Adjunctive povidone-iodine for <i>Acanthamoeba</i> keratitis: a randomized trial

The aim of this study was to determine the antiamoebic efficacy of povidone-iodine when used as an adjunct to topical biguanide therapy for <i>Acanthamoeba</i> keratitis. Patients with smear- or culture-positive <i>Acanthamoeba</i> keratitis received topical chlorhexidine 0.04%, half-hourly for 2 days, then hourly for days 3-6, then eight times per day for days 7-28. Participants were randomized in a 1:1 ratio to receive either adjunctive topical povidone-iodine at the same frequency as chlorhexidine or no additional therapy (i.e., control group). Povidone-iodine was initially administered as a 2.5% solution but was reduced to a 1% solution after several reports of intolerance. The primary outcome was <i>Acanthamoeba</i> growth from the culture of corneal scrapings at 1, 2, and 4 weeks after randomization, as assessed by laboratory staff masked to treatment allocation. Of 49 patients enrolled, 25 were randomized to adjunctive povidone-iodine (mean age 48 [SD 16] years; 32% female) and 24 to control (mean age 43 [15] years; 33% female). Four (16%) participants discontinued 2.5% povidone-iodine prematurely due to intolerance. The proportion of participants with a positive culture during the initial 4 weeks of antiamoebic treatment was not significantly different in the povidone-iodine group (6/18 [33%] at 4 weeks) and control group (5/16 [31%] at 4 weeks) (RR 0.90, 95%CI: 0.35-2.29; <i>P</i> = 0.82). When used as an adjunctive to standard biguanide therapy, povidone-iodine did not markedly accelerate the clearance of <i>Acanthamoeba</i> organisms from the corneal surface over the initial month of therapy.This study is registered with ClinicalTrials.gov as NCT03484507.