Treatment of Acanthamoeba keratitis

The treatment of Acanthamoeba keratitis has now been possible since the first successful therapy developed in the mid 1980s with a combination of propamidine 0.1% (Brolene) and neomycin 1%. However, only half the patients responded to this regimen as the cysts were often resistant to neomycin and relatively insensitive to propamidine. This led to research for better therapy, culminating in the mid 1990s with research in Glasgow demonstrating much increased effectiveness with use of the biguanide chlorhexidine 0.02% and in London and Bristol for similar effectiveness with the polymeric polyhexamethylene biguanide (PHMB) 0.02%. Both biguanides were combined with propamidine for enhanced effectiveness but were also shown to be effective as monotherapy. While this therapy inactivates the trophozoites and cysts in Acanthamoeba keratitis in the majority of patients (approximately 90%), there have been notable failures particularly when presentation is late with deep stromal infection. Additional highly acanthamoebicidal drugs are needed that can penetrate the stroma for synergistic action. This role may be taken up by certain antineoplastic drugs, such as alkylphosphocholine-1 (Miltefosine), that also have antiprotozoal activity.