Asthmatic Cat? Don’t Use Nebulized NAC

N-acetylcysteine (NAC) is a mucolytic agent with antioxidant properties. In this study (a follow-up to a pilot study that found no adverse effects when NAC was administered to 25 healthy and 2 asthmatic cats), 6 cats with experimentally induced asthma were anesthetized, then pre- and posttreatment airway resistance and inspiratory plateau pressure measurements were obtained after aerosol delivery of NAC via endotracheal tube (400 mg cumulative dose). Results showed significantly increased airway resistance when cats received NAC as compared with saline; there was no significant difference in inspiratory plateau pressure measurements. All the cats exhibited at least one adverse reaction to the NAC aerosol: excessive airway secretions (n = 3), spontaneous cough (n = 2), unilateral strabismus during recovery (n = 1), and death (n = 1). The cat with the most severe asthmatic phenotype died during anesthetic recovery. Necropsy did not show a definitive cause of death; however, moderate-to-severe pulmonary changes consistent with asthma were found. None of the cats reacted adversely to the saline control. The authors acknowledge that the dose of NAC used in this study comes from human pediatrics, as pharmacokinetics for this drug has not been studied in the cat. It is not clear whether a different dose, as well as pretreatment with an aerosolized bronchodilator (as is customary in human patients), would have lowered the incidence of adverse events.

Commentary: The importance of a good clinical model when evaluating a drug that, in theory, should be helpful in managing feline asthma is demonstrated here. NAC increases airway reactivity and adverse reactions in cats with experimental asthma. Adverse effects of NAC were not noted in a previous study of cats, most without asthma. Since mucus is predominantly water, keeping the airways hydrated via systemic hydration will promote mucus clearance; and because the underlying trigger for mucus overproduction is inflammation, antiinflammatory medication coupled with bronchodilation remains the mainstay of airway disease management. Based on the results of this study, nebulization with NAC should not be considered in an asthmatic cat.—Rosie Henik, DVM, DACVIM

Endotracheal nebulization of N-acetylcysteine increases airway resistance in cats with experimental asthma. Reinero CR, Lee-Fowler TM, Dodam JR, et al. J FELINE MED SURG 13:69-73, 2011.