Phosphate concentrations in antiglaucoma medication.
BACKGROUND
Eye drops may contain phosphates as part of their buffer system. In the presence of epithelial keratopathy a high concentration of phosphate favours corneal calcification. To date European legislation does not require a quantitative declaration of the phosphates since buffers are regarded as additives. The knowledge of the phosphate concentration in medications helps to prevent corneal calcifications. Our study gives an overview on the amount of phosphate contained in antiglaucoma drops.


METHODS
21 samples of commercially available antiglaucoma drops were tested. The quantification of phosphate was performed using the molybdate method on a Modular P autoanalyzer.


RESULTS
10 of 21 (47 %) glaucoma drops had a phosphate concentration above physiological levels (> 1.45 mmol/L). A concentration higher than 100 mmol/L was found in four preparations that contained timolol.


CONCLUSIONS
Many antiglaucoma drops contain unphysiological levels of phosphate, very high concentrations are found in some beta-blockers. These preparations have the potential to favour the formation of insoluble crystalline calcium phosphate deposits when used on a damaged corneal surface, and should therefore be avoided.
Bernauer
W
W
Department of Ophthalmology, University of Zürich, Zürich, Switzerland. wolfgang.bernauer@hin.ch
Thiel
M A
MA
Rentsch
K M
KM
D000316:Adrenergic alpha-Agonists / Q000737:chemistry* / Q000627:therapeutic use; D000319:Adrenergic beta-Antagonists / Q000737:chemistry* / Q000627:therapeutic use; D000959:Antihypertensive Agents / Q000737:chemistry* / Q000627:therapeutic use; D018678:Cholinergic Agents / Q000737:chemistry* / Q000627:therapeutic use; D004340:Drug Contamination / Q000517:prevention & control; D004353:Drug Evaluation, Preclinical / Q000379:methods; D005901:Glaucoma / Q000188:drug therapy; D006801:Humans; D009883:Ophthalmic Solutions / Q000737:chemistry*; D010710:Phosphates / Q000032:analysis*; D011453:Prostaglandins / Q000737:chemistry* / Q000627:therapeutic use
D000316:Adrenergic alpha-Agonists; D000319:Adrenergic beta-Antagonists; D000959:Antihypertensive Agents; D018678:Cholinergic Agents; D009883:Ophthalmic Solutions; D010710:Phosphates; D011453:Prostaglandins