Faecal Microbiota Transplantation Reduces Lesion Severity and Medication Use in Canine Atopic Dermatitis: A Randomised, Placebo‐Controlled, Double‐Blinded Clinical Trial

BACKGROUND: Faecal microbiota transplantation (FMT) is an established therapy for gastrointestinal disease, yet its role in canine atopic dermatitis (cAD) remains unclear. HYPOTHESIS/OBJECTIVES: We hypothesised that adjunctive FMT improves clinical severity and reduces symptomatic medication use in dogs with cAD. The objective was to evaluate efficacy and safety versus placebo. ANIMALS: Forty-six client-owned dogs with naturally occurring cAD were enrolled from a referral hospital population; 40 completed the study (FMT n = 20, placebo n = 20). MATERIALS AND METHODS: Prospective, randomised, placebo-controlled, double-blinded clinical trial. Dogs received daily oral lyophilised FMT capsules for 90 days plus three monthly rectal FMT administrations (Day [D]0, D30, D60) or placebo capsules with sham handling. Concomitant symptomatic therapies were permitted. Outcomes included Canine Atopic Dermatitis Extent and Severity Index, fourth iteration (CADESI-04), pruritus Visual Analog Scale (PVAS), Medication Score (D0-90) and Owner Global Assessment of Treatment Efficacy (OGATE, D90). RESULTS: CADESI-04 scores were lower with FMT at month (M) 2 (7 ± 6 vs. 16 ± 12; p = 0.006) and month 3 (8 ± 6 vs. 15 ± 12; p = 0.020). Sustained responders (≥ 50% CADESI-04 improvement at M2 and M3) were more frequent with FMT (35% vs. 5%; p = 0.044). In the FMT group, the medication scores were lower at M2 (16 ± 10 vs. 23 ± 11; p = 0.033) and M3 (13 ± 10 vs. 24 ± 15; p = 0.007) compared to placebo. PVAS decreased in both groups without between-group differences. OGATE favoured FMT (p = 0.028). FMT was well tolerated. CONCLUSIONS AND CLINICAL RELEVANCE: Adjunctive FMT reduced lesion severity and medication requirements, supporting its use as a safe microbiome-based add-on therapy in cAD.