Purpose: A case of acyclovir-resistant herpes simplex virus keratouveitis after penetrating keratoplasty is reported. Methods: Resistance to acyclovir was evident clinically and was confirmed by in vitro susceptibility testing. The susceptibility of the herpes simplex isolates to acyclovir and foscarnet was determined by a dye uptake assay that measured cytopathic effect, and thymidine kinase activity was measured by a plaque autoradiography technique. Results: The viral isolate from postoperative day 22 was susceptible to acyclovir and foscarnet, and showed normal thymidine kinase activity. Isolates from postoperative days 29 and 32 (coinciding with deterioration in clinical appearance) were resistant to acyclovir, susceptible to foscarnet, and deficient in thymidine kinase activity. Conclusion: Practitioners should be aware of the potential for the emergence of resistance in this setting; prophylaxis and rational alternate therapies are discussed.
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