A patient using contact lenses developed corneal infection. On investigation diagnosis of acanthomoeba keratitis is made. Which of the following is the drug of choice?

Acanthamoeba infection is an impoant cause of keratitis in contact lens wearers. Diagnosis is facilitated by confocal microscopy. Treatment is hampered by the organism's ability to encyst within the corneal stroma. Topical biguanides are probably the only effective primary treatment. Rx: Medical treatment is usually staed with intensive topical propamidine isethionate (1% solution) and either polyhexamethylene biguanide (0.01%-0.02% solution) or foified neomycin eyedrops Polyhexamethylene biguanide is considered first line agent in the treatment of acanthamoeba. It is available as a contact lens disinfectant at a low concentration and as a swimming pool supplement at high concentration. This drug interferes with cytoplasmic membrane integrity and inhibit essential respiratory enzymes of multiple microbes. Other treatment options includes use of : Aromatic diamidines such as propamidine isethionate, brolene and pentamidine, neomycin and paramomycin, imidazoles and triazole antifungals and polymixins. Ref: Ocular Therapeutics Handbook: A Clinical Manual By Bruce E. Onofrey, 2nd Edition, Page 232; Biswell R. (2011). Chapter 6. Cornea. In P. Riordan-Eva, E.T. Cunningham, Jr. (Eds), Vaughan & Asbury's General Ophthalmology, 18e.