Understanding Alpha Blockers and Their Effects

Oct 1, 2024

Lecture Notes: Alpha Blockers

Introduction

  • Topic: Alpha blockers
  • Focus: Mechanism of action, types, indications, and side effects

Mechanism of Action

  • Primary Function: Block alpha receptors (alpha-1, alpha-2)
  • Alpha-1 Receptors:
    • Located on vascular smooth muscle
    • Epinephrine/Norepinephrine: Cause vasoconstriction -> increased total peripheral resistance, increased afterload, and blood pressure
    • Alpha Blockers: Prevent binding -> vasodilation -> decreased total peripheral resistance and afterload -> reduced blood pressure

Therapeutic Uses

  • Hypertension: Decrease blood pressure
  • Benign Prostatic Hyperplasia (BPH):
    • Relax internal urethral sphincter -> improve urine flow
  • Selective Alpha-1 Blockers: Terazosin, Doxazosin, Prazosin, Tamsulosin

Detailed Mechanism

  • Smooth Muscle Cells:
    • Calcium Role: Binds calmodulin -> activates myosin light-chain kinase -> muscle contraction
    • Alpha Blockers: Reduce calcium entry and phosphorylation -> smooth muscle relaxation

Non-Selective Alpha Blockers

  • Types:
    • Phenoxybenzamine: Irreversible allosteric inhibitor
    • Phentolamine: Reversible active site inhibitor
  • Usage:
    • Treat pheochromocytoma (tumor secreting high epinephrine/norepinephrine)

Indications

  • Hypertension: Second-line or with BPH
  • BPH: Relieve urinary retention
  • Ureteral Calculi: Facilitate passing kidney stones
  • Pheochromocytoma: Reduce blood pressure
  • Hypertensive Crisis: Due to monoamine oxidase inhibitors
  • Cocaine/Methamphetamine Use: Control hypertension

Side Effects

  • Vasodilation Effects:
    • Hypotension
    • Peripheral edema
    • Reflex tachycardia
    • Flushing
  • Ocular Effects:
    • Intraoperative floppy iris syndrome (IFIS) during cataract surgery
  • Urinary Effects:
    • Increased urinary frequency
    • Risk of urinary incontinence
  • Reproductive Effects:
    • Retrograde ejaculation
    • Decreased ejaculatory response

Contraindications

  • Cataract Surgery: Avoid tamsulosin (risk of IFIS)
  • Urinary Incontinence: Avoid alpha blockers (risk of worsening condition)

Conclusion

  • Alpha blockers: Used for managing hypertension and BPH, among other indications
  • Importance of understanding the side effects and contraindications
  • Note: Check social media links for additional resources

End of Lecture

Study Tips:

  • Remember key differences between selective and non-selective alpha blockers.
  • Understand the physiological effects of alpha-1 receptor blockade in various tissues.