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Local and systemic effects of intralaryngeal injection of cidofovir in a canine model

Objective: The safety of intralaryngeal injection of cidofovir remains a concern. Our goal was to evaluate local and systemic effects of intralaryngeal injection of cidofovir. Study Design: Animal study using a canine model. Methods: Two groups of three young beagle dogs (6 vocal folds in each group) were used. Subepithelial vocal fold injections were performed in each group biweekly for 6 months with 0, 2.5, 5, 10, 20, and 37.5 mg cidofovir in a 0.5 mL volume. Direct laryngoscopy was performed at each injection interval. Complete blood cell count and renal parameters were measured at baseline and monthly thereafter. Histopathologic examination of the vocal folds was performed after the 6‐month injection period in one group of animals and after an additional 6‐month observation period in the second group. Results: Endomysial edema with muscle fiber separation and dose‐dependent atrophy and scarring of the vocal folds was present. Onset of atrophy and scarring was observed after 3,7, and 11 injections in the vocal folds injected with 37.5, 20, and 10 mg cidofovir, respectively. After the 6‐month observation period, recovery of histologic abnormalities was complete in the low‐dose (0, 2.5 mg) vocal folds, near complete in the intermediate‐dose (5, 10 mg) vocal folds, and no apparent recovery was seen in the high‐dose (20, 37.5 mg) vocal folds. Leukocyte count and renal parameters remained unchanged at up to 4.26 mg/kg body weight of systemic dose of cidofovir. Conclusions: Intralaryngeal cidofovir leads to dose‐dependent scarification of the vocal folds that appears irreversible at higher doses. Lower concentrations of this drug should be used in intralesional intralaryngeal use.