title: pH and drug ionization affects ocular pressure lowering of topical carbonic anhydrase inhibitors.
abstract: OBJECTIVE
  To evaluate the effect of drug ionization on the ocular hypotensive activity of topical carbonic anhydrase inhibitors.
  
  
  METHODS
  Ocular normotensive New Zealand albino and ocular hypertensive Dutch Belted pigmented rabbits were used. Tonometric intraocular pressure levels were taken after topical application of 50 microliters of drug (at various concentrations and pH values) to one eye with the contralateral eye used as an untreated control. The drugs tested were MK-927, L-662,583, and AHR-16329. Eye tissues were analyzed for drug by our enzymatic methods.
  
  
  RESULTS
  In all cases, the more ionized the applied drug the greater the ocular hypotensive activity. Tissue distribution studies showed that there was more drug found in the eye after the ionized form of a drug was applied than that found after application of the less ionized forms.
  
  
  CONCLUSIONS
  Increasing the ionization of three ampholyte topical carbonic anhydrase inhibitors increases their ocular hypotensive activity. These data taken with ocular disposition data suggest that ionized compounds of this type are more readily sequestered in the cornea, which serves as a drug depot for prolonged drug delivery and activity.
authors.affiliation: University of Florida Health Science Center, Department of Pharmacology and Therapeutics, Gainesville 32610.
authors.forename: W F
authors.initials: WF
authors.lastname: Brechue
authors.forename: T H
authors.initials: TH
authors.lastname: Maren
mesh_terms: D000818:Animals; D002257:Carbonic Anhydrase Inhibitors / Q000493:pharmacokinetics / Q000494:pharmacology*; D005123:Eye / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles / Q000493:pharmacokinetics / Q000494:pharmacology; D007429:Intraocular Pressure / Q000187:drug effects*; D008297:Male; D009798:Ocular Hypertension / Q000503:physiopathology; D009883:Ophthalmic Solutions; D009994:Osmolar Concentration; D011817:Rabbits; D012995:Solubility; D013449:Sulfonamides / Q000493:pharmacokinetics / Q000494:pharmacology; D013876:Thiophenes / Q000493:pharmacokinetics / Q000494:pharmacology
chemical_list: D002257:Carbonic Anhydrase Inhibitors; D007093:Imidazoles; D009883:Ophthalmic Solutions; D013449:Sulfonamides; D013876:Thiophenes; C063960:L 662583; C079772:AHR 16329; C057921:sezolamide