Effect of low dose azithromycin on the fecal microbiome and fecal bile acids in healthy dogs.

Authors

Colin Smith, Roman Husnik, Frederic Gaschen, Claudia Kirk, Xiaojuan Zhu, Jan Suchodolski

Published in

Journal of veterinary internal medicine. Volume 40. Issue 5. Sep 01, 2026.

Abstract

Azithromycin has prokinetic effects at low doses in people, cats, and anecdotally, in dogs; however, antibiotics alter the fecal microbiome and metabolome.
To prospectively evaluate the effects of low-dose azithromycin, hypothesizing that it would alter the fecal microbiome and fecal bile acids in healthy dogs.
Eleven healthy research dogs.
Prospective study. Dogs received azithromycin (2 mg/kg PO q8h) for 8 days. Fecal samples were collected before (day 1), during (day 6), and after azithromycin administration (days 11, 26, 36, 45). Fecal consistency was assessed daily. Microbiome analysis included qPCR quantification of 16 core bacterial taxa and the Dysbiosis Index. Fecal concentrations of conjugated and unconjugated bile acids (UBAs) were measured on days 1, 11, and 45.
Fecal scores increased during azithromycin administration (P = .009). Abundance of 7 of 16 taxa decreased significantly on day 6, including Peptacetobacter hiranonis (P. hiranonis; P < .001), Faecalibacterium (P < .001), and Fusobacterium (P = .031). Abundance of Streptococcus significantly decreased on day 11 (P = .003). Percentage of primary UBAs increased (P = .017; median, 94.06%; range, 0.73%-96.08%), returned to baseline by day 45, and negatively correlated with abundance of P. hiranonis (r = -0.936 [95% CI, -0.973, -0.852], P < .001). Abundance of 8 of 9 significantly altered taxa recovered, with abundance of Streptococcus remaining decreased.
Low-dose azithromycin induces a mostly reversible dysbiosis and reversible decrease in secondary fecal UBAs. Atypical decreases in Streptococcus abundance can also occur.

PMID:
42801332
Bibliographic data and abstract were imported from PubMed on 27 Sep 2026.

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