Topical therapies will usually involve a Biguanide (polyhexamethylene biguanide (PHMB) 0.02% or chlorhexidine 0.02%) in combination with a diamidine (propamidine is ethanoate 0.1% or hexamidine 0.1%) initially at a high frequency. Hourly drops may be tapered down after 48 hours to alleviate the epithelial toxicity caused by both these compounds. Topical therapy for AK needs to be continued much longer than antibacterial therapy regimes due to the encystment of the amoebae, which is much harder for the drugs to penetrate. Typical regimes will taper over around 6 months.