title: Dosage variability of topical ocular hypotensive products: a densitometric assessment.
abstract: OBJECTIVE
  To ascertain consequence of variability in drop volume obtained from multiuse topical ocular hypotensive products in terms of uniformity of product dosage.
  
  
  METHODS
  Densitometric assessment of drop volume dispensed from 2 alternative bottle positions.
  
  
  RESULTS
  All except one product demonstrated a statistically significant difference in drop volume when administered at either a 45-degree or 90-degree bottle angle (Student t test, P<0.001). Product-specific drop volume ranged from a nadir of 22.36 microL to a high of 53.54 microL depending on bottle angle of administration. Deviation in drop dose was directly proportional to variability in drop volume. Variability in per drop dosage was conspicuous among products with a coefficient of variation from 1.49% to 15.91%. In accordance with drop volume, all products demonstrated a statistically significant difference in drop dose at 45-degree versus 90-degree administration angles. Drop volume was found unrelated to drop uniformity (Spearman r=0.01987 and P=0.9463).
  
  
  CONCLUSIONS
  Variability and lack of uniformity in drop dosage is clearly evident among select ocular hypotensive products and is related to angle of drop administration. Erratic dosage of topical ocular hypotensive therapy may contribute in part to therapeutic failure and/or toxicity.
authors.affiliation: Department of Ophthalmology, Rush College of Medicine, Chicago, IL 60612, USA. bgaynes@rush.edu
authors.forename: Bruce I
authors.initials: BI
authors.lastname: Gaynes
authors.forename: Ramesh M
authors.initials: RM
authors.lastname: Singa
authors.forename: Ying
authors.initials: Y
authors.lastname: Cao
mesh_terms: D000287:Administration, Topical; D000959:Antihypertensive Agents / Q000008:administration & dosage*; D003720:Densitometry / Q000379:methods*; D004349:Drug Packaging / Q000592:standards*; D005901:Glaucoma / Q000188:drug therapy; D006801:Humans; D009883:Ophthalmic Solutions / Q000008:administration & dosage*; D015203:Reproducibility of Results
chemical_list: D000959:Antihypertensive Agents; D009883:Ophthalmic Solutions