Randhawa M A, Khan M M A, Malik Shah Zaman Latif, Alvi T A, Imran K M, Shabana A, Baig N, Malik S A, Yousaf S M.
Ionization of Quaternary Amines does not Affect Their Diffusion Across Cornea / Conjunctiva.
J Rawal Med Coll Jan ;2(1-2):22-8.

Tertiary amines, being less ionized in solution, are said to be more lipid soluble and easy to cross body membranes. Quaternary amines, being more ionized in solution, are said to be less lipid soluble and difficult to cross body membranes. But it has been reported that the diffusion of drugs across buccal mucosa and renal tubular membrane is not related to their pKa values and the degree of ionization as calculated from the Henderson-Hasselbalch Equation Ratio unionized/ionized. When the membrane diffusion of drugs is not related to their degree of ionization and pKa values, it was anticipated that ionization of quaternary amines should also not affect their membrane transport. We compared the effect of quaternary amines constrictors and dilators of pupil on intact rabbit eye with their tertiary amine counterparts. We measured the mean change in pupil size from 0 to 240 minutes with serial dilutions of these drugs. We plotted their graded dose response curves at the peak effect and calculated the ED50s and dose ratios. We found that quaternary amines constrictors and dilators of pupil in equal or even lower concentrations produced similar effects to tertiary amines. It was concluded that ionization of quaternary amines does not affect their transport across cornea/conjunctiva and action on pupil size.

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