What is the difference between Terazosin (alpha-1 blocker) and Prazosin (alpha-1 blocker) in treating Hypertension (high blood pressure) or Benign Prostatic Hyperplasia (BPH)?

Terazosin vs Prazosin: Key Differences

For BPH, use terazosin—prazosin lacks sufficient evidence and is not recommended by guidelines; for hypertension, terazosin offers superior once-daily dosing compared to prazosin's 2-3 times daily requirement, though both are second-line agents. 1, 2

Critical Guideline-Based Recommendations

For Benign Prostatic Hyperplasia (BPH)

Terazosin is an appropriate first-line treatment option for BPH, while prazosin explicitly lacks sufficient data to support its use. 1

• The American Urological Association guidelines clearly state that data are insufficient to support prazosin use for BPH 1, 2
• Terazosin (along with alfuzosin, doxazosin, and tamsulosin) has established efficacy with 4-6 point improvements in AUA Symptom Index, which patients perceive as meaningful change 1
• Terazosin dosing is titrated up to 10 mg for maximum efficacy, with dose-dependent effectiveness 1
• The lack of rigorous clinical trial data is the specific reason prazosin is excluded from BPH treatment recommendations 2, 3

For Hypertension

Both agents are approved for hypertension but are second-line due to orthostatic hypotension risk; terazosin's pharmacokinetic advantage of once-daily dosing makes it preferable. 3, 4

• Prazosin requires 2-3 times daily dosing (2-20 mg/day) for adequate 24-hour blood pressure control 2, 3
• Terazosin allows once-daily dosing due to its elimination half-life being 3-4 times longer than prazosin (approximately 12 hours vs 3-4 hours) 4, 5, 6
• Terazosin has 25 times greater water solubility than prazosin, facilitating more complete and predictable gastrointestinal absorption 5, 6
• Both agents should not be relied upon as sole therapy for hypertension in patients with cardiac risk factors, as alpha-blockers may increase congestive heart failure risk 1

Pharmacokinetic Distinctions

The fundamental difference is terazosin's longer half-life enabling once-daily administration, improving compliance. 4, 5

• Terazosin's terminal-phase plasma half-life is approximately 12 hours 6, 7
• Prazosin's shorter half-life necessitates multiple daily doses to maintain therapeutic effect 4, 5
• Terazosin's more predictable absorption may facilitate easier dose titration compared to prazosin 6

Shared Adverse Effect Profile

Both agents share similar side effects as alpha-1 blockers, though frequency may differ:

• Primary adverse events include orthostatic hypotension, dizziness, asthenia, and nasal congestion 1
• First-dose syncope risk requires initial dosing at bedtime for both agents 2, 6
• Elderly patients and those on multiple medications face highest risk for orthostatic hypotension and falls 2
• Terazosin may have slightly lower first-dose syncope incidence compared to prazosin 6

Lipid Profile Effects

Both agents demonstrate favorable effects on lipid profiles, unlike diuretics and beta-blockers. 6, 7

• Terazosin reduces total cholesterol and LDL+VLDL fractions while tending to increase HDL cholesterol 6, 7
• These beneficial lipid changes represent a potential cardiovascular advantage over other antihypertensive classes 7

Specific Clinical Scenarios

When Prazosin Is Appropriate

Prazosin has Level A evidence for PTSD-associated nightmares, an indication terazosin does not have:

• Dosing starts at 1 mg at bedtime, titrating by 1-2 mg every few days to average effective dose of 3 mg (range up to 9.5-13.3 mg/day for severe cases) 2, 3

Common Pitfalls to Avoid

• Do not prescribe prazosin for BPH—guidelines are explicit that evidence is insufficient; use terazosin, doxazosin, tamsulosin, or alfuzosin instead 2, 3
• Do not assume once-daily prazosin is adequate for hypertension—it requires 2-3 times daily dosing for 24-hour control 2, 3
• Do not combine with other CNS depressants without caution—additive sedation and orthostatic hypotension may occur 2, 3
• Avoid abrupt discontinuation of either agent, though neither causes withdrawal phenomena like clonidine 2

Practical Dosing Algorithm

For BPH: Start terazosin 1 mg at bedtime, titrate gradually as blood pressure stabilizes at each dose level up to 10 mg daily for optimal symptom control 1, 6

For hypertension: Terazosin 1 mg at bedtime initially, titrating up to maximum 20 mg daily as needed; prazosin requires divided dosing 2-3 times daily 2, 6