Do probiotics help a dog on antibiotics?
Antibiotics upset most dogs’ guts. The trials of probiotics given alongside them: what a synbiotic did for appetite and diarrhea, what a live yeast did, and what did not work.
Quick answer
Modestly, and the microbiome takes months to recover either way. In 22 dogs given enrofloxacin and metronidazole, every dog developed diarrhea and most went off food; a synbiotic (Proviable-Forte plus Mycequin, a S. boulardii product) kept food intake closer to normal (P=.04) but did not prevent the diarrhea, and neither group’s microbiome had recovered by day 84. Adding FortiFlora to metronidazole in shelter dogs raised the share of days with normal stools. Lactobacillus rhamnosus GG did not prevent relapse in tylosin-responsive dogs.
The dog trials
The clearest study gave 22 healthy dogs a week of enrofloxacin at 10 mg/kg and metronidazole at 12.5 mg/kg with either a synbiotic (Proviable-Forte at 1×1010 CFU plus Mycequin, Saccharomyces boulardii at 1×1010 CFU) or placebo. In the first period, 41% went off food, 77% vomited and 100% developed diarrhea; the synbiotic made the food-intake derangement smaller (P=.04) but did not stop the diarrhea (Whittemore et al., 2019). When the same dogs were re-examined, the microbiome had not recovered in either group by days 82 to 84 (Whittemore et al., 2021).
In shelter dogs with diarrhea treated with metronidazole, adding FortiFlora for seven days raised the share of days with normal stools from 46.9% to 65.6% (P=.0496), though the share normal by day 7 was not significantly different (Fenimore et al., 2017). A live yeast, Saccharomyces cerevisiae (Actisaf), given to 20 dogs for 31 days around a metronidazole course lowered TNF-alpha (p=0.002), and the dysbiosis resolved in both groups by day 24 (Arghavani et al., 2025).
One negative result belongs in the list: Lactobacillus rhamnosus GG, the Culturelle strain that has the human antibiotic-diarrhea evidence, did not prevent diarrhea relapse in any of nine tylosin-responsive dogs (Westermarck et al., 2005). Human results do not transfer.
What the cat trials add
Cats have two placebo-controlled results in the same setting. In 27 cats on amoxicillin-clavulanate, FortiFlora lowered the diarrhea scores over days 1 to 11 (P=0.0058) (Torres-Henderson et al., 2017) and normalized the dysbiosis index by day 14 (Slaughter et al., 2026). In 16 cats on clindamycin, all finished the course on Proviable-DC against half on placebo (P=0.04) (Stokes et al., 2017).
How to use one
The trials started the probiotic with the antibiotic and continued for one to three weeks after. Labels for the live products say to give them a few hours apart from the antibiotic dose; S. boulardii is a yeast and is not killed by antibacterial drugs, which is the case for using it during the course. None of this replaces finishing the antibiotic as prescribed, and diarrhea with blood, vomiting more than twice a day or a dog that is off water is a call to the vet, not a supplement question.
Products in this catalog with the trials above
- Nutramax Proviable-DC capsules — dogs and cats, $0.56 a day
- Purina Pro Plan Veterinary Supplements FortiFlora Canine — dogs, $1.03 a day
- AnimalBiome S. boulardii + FOS Powder for Cats and Dogs — dogs and cats, $0.89 to $4.45 a day by weight
- Full Bucket Daily Dog Probiotic — dogs, $0.51 to $1.03 a day by weight
Common questions
Should I give my dog a probiotic while on antibiotics?
The trials give modest support: a synbiotic kept food intake closer to normal in 22 dogs on enrofloxacin and metronidazole without preventing diarrhea, and FortiFlora added to metronidazole raised the share of days with normal stools in shelter dogs. Give a live product a few hours apart from the antibiotic; S. boulardii, a yeast, can be given with it.
Which probiotic is best for a dog on antibiotics?
The one tested in that setting: the Proviable-Forte plus S. boulardii combination (22 dogs) and FortiFlora alongside metronidazole (shelter dogs). Lactobacillus rhamnosus GG, the human antibiotic-diarrhea strain, did not prevent relapse in tylosin-responsive dogs.
How long after antibiotics should a dog take probiotics?
The trials continued for one to three weeks after the course. The microbiome itself had not recovered by day 84 in either group in the 22-dog study, so a few weeks is what the evidence covers, not months.
Does S. boulardii help dogs on antibiotics?
As part of a synbiotic with Proviable-Forte it reduced the food-intake derangement in 22 dogs on enrofloxacin and metronidazole; on its own it has a 60-day placebo-controlled trial in 20 dogs with chronic enteropathy showing better stool frequency and consistency, not an antibiotic trial.
Sources
- Whittemore JC, et al. Effects of a synbiotic on the fecal microbiome and metabolomic profiles of healthy research dogs administered antibiotics. J Vet Intern Med. 2019. pubmed.ncbi.nlm.nih.gov/31268578
- Whittemore JC, et al. Longitudinal changes in the fecal microbiome of dogs given antibiotics with or without a synbiotic. 2021. pubmed.ncbi.nlm.nih.gov/34124225
- Fenimore A, et al. Evaluation of metronidazole with and without Enterococcus faecium SF68 in shelter dogs with diarrhea. Top Companion Anim Med. 2017. pubmed.ncbi.nlm.nih.gov/29291770
- Arghavani M, et al. Saccharomyces cerevisiae around a metronidazole course in dogs. 2025. pubmed.ncbi.nlm.nih.gov/39981313
- Westermarck E, et al. Tylosin-responsive chronic diarrhea in dogs: effect of Lactobacillus rhamnosus GG. J Vet Intern Med. 2005. pubmed.ncbi.nlm.nih.gov/15822561
- Torres-Henderson C, et al. Effect of Enterococcus faecium strain SF68 on gastrointestinal signs and fecal microbiome in cats administered amoxicillin-clavulanate. 2017. pubmed.ncbi.nlm.nih.gov/29291771
- Slaughter A, et al. SF68 and the fecal microbiome of cats given amoxicillin-clavulanate. 2026. pubmed.ncbi.nlm.nih.gov/41923274
- Stokes JE, et al. Prevention of clindamycin-induced gastrointestinal signs using a synbiotic in healthy research cats. 2017. pubmed.ncbi.nlm.nih.gov/28755457
- D'Angelo S, et al. Effect of Saccharomyces boulardii in dogs with chronic enteropathies: double-blinded, placebo-controlled study. Vet Rec. 2018. pubmed.ncbi.nlm.nih.gov/29212912
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