title: Determination of phosphate concentration in glaucoma eye drops commercially available in Spain.
abstract: OBJECTIVE
  To identify and analyze the phosphate concentration in glaucoma eye drops available in Spain.
  
  
  METHODS
  Glaucoma medications containing phosphates were identified according to the 2013 Vademecum and the website of the Spanish Agency for Medicines and Medical Devices. Phosphate concentration was determined in these eye drops using ultraviolet molecular absorption spectrophotometry, and pH was determined using scan image analysis algorithms of pH strips.
  
  
  RESULTS
  A total of 37 phosphate containing glaucoma eye drops were identified. The mean phosphate concentration was 97.72±75.52mM. The group with higher concentration of active substance was timolol (204.85±42.38mM) followed by brimonidine/timolol (200.9mM). No statistically significant difference was found between brand name (95.65±71.11mM) and generic eye drops (99.14±80mM, P=.892). Although no statistically significant difference was found between products containing preservatives (99.24±76.78mM) and those without preservatives (85.17±72.86mM) (P=.730), a lower phosphate concentration was observed in the preservative-free Timolol and Latanoprost. Single dose samples showed a lower phosphate concentration than multi-dose ones (102.04±75.39 vs. 22.24±2.98mM, P<.001). The mean pH was 7.13±0.63. No statistical correlation was found between phosphate concentration and pH (r: 0.07).
  
  
  CONCLUSIONS
  The phosphate concentration in glaucoma eye drops exceeded the tear film physiological level (1.45mM). No difference was observed between brand names and generic eye drops. Lower phosphate concentration was observed in preservative-free single dose eye drops.
authors.affiliation: Servicio de Oftalmología, Hospital Universitario Donostia, San Sebastián (Guipúzcoa), España. Electronic address: imarsoroa@hotmail.com.
authors.forename: I
authors.initials: I
authors.lastname: Martínez-Soroa
authors.affiliation: Servicio de Oftalmología, Hospital Universitario Donostia, San Sebastián (Guipúzcoa), España.
authors.forename: M
authors.initials: M
authors.lastname: de Frutos-Lezaun
authors.affiliation: Departamento de Química Analítica, Facultad de Químicas, Universidad del País Vasco, San Sebastián (Guipúzcoa), España.
authors.forename: M
authors.initials: M
authors.lastname: Ostra Beldarrain
authors.affiliation: Departamento de Química Analítica, Facultad de Químicas, Universidad del País Vasco, San Sebastián (Guipúzcoa), España.
authors.forename: A
authors.initials: A
authors.lastname: Egía Zurutuza
authors.affiliation: Servicio de Farmacia, Hospital Universitario Donostia, San Sebastián (Guipúzcoa), España.
authors.forename: M B
authors.initials: MB
authors.lastname: Irastorza Larburu
authors.affiliation: Servicio de Farmacia, Hospital Universitario Donostia, San Sebastián (Guipúzcoa), España.
authors.forename: M P
authors.initials: MP
authors.lastname: Bachiller Cacho
mesh_terms: D000068438:Brimonidine Tartrate / Q000032:analysis; D002021:Buffers; D016568:Drugs, Generic / Q000737:chemistry; D005901:Glaucoma / Q000188:drug therapy*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D000077338:Latanoprost; D009883:Ophthalmic Solutions / Q000737:chemistry*; D010710:Phosphates / Q000032:analysis*; D011310:Preservatives, Pharmaceutical / Q000032:analysis; D011461:Prostaglandins F, Synthetic / Q000032:analysis; D013030:Spain; D013056:Spectrophotometry, Ultraviolet; D013999:Timolol / Q000032:analysis
chemical_list: D002021:Buffers; D016568:Drugs, Generic; D009883:Ophthalmic Solutions; D010710:Phosphates; D011310:Preservatives, Pharmaceutical; D011461:Prostaglandins F, Synthetic; D000068438:Brimonidine Tartrate; D000077338:Latanoprost; D013999:Timolol
keywords: Absorption spectrophotometry; Antiglaucomatoso; Colirio; Espectrofotometría de absorción; Eye drop; Fosfatos; Glaucoma medication; Phosphate; pH