A clinicopathologic study of in vitro sensitivity testing and Acanthamoeba keratitis

To examine the extent of any correlation between the in vitro sensitivity and the clinical outcomes of Acanthamoeba keratitis.

The clinical outcomes were correlated with the in vitro sensitivity of 23 isolates of 23 patients with culture-positive Acanthamoeba keratitis. The laboratory assay assessed the amoebicidal and cysticidal efficacy of 13 drugs.

Most agents were effective against the trophozoites in vivo. Polyhexamethylene biguanide (PHMB) and chlorhexidine were the most successful cysticidal agents, followed by sepazonium and propamidine. Clotrimazole, paramomycin, and ketoconazole were cysticidal in a few specimens, but usually in high concentrations. Neomycin was ineffective against cysts in vivo. Nineteen patients were treated with topical propamidine and neomycin, and a medical cure was obtained in nine (47%). There was poor correlation between the clinical outcomes of individual cases and the in vitro sensitivity testing. The medical failures were treated with topical PHMB and propamidine and eight of ten (80%) of these were medically cured. Two patients, however, were still culture positive after 28 and 41 weeks of treatment. PHMB has an excellent in vitro sensitivity profile, but the two cases of failure were sensitive to the drug and resistance had not developed.

In vitro sensitivity testing has been important in the screening of new agents, although disappointing in the management of individual cases in this set of studies.