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Editors Selection IGR 10-3

Medical Therapy: Preserved versus preservative free prostaglandin

Comment by Malik Kahook on:

26276 Switching from a preserved to a preservative-free prostaglandin preparation in topical glaucoma medication, Uusitalo H; Chen E; Pfeiffer N et al., Acta Ophthalmologica, 2010; 88: 329-336

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There has been a great deal of debate surrounding the nature and relevance of the in-vitro and in-vivo effects of benzalkonium chloride (BAC) on human ocular surface cells. Most in-vitro studies of BAC, whether or not coupled with active ingredients, show a clear toxic response at various concentrations.^1,2 Recent clinical studies addressing this issue have focused on prostaglandin analogues (PGAs) preserved with BAC or alternative agents like Sofzia and have resulted in contradictory conclusions.^3,4 Uusitalo et al. (908) recently reported the results of a study involving patients previously treated with latanoprost (preserved with 0.02% BAC) who were then switched to preservative free tafluprost. All enrolled patients had at least two ocular symptoms or one sign and one symptom during their treatment with latanoprost. After 12 weeks of tafluprost therapy, a significant number of patients reported improved symptoms (irritation, stinging, burning, etc.) and experienced improvement in tear break-up time (4.5 ± 2.5 seconds to 7.8 ± 4.9 seconds; p < 0.001), conjunctival hyperemia, blepharitis and corneal/ conjunctival staining. Moreover, there was a significant reduction in the proportion of patients with abnormal conjunctival cells based on expression of HLA-DR and MUC5AC on flow cytometry from impression cytology specimens before and after the switch. To better understand the findings of Uusitalo et al., it would be helpful to briefly review the findings of two recent studies. Whitson and colleagues examined ocular surface signs and symptoms in a cohort of patients initially taking latanoprost (preserved with BAK 0.02%) who were then randomized into one of three groups: (a) continuation of latanoprost monotherapy, (b) bimatoprost with 0.005% BAC or, (c) travoprost with SofZia.⁴ They found no significant differences among the treatment groups in conjunctival hyperemia, corneal staining, or tear break-up time at the latanoprost-treated baseline or at any follow-up visit for the duration of the three month study. Enrolled patients had near normal tear break-up times at enrollment and were not required to have any intolerance to latanoprost prior to enrollment. Horsley and Kahook reported an eight-week study in which patients were switched from latanoprost with 0.02% BAC to travoprost with SofZia. The study found an improvement in tear break-up time (2.02 ± 0.71 to 6.34 ± 1.31 seconds; p < 0.001) as well as improvement in inferior corneal staining (2.40 ± 0.87 to 1.38 ± 0.59; p < 0.001).³ Of note, all patients in the study had low tear break-up time and significant corneal staining at enrollment. These two studies clearly illustrate what I believe to be an important takehome message of the study performed by Uusitalo and colleagues. Patients who are tolerant of their latanoprost monotherapy and who do not show signs of ocular surface disease are not likely to experience any measurable improvement during a 12-week study in which they are switched to other medications. On the other hand, patients who are selectively chosen for enrollment based on their intolerance of latanoprost (based on signs and/or symptoms) are more likely to show measurable improvement after switching therapy and completing 8-12 weeks of follow up. Uusitalo et al. should be commended for adding conjunctival impression cytology to their study as this helps to solidify the validity of the other metrics measured in their study while providing objective data. However, future studies should employ a cross-over design in order to better understand which in vivo changes, if any, are truly caused by topical therapeutics and/ or their preservatives.

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