Mechanism of Action

  • Dilation of the pupil is primarily controlled by the radial iris dilator muscles
    • These dilator muscles are activated by alpha-1 adrenergic agonists
  • Phentolamine reversibly blocks alpha-1 receptors on the iris dilator muscles, thereby:
    • Reducing pupil diameter
    • Directly antagonizing the mydriatic effect of an alpha-1 adrenergic agonist
    • Indirectly reversing mydriasis induced by muscarinic antagonist effects on the iris sphincter muscle
RYZUMVI® (phentolamine ophthalmic solution). Prescribing Information. Available at: https://www.ryzumvi.com/files/prescribing-information.pdf.