Azodyl and Renadyl: what the studies show about 'enteric dialysis' probiotics
Sooner or later after a kidney diagnosis, you will hear about Azodyl, and its human-market sibling Renadyl. The pitch is that gut bacteria "eat" uremic toxins, so the intestine does a kind of dialysis. The reviews follow: "we started it and the BUN came down."
This article checks that claim against the actual study numbers. The short version: it is not a dangerous product, but in the controlled studies so far, the effect on kidney values has not been reproduced. If you still want to try it, we also lay out how to give it and how to judge it so the money is not wasted.
- There is one controlled study in cats (Rishniw 2011, 10 cats completed). Over 2 months, BUN and creatinine changes did not differ from the control group (P=0.8). The capsules were opened and sprinkled on food.
- A study of 32 dogs given intact capsules at twice the label dose for a year (Polzin, 2011 conference abstract) also found no difference.
- The positive results come from observations without a control group or human studies run by the manufacturer. A meta-analysis of 16 human trials found no significant drop in urea or in the uremic toxins indoxyl sulfate and p-cresyl sulfate.
- Gut-derived uremic toxins are a real problem (cats with CKD already have higher indoxyl sulfate at stage 2). The question is whether these three bacterial strains fix it.
- If you give it: label dose (2 capsules a day for a 4 kg cat), capsule whole, refrigerated, and judge after 8 weeks using creatinine and SDMA from the same lab. In our app records, one in three cats on Azodyl gets 1 capsule a day, which for most adult cats is half the label dose.
- On a fixed budget, phosphorus control, fluids, nausea control and blood pressure come first. Azodyl is an option for money left over after those.
| Who | Decides |
|---|---|
| You, at home | Whether to give it (it is a supplement), sticking to the label dose, storage, vomiting and stool records, whether to continue after the 8-week trial |
| Together | Test dates before and after 8 weeks, spacing from other drugs and adsorbents |
| Your vet | Finding the cause when values rise (dehydration, infection, stones, blood pressure), adjusting prescription drugs |
1. What Azodyl and Renadyl are
Both are made from the same three bacterial strains developed by the US company Kibow Biotech. Azodyl is Kibow's formula sold for animals by Vetoquinol since 2006; Renadyl is Kibow's own human product. Both are sold as supplements, not drugs, so neither had to pass clinical trials for approval.
| Azodyl (veterinary) | Renadyl (human) | |
|---|---|---|
| Bacteria | Streptococcus thermophilus · Lactobacillus acidophilus · Bifidobacterium longum (the same three) | |
| Count per capsule | 15 billion CFU | 45 billion CFU (current product; 15–30 billion in the trials) |
| Other ingredients | Psyllium husk | Inulin · xylo-oligosaccharides (prebiotics) |
| How to give | Whole, not opened or crushed, on an empty stomach | With meals, twice a day |
| Storage | Refrigerate | Stable at room temperature for 2 weeks; refrigerate (4–8 °C) on arrival |
| Manufacturer's stated time to effect | 6–8 weeks | — |
Azodyl data from the Vetoquinol USA product page, Renadyl from its retail label (checked 2026). In Canada, all Renadyl lots were recalled in 2021 because inulin was not declared on the label, a labelling issue rather than an efficacy or safety one.
2. "Dialysis through the gut": half of it is real
When the kidneys fail, more urea leaks from the blood into the gut. Some meat protein also escapes digestion and reaches the colon, where bacteria ferment it into indole and p-cresol. The liver turns these into the uremic toxins indoxyl sulfate and p-cresyl sulfate, which damage the kidneys further and build up when the kidneys cannot clear them.
This has been shown in cats. Comparing 30 cats with CKD to 11 healthy cats, the CKD cats had less diverse gut bacteria, and indoxyl sulfate was already higher at stage 2 (Summers 2019).
So "change the gut to lower uremic toxins" is a direction researchers take seriously. Azodyl's explanation goes a step further: the added bacteria use nitrogen waste such as urea in the gut as food and carry it out of the body. That second step, whether these three strains actually consume enough to matter, is what the studies have to confirm.
