Introduction
Terazosin hydrochloride is a selective alpha-1 adrenergic receptor antagonist belonging to the quinazoline class of compounds. Originally developed and approved by the FDA in 1987, it is commonly prescribed for the management of hypertension and benign prostatic hyperplasia (BPH). As a long-acting alpha-blocker, terazosin offers the advantage of once-daily dosing, improving patient compliance compared to shorter-acting alternatives.
Mechanism of Action
Terazosin selectively and competitively inhibits postsynaptic alpha-1 adrenergic receptors, primarily located in vascular smooth muscle and the prostate. This blockade results in:
For hypertension: Vasodilation of both arterial and venous systems, reducing peripheral vascular resistance and blood pressure For BPH: Relaxation of smooth muscle in the prostate capsule and bladder neck, decreasing urinary outflow resistance and improving urinary flow ratesThe drug exhibits greater selectivity for alpha-1 receptors than alpha-2 receptors (approximately 12:1 ratio), minimizing effects on presynaptic negative feedback mechanisms.
Indications
1. Hypertension: Management of mild to moderate hypertension, either as monotherapy or in combination with other antihypertensive agents 2. Benign Prostatic Hyperplasia (BPH): Treatment of symptomatic BPH to improve urinary symptoms and flow rates 3. Off-label uses: Management of ureteral calculi, neurogenic bladder, and autonomic dysreflexia (though evidence is limited)
Dosage and Administration
Hypertension:- Initial dose: 1 mg orally at bedtime
- Maintenance dose: 1-5 mg once daily (maximum 20 mg daily)
- Titration: Increase gradually at intervals of at least 2 weeks
- Initial dose: 1 mg orally at bedtime
- Maintenance dose: 5-10 mg once daily (maximum 20 mg daily)
- Titration: Increase gradually based on symptom response and tolerability
- Renal impairment: No dosage adjustment typically required
- Hepatic impairment: Use with caution; consider reduced dosing
- Geriatric patients: Start with lowest possible dose due to increased sensitivity
- Pediatric use: Safety and effectiveness not established
- Take at the same time each day, preferably at bedtime
- May be taken with or without food
- Capsules should be swallowed whole
Pharmacokinetics
Absorption: Well absorbed from GI tract; bioavailability approximately 90% Distribution: Volume of distribution ~0.6 L/kg; 90-94% protein bound Metabolism: Extensively metabolized in liver via hepatic conjugation and oxidation Elimination: Half-life 9-12 hours; excreted primarily in feces (60%) and urine (40%) Onset of action: 15 minutes for blood pressure effects; 2 weeks for BPH symptom improvement Duration of action: 24 hoursContraindications
1. Hypersensitivity to terazosin, other quinazolines, or any component of the formulation 2. Concurrent use with phosphodiesterase-5 inhibitors (e.g., sildenafil, tadalafil) due to risk of severe hypotension 3. Patients with a history of orthostatic hypotension 4. Severe hepatic impairment
Warnings and Precautions
First-dose effect: Significant hypotension and syncope may occur within 30-90 minutes after initial dose or dosage increases Orthostatic hypotension: Risk particularly in elderly and volume-depleted patients Intraoperative floppy iris syndrome: May occur during cataract surgery Priapism: Rare reports requiring immediate medical attention Prostate cancer: Symptoms of BPH and prostate cancer are similar; proper diagnosis essential Use in pregnancy: Category C - use only if potential benefit justifies potential risk Driving caution: May cause dizziness or drowsiness affecting ability to operate machineryDrug Interactions
Significant interactions:- Other antihypertensives: Additive hypotensive effects
- Phosphodiesterase-5 inhibitors: Profound hypotension
- Alcohol: Enhanced hypotensive and CNS effects
- NSAIDs: May reduce antihypertensive efficacy
- Beta-blockers, calcium channel blockers: Enhanced hypotensive effects
- Sildenafil, vardenafil, tadalafil: Contraindicated combination
Adverse Effects
Common (≥5%):- Dizziness (19%)
- Asthenia (11%)
- Headache (9%)
- Somnolence (5%)
- Nasal congestion (6%)
- Peripheral edema (5%)
- Syncope (1%)
- Palpitations (5%)
- Orthostatic hypotension (5%)
- Priapism (<1%)
- Vision abnormalities (2%)
- Nausea, vomiting
- Dyspnea
- Weight gain
- Blurred vision
- Impotence (2%)
Monitoring Parameters
Baseline:- Blood pressure (standing and supine)
- Heart rate
- Prostate-specific antigen (PSA) if BPH indication
- Renal and hepatic function tests
- Symptom score assessment (IPSS for BPH)
- Blood pressure at each visit (especially after dose changes)
- Orthostatic blood pressure measurements
- BPH symptom assessment every 3-6 months
- Adverse effect monitoring
- Regular eye examinations in patients considering cataract surgery
- Blood pressure if prescribed for hypertension
- Urinary symptoms if prescribed for BPH
- Signs of dizziness or lightheadedness
Patient Education
Key points to communicate:1. Take first dose at bedtime to minimize risk of fainting 2. Rise slowly from sitting or lying position to prevent dizziness 3. Avoid driving or operating machinery until effects are known 4. Do not stop taking suddenly without medical advice 5. Report any prolonged or painful erections immediately 6. Inform all healthcare providers about terazosin use, especially before surgery 7. Avoid alcohol as it may increase side effects 8. Be consistent with timing of administration 9. Monitor for symptoms of low blood pressure (dizziness, lightheadedness) 10. Keep regular follow-up appointments with healthcare provider
Storage:- Store at room temperature (15-30°C)
- Keep in original container away from moisture
- Keep out of reach of children
References
1. FDA Prescribing Information: Terazosin Hydrochloride Capsules 2. Chapple CR et al. Terazosin in the treatment of benign prostatic hyperplasia. Drugs. 1996 3. Grimm RH et al. Antihypertensive therapy and quality of life. Am J Hypertens. 1997 4. Kaplan SA. Alpha-blocker therapy: current update. Rev Urol. 2005 5. Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure. JNC 8 Guidelines. 2014 6. American Urological Association Guideline: Management of Benign Prostatic Hyperplasia. 2019 7. Micromedex® Healthcare Series. IBM Watson Health 8. Lexicomp® Online. Wolters Kluwer Health 9. Clinical Pharmacology [Internet]. Tampa (FL): Elsevier
This information is intended for educational purposes only and should not replace professional medical advice. Always consult with a qualified healthcare provider for personalized medical guidance.