USMLE

PDE-5 Inhibitors (Sildenafil, Vardenafil, Tadalafil)

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Reproductive Pharm
  1. Leuprolide
  2. Anastrozole
  3. Estrogens
  4. Clomiphene
  5. Progestins
  6. Mifepristone
  7. Copper IUDs
  8. Danazol
  9. Terbutaline, Ritodrine
  10. Minoxidil
  11. Androgens (Testosterone, Methyltestosterone)
  12. Flutamide
  13. PDE-5 Inhibitors (Sildenafil, Vardenafil, Tadalafil)
  14. Finasteride

Summary

PDE-5 inhibitors are a group of drugs ending in the common suffix “-afil”, including Sildenafil, Vardenafil, and Tadalafil. These drugs work by inhibiting the phosphodiesterase-5 enzyme, increasing levels of cyclic GMP and causing vasodilation through nitric oxide. This vasodilation induced by PDE-5 inhibitors is useful for the treatment of erectile dysfunction and pulmonary hypertension. However, systemic vasodilation may also lead to the side effect of life-threatening hypotension, especially when taken with nitrates.

Key Points

  • PDE-5 inhibitors
    • Drug Names
      • - “fil” suffix (Sildenafil, Vardenafil, Tadalafil)
    • Mechanism
      • Inhibit phosphodiesterase inhibitors-5 (PDE-5) →  increased cyclic GMP
        • PDE5 inhibitors reduce degradation of cGMP, which enhances vasodilation of nitric oxide (NO)
    • Indications
      • Erectile dysfunction 
        • Increase vasodilatory effects increase blood flow to penis causing erections
      • Pulmonary hypertension
        • Increase vasodilatory effects reduce vascular resistance in lung, improving symptoms
      • Benign Prostatic Hyperplasia
        • Tadalafil used in this context to improve urine output
    • Adverse Effects
      • Causes Hypotension
        • Systemic vasodilation by NO reduces systemic vascular resistance, which can cause a precipitous drop in blood pressure
        • Absolute contraindication with nitrates
          • Nitrates are converted into NO to function, which acts synergistically with PDE5 inhibitors to cause life-threatening hypotension
      • Causes Cyanopia (blue-tinted vision)
      • Causes Headache, flushing, dyspepsia also seen