title: The physical properties of generic latanoprost ophthalmic solutions are not identical.
abstract: OBJECTIVE
  To compare various characteristics of Xalatan®and five generic latanoprost ophthalmic solutions.
  
  
  METHODS
  Drop size, volume, pH values, buffer capacity, viscosity, hardness of bottles and costs were determined. Drop sizes were measured in triplicates by micropipettes, and the number of drops counted in three separate bottles of each generic product was determined. pH values were measured in triplicates by a calibrated pH meter. Buffer capacity was exploited by titrating known quantities of strong base into 2.5 ml of each brand and interpolated to neutral pH. Kinematic viscosity was determined by linear regression of timed gravity flow from a vertical syringe through a 21-G cannula. The hardness of the bottles was evaluated by gradually increasing tension on a hook placed around each bottle until a drop was expelled reading the tension on an attached spring scale.
  
  
  RESULTS
  Drop sizes and the number of drops in the bottles varied significantly between the generic drugs. The control value of pH in the brand version (Xalatan®) was markedly lower compared to the generic latanoprost products. Titration of Xalatan®to neutrality required substantially more NaOH compared to the generic latanoprost products. Finally, the viscosity revealed a significant variability between brands. Remarkable differences were found in bottle shapes, bottle hardness and costs of the latanoprost generics.
  
  
  CONCLUSIONS
  Generic latanoprost eye drops should not be considered identical to the original brand version as regards to drop size, volumes, pH values, buffer capacity, viscosity, hardness of bottles and costs. It is likely that these issues affect compliance and intraocular pressure (IOP)-lowering effect. Therefore, re-evaluation of the requirements for introducing generic eye drops seems reasonable.
authors.affiliation: Department of Ophthalmology, Zealand University Hospital, Roskilde, Denmark.|Department of Drug Design and Pharmacology, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Miriam
authors.initials: M
authors.lastname: Kolko
authors.affiliation: Department of Ophthalmology, Zealand University Hospital, Roskilde, Denmark.
authors.forename: Peter
authors.initials: P
authors.lastname: Koch Jensen
mesh_terms: D000959:Antihypertensive Agents / Q000008:administration & dosage / Q000737:chemistry; D016527:Drug Costs; D016568:Drugs, Generic; D005901:Glaucoma / Q000188:drug therapy* / Q000503:physiopathology; D006801:Humans; D007429:Intraocular Pressure / Q000187:drug effects*; D000077338:Latanoprost; D009883:Ophthalmic Solutions; D011461:Prostaglandins F, Synthetic / Q000008:administration & dosage / Q000737:chemistry* / Q000191:economics; D014065:Tonometry, Ocular
chemical_list: D000959:Antihypertensive Agents; D016568:Drugs, Generic; D009883:Ophthalmic Solutions; D011461:Prostaglandins F, Synthetic; D000077338:Latanoprost
keywords: generic drugs; glaucoma; latanoprost