Terazosin has a peripheral post-synaptic alpha 1-blocking action. Terazosin produces vasodilation and reduces peripheral resistance but generally has little effect on cardiac output.Antihypertensive effect with chronic dosing is usually not accompanied by reflex tachycardia . Relaxation of smooth muscle in the bladder neck, prostate and prostate capsule produced by alpha 1-adrenergic blockade results in a reduction in urethral resistance and pressure, bladder outlet resistance and urinary symptoms.

Mild to moderate hypertension; Benign prostatic hyperplasia (BPH).

a- > 10 %: Dizziness; Headache; Muscle weakness
b- 1% to 10%: Edema; Palpitations; Chest pain ; Peripheral edema ; Orthostatic hypotension; Tachycardia; Fatigue; Nervousness; Drowsiness; Dry mouth; Urinary incontinence; Blurred vision; Dyspnea; Nasal congestion
c- <1% (Limited to important or life – threatening ): Allergic reactions; Anaphylaxis; Atrial fibrillation; Priapism; Sexual dysfunction; Syncope; Thrombocytopenia.

Hypersensitivity to quinazolines ( doxazosin, prazosin, terazosin) or any component of the formulations.

Terazosin can cause significant orthostatic hypotension and syncope,especially with first dose. Prostate cancer should be ruled out before starting for BPH. Anticipate a similar effect if therapy is interrupted for a few days , if dosage is rapidly increased , or if another antihypertensive drug is introduced.

Hypotensive effect of Terazosin may be increased by ACE inhibitors, beta – blockers and calcium channel blockers. NSAIDs , especially indomethacin may antagonize the antihypertensive effect of terazosin by inhibiting renal prostaglandin synthesis and/or by causing sodium and fluid retention . Antihypertensive effects of terazosin may be reduced when it is used concurrently with sympathomimetics . Concurrent use of terazosin antagonizes the peripheral vasoconstriction produced by high doses of dopamine. Concurrent use of terazosin may decrease the pressor response to ephedrine . Concurrent use of terazosin may block the alpha – adrenergic effects of epinephrine , possibly resulting in severe hypotension and tachycardia . Concurrent use of terazosin usually decreases the pressor effect of metaraminol . Prior administration of terazosin may decrease the pressor effect and shorten the duration of action of methoxamine and phenylephrine. Blood pressure – lowering effects of sildenafil and vardenafil are additive;therefore use of vardenafil is contraindicated and use of sildenafil is recommended with extreme caution during treatment with terazosin.

Standing and sitting /supine blood pressure , especially following the initial dose at 2-4 hours following the dose ; urinary symptoms.

Terazosin may be taken without regard to meals.

• Usual adult and adolescent dose:
  Antihypertensive – Initial : Oral , 1 mg once a day , at bedtime.
  Maintenance: Oral , adjusted gradually to meet individual requirement , usually 1 to 5 mg once a day.
  Note: If the antihypertensive effect is not maintained for a full 24 hours , twice daily dosing may be more effective.
  Benign prostatic hyperplasia – Initial: Oral , 1 mg once a day . at bedtime.
  Maintenance: Oral , adjusted gradually up to 5 to 10 mg once a day, Doses of 10 mg once a day are generally required for an adequate response.
• Usual adult prescribing limits: Daily doses higher than 20 mg usually do not have increased efficacy.
• Usual pediatric dose: Safety and efficacy have not been established.

• USP DI, 2004
• Up To Date, Vol. 13.1 (2005)
• Martindale, The Complete Drug Reference, 33 rd edition 2002