PHMB monotherapy effective alternative to PHMB and propamidine combo for treatment of Acanthamoeba keratitis

Acanthamoeba keratitis (AK) is a rare but serious eye infection caused by a microscopic amoeba and typically requires complex treatments. A recent Phase 3 clinical trial has shown that PHMB 0.08% (0.8 mg/ml) alone may be as effective as dual therapy with PHMB 0.02% (0.2 mg/ml) + propamidine 0.1% (1 mg/ml) for treating Acanthamoeba keratitis (AK).

This study was published in Ophthalmology by John Dart and colleagues. This was a prospective, randomised, double-masked, active-controlled, multicenter Phase 3 study. The study involved 135 participants aged 12 or older with clinical findings consistent with AK. Some participants had concurrent bacterial keratitis and had used other eye medications before the study. Participants were randomly assigned to receive either PHMB 0.02% + propamidine or PHMB 0.08%. The primary outcome was the MCR_12, defined by clinical criteria 90 days after discontinuing anti-inflammatories and anti-amoebic therapy. A prespecified multivariable analysis was conducted to adjust for baseline imbalances in risk factors affecting outcomes. The primary outcome, MCR_12, was assessed for both treatment groups, and secondary outcomes included BCVA and treatment failure rates. Safety outcomes focused on adverse event rates.

Results:

• A total of 135 participants were randomized.
• The adjusted MCR_12 was 86.6% for PHMB 0.02% + propamidine and 86.7% for PHMB 0.08%.
• The non-inferiority requirement for PHMB 0.08% was met.
• Secondary outcomes, including median BCVA of 20/20 and treatment failure rates, were similar for both treatments.
• No serious drug-related adverse events were reported.

The study's primary outcome, the medical cure rate (MCR_12) within 12 months, demonstrated that both treatment groups had MCRs exceeding 86%, meeting the non-inferiority requirement for PHMB 0.08%. Secondary outcomes, including best-corrected visual acuity (BCVA) and treatment failure rates, were similar for both treatments. Importantly, no serious drug-related adverse events were reported.

This study suggests that PHMB 0.08% monotherapy may be a viable treatment option for AK, demonstrating effectiveness comparable to dual therapy. The findings provide hope for more straightforward and cost-effective treatments for this rare but challenging eye condition.

Reference:

Dart, J. K. G., Papa, V., Rama, P., Knutsson, K. A., Ahmad, S., Hau, S., Sanchez, S., Franch, A., Birattari, F., Leon, P., Fasolo, A., Kominek, E. M., Jadczyk-Sorek, K., Carley, F., Hossain, P., & Minassian, D. C. The Orphan Drug for Acanthamoeba Keratitis (ODAK) trial: PHMB (polihexanide) 0.08% and placebo versus PHMB 0.02% and propamidine 0.1%. Ophthalmology,2023. https://doi.org/10.1016/j.ophtha.2023.09.031