Purpose: Polyhexamethylene biguanide (PHMB) is a polymeric biguanide disinfectant that has been used previously in the treatment of Acanthamoeba keratitis. The authors report the first case of Nocardia asteroides keratitis treated successfully with PHMB. Further studies documenting the efficacy of PHMB against N. asteroides in vitro also are presented.
Methods: A soft contact lens wearer presented with an infectious keratitis. Cultures from the cornea grew N. asteroides. The infection resolved with the treatment with PHMB 0.02%. Serial dilutions of PHMB were performed against N. asteroides in culture.
Results: In vitro dilution studies determined that the minimal inhibitory concentration for PHMB against the tested isolate of N. asteroides was 0.01%. This is a concentration that has been shown to be well tolerated by the cornea in vivo.
Conclusions: Polyhexamethylene biguanide is effective against both Acanthamoeba and Nocardia and may have a wider range of usefulness than that currently recognized. Further testing, both in vitro and in vivo, is required.