**7. Treatment options in AK**

## **7.1. Factors complicating effective pharmacotherapy in AK**

AK treatment is difficult and often unsuccessful despite of advances in pharmacotherapy. There are several factors that are listed as influencing difficulties and still not fully effective of applied therapy [12,18].

AK is often incorrect diagnosed due to nonspecific clinical symptoms; similar clinical pictures to this observed in the amoebic keratitis may give a wide range of agents e.g. viral *Herpes simplex*, bacterial -mostly *Pseudomonas aeruginosa* or fungi of *Fusarium* spp.

Additionally, mixed amoebic, fungal viral and bacterial keratitis may occur that complicate therapeutic management.

*Acanthamoeba* strains vary in their pathogenicity: they may be virulent, weakly virulent or nonvirulent; they show different susceptibilities to chemicals and answer to pharmacotherapy.

It is also underlined that extremely high resistance of *Acanthamoeba* cysts to different chemicals, disinfectants as well as anti-microbial and anti-parasitic drugs result in disappointing thera‐ peutic management [12,18,54,59-64].

Among the abovementioned facts, diagnostic mistakes that cause delayed in a beginning of an efficient treatment may result in a prolonged, severe course of AK and vision deterioration.

It is also emphasized that some chemicals can induce amoebic encystment that subsequently, by excystment, may lead to repeated development of trophozoites, thus an activation of the dormant cysts can lead to recurrence of the disease. It is why not only amoebicidal effects but also the cysticidal efficacy of applied therapeutics is very important [43-46].

In some research works, also in our experimental studies it has been reported that higher concentrations of drugs and some new-synthesized imidazole derivatives may be *in vitro* efficacious against *Acanthamoeba* strains and result not only in amoebostatic but also in amoebicidal effects. However, many of these chemicals cannot be applied *in vivo* in such concentrations due to their toxicity for human tissues [44-50].

#### **7.2. Treatment recommended in management in AK**

modified enriched culture medium containing antibiotics (penicillin, streptomycin) is useful

Simultaneously, molecular methods of classification of *Acanthamoeba* isolates, with the use of sensitive PCR techniques, basing on genotype associations are distinguishing for diagnostics and for the characterization of clinical and environmental *Acanthamoeba* isolate [12,18,27,32,33,59]. In this modern approach, the species identification is based on the combi‐ nation of morphological and molecular characteristics of amoebae. Additionally, our experi‐ ences gave convincing evidences of an importance of a clinical examination of the affected eyes and laboratory differentiations/identification of amoebic forms in material deriving from

AK treatment is difficult and often unsuccessful despite of advances in pharmacotherapy. There are several factors that are listed as influencing difficulties and still not fully effective of

AK is often incorrect diagnosed due to nonspecific clinical symptoms; similar clinical pictures to this observed in the amoebic keratitis may give a wide range of agents e.g. viral *Herpes*

Additionally, mixed amoebic, fungal viral and bacterial keratitis may occur that complicate

*Acanthamoeba* strains vary in their pathogenicity: they may be virulent, weakly virulent or nonvirulent; they show different susceptibilities to chemicals and answer to pharmacotherapy. It is also underlined that extremely high resistance of *Acanthamoeba* cysts to different chemicals, disinfectants as well as anti-microbial and anti-parasitic drugs result in disappointing thera‐

Among the abovementioned facts, diagnostic mistakes that cause delayed in a beginning of an efficient treatment may result in a prolonged, severe course of AK and vision deterioration. It is also emphasized that some chemicals can induce amoebic encystment that subsequently, by excystment, may lead to repeated development of trophozoites, thus an activation of the dormant cysts can lead to recurrence of the disease. It is why not only amoebicidal effects but

In some research works, also in our experimental studies it has been reported that higher concentrations of drugs and some new-synthesized imidazole derivatives may be *in vitro* efficacious against *Acanthamoeba* strains and result not only in amoebostatic but also in amoebicidal effects. However, many of these chemicals cannot be applied *in vivo* in such

*simplex*, bacterial -mostly *Pseudomonas aeruginosa* or fungi of *Fusarium* spp.

also the cysticidal efficacy of applied therapeutics is very important [43-46].

concentrations due to their toxicity for human tissues [44-50].

for classification cysts to the morphological level.

**7.1. Factors complicating effective pharmacotherapy in AK**

infected corneas.

110 Advances in Common Eye Infections

**7. Treatment options in AK**

applied therapy [12,18].

therapeutic management.

peutic management [12,18,54,59-64].

Currently, there are not known single-treatment methods effective against both trophozoites and cysts of *Acanthamoeba*; generally, AK is difficult to treat. *Acanthamoeba* stages differ in their susceptibility to various drugs. Trophozoite form is highly responsive to the treatment, while cysts are highly resistant as the cystic form protects the amoebic organism from unfavorable environmental factors, including drugs. The therapeutic approach recommended in AK consists of antimicrobial agent's combination [4,12,18,36].

The mainstay agents that are used as a first-line treatment for *Acanthamoeba* keratitis are diamidines (propamidine, hexamidine) and biguanides (polyhexamethylene biguanide (– PHMB), chlorhexidine), which were found to be cysticidal anti-amoebics *in vitro*. PHMB is the most preferred agent in monotherapy or in combinations with other drugs. Chlorhexidine can also be used in monotherapy, but it is much more effective in combined treatment. Propami‐ dine is used in combination with one of biguanides, as the latter are more effective against cysts of *Acanthamoeba* [65]. Although neomycin was used widely, it is ineffective against cysts *in vitro*; thus, it is no longer used by most ophthalmologists.

