terazosin (Rx)

>10%

Dizziness (10-20%)

Asthenia (2-13%)

1-10%

Hypotension (3-7%)

Rhinitis/nasal congestion (2-6%)

Lightheadedness (3-5%)

Somnolence (3-5%)

Palpitation (4%)

Nausea (2-4%)

Edema (3%)

Sinusitis (3%)

Dyspnea (2-3%)

Fatigue (2.5%)

Headache (2.5%)

Back pain (2.4%)

Flulike syndrome (2.4%)

Tachycardia (2%)

Amblyopia (1-2%)

Blurred vision (1-2%)

Impotence (1-2%)

Syncope (1%)

Contraindications

Hypersensitivity to terazosin, other quinazolines

Cautions

Carcinoma of the prostate and BPH cause many of the same symptoms; these two diseases frequently co-exist; patients thought to have BPH should be examined prior to starting therapy to rule out presence of carcinoma of the prostate

Therapy can cause marked lowering of blood pressure, especially postural hypotension, and syncope in association with first dose or first few days of therapy; a similar effect can be anticipated if therapy is interrupted for several days and then restarted; to decrease likelihood of syncope or excessive hypotension, treatment should always be initiated at a low dose (1 mg) and increased slowly; additional antihypertensive agents should be added with caution; patient should be cautioned to avoid situations, such as driving or hazardous tasks, where injury could result should syncope occur during initiation of therapy

If syncope occurs, the patient should be placed in a recumbent position and treated supportively as necessary; there is evidence that orthostatic effect is greater, even in chronic use, shortly after dosing; the risk of the events is greatest during initial seven days of treatment, but continues at all time intervals

While syncope is the most severe orthostatic effect, other symptoms of lowered blood pressure, such as dizziness, lightheadedness and palpitations, are more common; patients with occupations in which such events represent potential problems should be treated with particular caution

May cause CNS depression, which may impair physical or mental abilities; use caution when performing tasks that may require mental alertness, including driving or operating heavy machinery

May exacerbate heart failure

Concomitant administration with PDE-5 inhibitor (eg, sildenafil) can result in additive blood pressure-lowering effects and symptomatic hypotension; initiate PDE-5 inhibitor therapy at lowest dose

Risk of priapism (rare); because this condition can lead to permanent impotence if not promptly treated, patients must be advised about seriousness of the condition

Pregnancy category: C

Lactation: Not known if excreted into breast milk; use caution

Pregnancy Categories

A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.

B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.

C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.

D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.

X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.

NA: Information not available.

Mechanism of Action

Blocks postsynaptic alpha-1 receptor; alpha blockade causes arterial and venous dilation

Selective agents cause less tachycardia than do nonselective agents

Absorption

Bioavailability: 90%

Onset (hypertension): 3 hr

Onset (benign prostate hyperplasia): 2 weeks

Duration: 24 hr

Peak response (benign prostate hyperplasia): 4-6 weeks

Peak plasma time: 1 hr

Distribution

Protein bound: 90-94%

Vd: 25-30 L

Metabolism

Metabolized extensively via hydrolysis, O-demethylation, and N-dealkylation in liver

Metabolites: 6- and 7-O-demethyl terazosin, piperazine derivative, diamine metabolite

Elimination

Half-life: 9-12 hr

Renal clearance: 9-12.5 mL/min

Excretion: Feces (55-60%); urine (40%)