Medications with Alpha-Blocking Properties
Alpha-blocking medications include alpha-1 selective blockers (tamsulosin, silodosin), non-selective alpha-1 blockers (doxazosin, terazosin, alfuzosin), and combined alpha/beta blockers (carvedilol, labetalol). 1
Classification of Alpha Blockers
Alpha-1 Selective Blockers
- Tamsulosin: Selective for alpha-1A receptors, commonly used for BPH with minimal blood pressure effects 2
- Silodosin: Highly selective for alpha-1A receptors, with favorable cardiovascular safety profile 3
Non-Selective Alpha-1 Blockers
- Doxazosin: Used for both hypertension and BPH 1
- Terazosin: Effective for hypertension and BPH 4
- Alfuzosin: Lower rate of orthostatic hypotension compared to other non-selective agents 5
Combined Alpha and Beta Blockers
- Carvedilol: Blocks both alpha-1 and beta receptors, preferred in patients with heart failure 1
- Labetalol: Combined alpha-1 and beta-blocker, used primarily for hypertension 1
- Carvedilol phosphate: Extended-release formulation 1
Mechanism of Action
Alpha blockers work by blocking alpha-adrenergic receptors, which are found throughout the body:
- Alpha-1A receptors: Predominantly found in the prostate (approximately 70% of prostatic alpha-1 receptors) 2
- Alpha-1B receptors: Primarily found in vascular smooth muscle
- Alpha-1D receptors: Present in the bladder and spinal cord
By blocking these receptors, alpha blockers prevent norepinephrine from binding, resulting in:
- Relaxation of smooth muscle in the prostate and bladder neck
- Vasodilation in blood vessels (particularly with non-selective agents)
- Improved urinary flow in BPH patients
Clinical Differences Between Alpha Blockers
Cardiovascular Effects
- Selective alpha-1A blockers (tamsulosin, silodosin): Minimal effect on blood pressure, lower risk of orthostatic hypotension 6
- Non-selective alpha-1 blockers (doxazosin, terazosin): More significant blood pressure reduction, higher risk of orthostatic hypotension 7
- Alfuzosin: Despite being non-selective, has lower orthostatic hypotension risk than other non-selective agents 5
Sexual Side Effects
- Silodosin and tamsulosin: Higher rates of ejaculatory dysfunction (8-18% for tamsulosin, higher for silodosin) 5
- Doxazosin, terazosin, and alfuzosin: Lower rates of ejaculatory dysfunction 5
Central Alpha-2 Agonists with Alpha-Blocking Properties
These medications are generally reserved as last-line agents due to significant CNS side effects:
- Clonidine (oral and patch)
- Methyldopa
- Guanfacine 1
Clinical Considerations
Dosing
- Tamsulosin: 0.4mg daily, can be increased to 0.8mg if needed 2
- Doxazosin: 1-16mg daily 1
- Terazosin: 1-20mg daily or divided 1
- Alfuzosin: Slow-release formulation does not require dose titration 3
- Silodosin: Does not require dose titration 3
Special Populations
- Elderly patients: Alpha blockers are generally well-tolerated in men over 80 years, even with concomitant antihypertensive therapy 8
- Patients with planned cataract surgery: Should be informed about the risk of intraoperative floppy iris syndrome 1
Important Precautions
- First-dose phenomenon: Risk of significant hypotension with the first dose, particularly with non-selective agents
- Avoid abrupt discontinuation of beta-blockers with alpha-blocking properties (carvedilol, labetalol)
- Monitor for orthostatic hypotension, especially when initiating therapy or increasing dose
Choosing an Alpha Blocker
When selecting an alpha blocker, consider:
Cardiovascular status: For patients with cardiovascular concerns, tamsulosin or silodosin may be preferred due to their minimal effect on blood pressure 5
Sexual function concerns: For sexually active men concerned about ejaculatory function, doxazosin or alfuzosin may be better choices 5
Comorbid conditions:
- For patients with hypertension and BPH: doxazosin or terazosin may treat both conditions
- For patients with heart failure and hypertension: carvedilol is preferred 1
Alpha blockers remain first-line therapy for BPH and important agents for hypertension management, with selection guided by patient-specific factors and comorbidities.