The Orphan Drug for Acanthamoeba Keratitis (ODAK) Trial: PHMB 0.08% (Polihexanide) and Placebo versus PHMB 0.02% and Propamidine 0.1%

Abstract

ObjectivesTo compare topical PHMB (polihexanide) 0.02% (0.2 mg/ml) + propamidine 0.1% (1 mg/ml) [PHMB 0.02%+propamidine] to PHMB 0.08% (0.8 mg/ml) with placebo [PHMB 0.08%] for Acanthamoeba keratitis (AK) treatment. DesignProspective randomized, double-masked, active-controlled, multicentre, Phase3 study (ClinicalTrials.gov NCT03274895). Participants135 at six European centres between 08/17/2017 to 06/18/2021. MethodsPrincipal inclusion criteria: ≥12 years old; in vivo confocal microscopy (IVCM) with clinical findings consistent with AK. Also included were participants with concurrent bacterial keratitis, using topical steroids, antiviral and antifungal drugs before randomisation. Principal exclusions: concurrent herpes or fungal keratitis, use of anti-amoebic therapy (AAT). Randomisation: 1:1 computer-generated, block size 4. This was a superiority trial having a predefined non-inferiority margin. The sample size of 130 participants gave approximately 80% power to detect 20 percentage point superiority for PHMB 0.08% for the primary outcome of the medical cure rate (without surgery or change of AAT) within 12 months (MCR_12), cure defined by clinical criteria 90 days after discontinuing anti-inflammatories and AAT. A prespecified multivariable analysis adjusted for baseline imbalances in risk factors affecting outcomes. Main outcome measuresThe MCR_12. Secondary outcomes included best-corrected visual acuity (BCVA) and treatment failure rates. Safety outcomes included adverse event rates. Results135 participants were randomised providing 127 in the full analysis subset (61 on PHMB 0.02%+propamidine and 66 on PHMB 0.08%) and 134 in the safety analysis subset. The adjusted MCR_12 was 86.6% (unadjusted 88.5%) for PHMB 0.02%+propamidine and 86.7% (unadjusted 84.9%) for PHMB 0.08%; the non-inferiority requirement for PHMB 0.08% was met (adjusted difference 0.1 percentage points, lower one-sided 95% confidence limit -8.3 percentage points). Secondary outcomes were similar for both treatments and not analysed statistically: median BCVA of 20/20, an overall treatment failure rate of 17/127 (13.4%) of whom 8/127 (6.3%) required therapeutic keratoplasty. There were no serious drug related adverse events. ConclusionsPHMB 0.08% monotherapy may be as effective (or at worse only eight percentage points less effective) as dual therapy with PHMB 0.02%+propamidine (a widely used therapy) with medical cure rates of >86%, when used with the Trial treatment delivery protocol, in AK populations with similar disease severity.