. If necessary, dose may be increased to twice daily.

Patient/Family Teaching ⬆ ⬇

Instruct patient to take medication at the same time each day. Take missed doses as soon as remembered. If not remembered until next day, omit; do not double doses.
- Advise patient to weigh self twice weekly and assess feet and ankles for fluid retention.
- May cause dizziness or drowsiness. Advise patient to avoid driving or other activities requiring alertness until response to the medication is known.
- Caution patient to avoid sudden changes in position to decrease orthostatic hypotension. Alcohol, CNS depressants, standing for long periods, hot showers, and exercising in hot weather should be avoided because of enhanced orthostatic effects.
- Advise patient to notify health care professional of all Rx or OTC medications, vitamins, or herbal products being taken and to consult with health care professional before taking other medications, especially NSAIDs and cough, cold, or allergy remedies.
- Instruct patient to notify health care professional of medication regimen before any surgery.
- Advise patient to notify health care professional immediately if erection lasts for 4 hr or longer or if frequent dizziness, fainting, or swelling of feet or lower legs occurs.
- Advise females of reproductive potential to notify health care professional if pregnancy is planned or suspected or if breastfeeding.
- Emphasize the importance of follow-up exams to evaluate effectiveness of medication.
Hypertension: Emphasize the importance of continuing to take this medication as directed, even if feeling well. Medication controls but does not cure hypertension.
Encourage patient to comply with additional interventions for hypertension (weight reduction, low-sodium diet, smoking cessation, moderation of alcohol consumption, regular exercise, and stress management).
Instruct patient and family on proper technique for BP monitoring. Advise them to check BP at least weekly and to report significant changes.

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Pronunciation ⬇

Classifications ⬆ ⬇

Indications ⬆ ⬇

Action ⬆ ⬇

Pharmacokinetics ⬆ ⬇