However, particularly after earlier improper treatment in other centers, the combination drug therapy with the antimicrobial agents is used more or less successfully. Additionally, such factors as human organism status, a virulence of amoeba strains, phase of infection, and kind and concentration of the chemicals applied may determine variability in effects of drugs on trophozoites and cysts of several *Acanthamoeba* strains [12,16,22,45,50,64-67].

The most frequently used agents that achieve sufficient high concentrations at the site of infection and are effective against trophozoites and cysts of *Acanthamoeba* are cationic disin‐ fectants: chlorhexidine 0.02–0.2% (200–2000 g/ml), polyhexamethylene biguanide (PHMB) 0.02–0.06% (200–600g/ml), and propamidine isethionate (Brolene 0.1%). These topical antimi‐ crobials should be administered immediately to the infected eye one to two drops on the surface of the cornea at the first several days, every hour, minimum nine times/day, and, next, every 3h. The therapy duration is depending on clinical response. The amoebae may persist in the encysted stage for months and reactivate after therapy discontinuation. It was indicated in many earlier and current studies that a therapy continuation is very important to avoid an activation of the dormant cysts that may lead to repeated trophozoite development and thus to recurrence of the disease [4,12,13]. Some authors advise the treatment for 3- 4 months in order to preclude recurrence; however, the treatment for 6–12 months is also recommended. Nevertheless, it is reported that *Acanthamoeba* strains/cysts resistance to drug may occur, which is the main difficulty in AK treating [12,18,43,63,66]; particularly, resistance to propamidine and, also toxicity effect are observed in the course of AK. Corneal epithelial toxicity has been minimal for both chlorhexidine 0.02% and PHMB 0.02%. The greatest frequency of ocular toxicity has been reported with propamidine; the most common side effect is the superficial punctate keratopathy [65]. Pain can be relieved by topical cycloplegics (e.g. atropine 0.5-1.0%, scopolamine 0.25% t.i.d.), agents and oral non-steroidal anti-inflammatory medications (e.g. naproxen 250-500mg p.o. b.i.d.).

It should be also taken into consideration that co-infections with other microorganisms may complicate the course and treatment of the severe amoebic disease [18,49-51].

Although the low doses of topical steroids can be useful to diminish inflammation in cases of controlled infection but the use of topical corticosteroids is controversial.

Systemic corticosteroids are preferred over topical ones in cases of severe inflammation. This route of administration provides better ocular safety profile (less concentration in the cornea) but less body safety profile. However there are some suggestions that steroid use may result in increased pathogenicity of the amoebae [68].

If the topical pharmacotherapy fails, surgical interventions are needed [12,44,64,67]. Crosslinking and cryopreserved amniotic membrane graft (AMG) have been reported to be effective in AK.

The corneal transplantation can be performed for therapeutic or optical indications. Thera‐ peutic, usually penetrating, keratoplasty is applied when the infectious process spreads to the corneal stroma, causing corneal melting and thinning despite of aggressive prolonged antiamoebic therapy [4,12,18]. In a case of threatening or completed perforation of the cornea, the surgery must be performed urgently. Some authors recommend systemic steroids prior to surgery if concomitant limbitis or scleritis is present [69].

Sacher et al.[70] show that pretreatment of *Acanthamoeba* keratitis with intravenous pentami‐ dine before therapeutic keratoplasty may assist with the achievement of microbiological cure, clear graft, and good visual outcome in a majority of eyes with AK.

The size of corneal graft should be minimum to excise an inflamed and necrotic tissue. Although remaining clinically healthy cornea is frequently also infected, this tissue should be saved because of the higher risk of rejection with large/decentrated grafts and because the possibility of repeat grafting should be kept in mind in the event of recurrence; a further graft represents a new food source for the organism and can be used to attract residual amoebae [69].

In a case of therapeutic keratoplasty for AK, the topical steroids in combination with antiamoebic drugs are applied for 6-12 months following keratoplasty, to relieve pain, lessen the inflammation, and prevent graft rejection and recurrence of infection. Corneal grafts per‐ formed in the eyes with active inflammation are the high-risk transplants and they required systemic immunosuppression similar to this given in organ transplants (cyclosporine and/or mycophenolate mofetil). Apart from a poor graft survival, the postoperative glaucoma is a frequent complication.

In optical keratoplasty performed after resolution of active keratitis there is an excellent prognosis for both graft survival and visual outcome [71].

Promising clinical results were reported from amoebicidal effect of combined riboflavin and UV-A (ultraviolet light A, 365nm wavelength) exposure -corneal cross-linking (CXL) that was used for stabilization of corneal melting which can delay surgical treatment [12,72,73]. CXL has also an antimicrobial effect that is due to the effect of UV light interacting with riboflavin as the chromophore. It damages both the DNA and RNA of pathogens. Photoactivated chromophore for infectious keratitis (PACK)-CXL is an alternative to standard antibiotic therapy in treating infectious corneal disorders, and may help reduce the microbial resistance to antibiotics and avoid therapeutic keratoplasty in some cases [74].

Many chemicals and antimicrobials were examined and are still tested *in vitro* for their potential activity against different species, strains and isolates of *Acanthamoeba* [45,54,61-63,67]. Due to the toxicity of high concentrations of agents tested and a drug resistance, an optimal strategy for anti-acanthamoebic treatment is not yet defined. Further studies in this field are needed, particularly, in terms of cysticidal effects of the chemicals tested.
