Scintigraphic Assessment of Deposition of Radiolabeled Fluticasone Delivered from a Nebulizer and Metered Dose Inhaler in 10 Healthy Dogs

BACKGROUND: Aerosolized medications are increasingly being used to treat respiratory diseases in dogs. No previous studies assessing respiratory tract deposition of radiolabeled aerosols have been performed in conscious dogs. HYPOTHESIS/OBJECTIVES: Assess respiratory tract deposition of radiolabeled, inhalant corticosteroid (fluticasone propionate labeled with 99m Tc) delivered from a nebulizer and metered dose inhaler (MDI) to healthy dogs. ANIMALS: Ten healthy Foxhounds. METHODS: Prospective, randomized, cross-over pilot study. Initial inhalation method (nebulizer or MDI) was randomly assigned. Treatments were crossed over after a 7-day washout period. Treatments initially were performed using sedation. Dogs were imaged using 2-dimensional planar scintigraphy, with respiratory tract deposition quantified by manual region-of-interest analysis. Deposition calculated as percentage of delivered dose. Six of 10 dogs were randomly selected and reassessed without sedation. RESULTS: Inhalation method had significant effect on respiratory tract deposition (P = 0.027). Higher deposition was achieved by nebulization with mean deposition of 4.2% (standard deviation [SD], 1.4%; range, 1.9-6.1%); whereas MDI treatment achieved a mean of 2.3% (SD, 1.4%; range, 0.2-4.2%). Nebulization achieved higher respiratory tract deposition than MDI in 7 of 10 dogs. No statistical difference (P = 0.68) was found between mean respiratory tract deposition achieved in dogs when unsedated (3.8%; SD, 1.5%) or sedated (3.6%; SD, 1.7%). CONCLUSIONS AND CLINICAL IMPORTANCE: Study confirms respiratory tract deposition of inhalant medications delivered from a nebulizer and MDI in healthy dogs, breathing tidally with and without sedation. Respiratory tract deposition in these dogs was low compared to reported deposition in adult humans, but similar to reported deposition in children