Alpha Blockers

Mechanism of action

• α-blockers are pharmacological agents that act as neutral antagonists or inverse agonists of α-adrenergic receptors
• Blocks Alpha-1 receptors in blood vessels (arteries and veins). By blocking these receptors, blood vessels will dilate (relax) and lower blood pressure.

Treatment

• High blood pressure (hypertension)
• Benign prostate hyperplasia
• Raynaud syndrome
  • spasm of arteries causes periods of reduced blood flow
• Scleroderma
  • Autoimmune diseases which cause changes to changes to the skin, blood vessels, muscles, and internal organs

Names of Selective α1-adrenergic Receptor Antagonists

• Alfuxosin (Uroxatral, Xat, Xatral, Prostetrol and Alfural)
• Doxazosin (Cardura)
  • Increased cardiac output during exercise at 50% VO2 Max (ACSM 2013)
  • No change of heart rate during exercise up to 50% VO2 Max (ACSM 2013)
  • Increase of heart rate during exercise at 75% VO2 Max (ACSM 2013)
• Prazosin (Minipress)
  • Acute administration (ACSM 2013)
    • Increased heart rate during exercise
  • Chronic administration (ACSM 2013)
    • No change during exercise
• Tamsulosin (Flomax)
• Terazosin (Hytrin)
• Silodosin (Rapaflo, Silodyx, Rapilif, Silodal, Sildoo, Urief, Thrupas, Urorec)

Effect on Exercise and Rest

• No effect on heart rate (Niedfeldt 2002, ACSM 2013)
• Decrease of systolic blood pressure (ACSM 2013)
• No change of diastolic blood pressure (ACSM 2013)
• No effect on stroke volume (Niedfeldt 2002)
• No effect on cardiac output (Niedfeldt 2002)
• Decrease in vascular resistance (Niedfeldt 2002)
• No effect on plasma volume (Niedfeldt 2002)
• Decreased exercise ischemia (ACSM 2013)
• No effect on training (Niedfeldt 2002)
• No effect on performance (ACSM 2013)

Potential Side Effect

• First-dose hypotensive effect with alpha-1 blockers especially in elderly patients (Niedfeldt 2002)
• Centrally acting agents may cause drowsiness, dry mouth, and impotence (Niedfeldt 2002)
• Rebound hypertension can occur with abrupt discontinuation of clonidine (Catapres), an alpha agonist (Niedfeldt 2002)

Recommended Populations

• Recommended for those with hyperlipidemia or benign prostatic hyperplasia (BPH) (Niedfeldt 2002)

Populations Not Recommend

• Not recommended for men older than 55 (Niedfeldt 2002)

Banned Status

• None

References

American College of Sports Medicine (2013). Guidelines for Exercise Testing and Prescription, William & Wilkins, 9, 402.

Niedfeldt MW (2002). Managing Hypertension in Athletes and Physically Active Patients. Am Fam Physician. 1;66(3):445-453.