Even if bacteria eat some urea in the gut and BUN drops a little, the kidneys' filtering power (GFR) stays the same. The manufacturer's own FAQ says it does not restore kidney function. That is why this article judges by creatinine and SDMA rather than BUN, plus how the cat is doing (appetite, vomiting).
3. Every study so far, in one table
| Study | Subjects · design | Result | What to note |
|---|---|---|---|
| Ranganathan 2005 | 36 rats with 5/6 kidney removal, 16 weeks | Benefit only in the Sporosarcina pasteurii and L. sporogenes groups | The three-strain mix now in Azodyl was not among the effective groups |
| Palmquist 2006 no online full text | A small number of CKD cats, no control group, sprinkled on food | BUN down about 5–37%, creatinine 0–52% | The most quoted "it works" evidence. With no control, other causes cannot be ruled out |
| Rishniw & Wynn 2011 | CKD cats (stages 2–4), 16 enrolled, 10 completed, randomised, double-blind, 2 months, sprinkled on food | BUN and creatinine changes no different from control (P=0.8) | The only controlled cat study. Control got psyllium only |
| McCain 2011 | 15 tigers, lions and other big cats, no control, 6 months (9 remaining) | BUN unchanged. Creatinine fell between months 2 and 6; baseline to 6 months was borderline (P=0.05) | No control group, and close to half dropped out |
| Polzin 2011 (conference abstract) | 32 dogs with CKD, randomised, placebo-controlled, intact capsules at twice the label dose, 12 months | Bloodwork, body condition and owner-rated quality of life, measured at 7 time points from 1 month to 1 year: no difference at any of them | The answer to "it failed because it was sprinkled". However, some dogs had urinary tract infections and received antibiotics during the year, which may have affected the probiotic. Never published as a full paper |
| Kanakubo 2013 (conference abstract) | 4 dogs on haemodialysis, 1–2 months | Pre-dialysis BUN and gut urea clearance unchanged | Partly funded by the manufacturer |
| Ranganathan 2009 · 2010 | Humans with CKD stages 3–4, placebo crossover. 16 people (13 completed) · 46 people, 6 months | BUN fell (29 of 46). No significant difference in creatinine. 86% said their quality of life improved | All run by the manufacturer (Kibow) |
| Natarajan 2014 | 28 human haemodialysis patients (22 completed), placebo crossover, 180 billion CFU/day | Uremic toxins including indoxyl sulfate and p-cresol, and quality of life: no significant change | Manufacturer-funded. The trial that directly measured "breaks down uremic toxins" |
| McFarlane 2019 (meta-analysis) | 16 randomised human trials, 645 people | Urea −0.30 mmol/L (P=0.76); indoxyl sulfate and p-cresyl sulfate not significantly lower | Prebiotics (fibre) alone did lower urea |
| Liu 2022 (meta-analysis) | 23 randomised human trials, 842 people | Kidney function (eGFR) unchanged (mean difference 0.08) | Toxin reductions mostly in dialysis patients |
Click a study name to open its abstract (PubMed). Polzin and Kanakubo are conference abstracts with no public full text, so they link to an article that summarises them.
The pattern: the better controlled the study, the smaller the effect. Without a control group, the effects of diet, fluids or drugs changed at the same time, and the normal ups and downs of the values, all look like "the Azodyl effect".
Recent studies with other bacteria show a slightly different signal. In a placebo-controlled study of 16 dogs given Enterococcus SF68 for 60 days, indoxyl sulfate fell from 19.1 to 12.8 µmol/L (López 2026; the manufacturer supplied the probiotic). Two cat studies with lactic acid bacteria treats (Taiwan, 2024 and 2025) had no control group, and the one that analysed 14 cats found no significant change in creatinine, BUN, SDMA or uremic toxins. Using probiotics to lower gut uremic toxins is still an open question, but there is no evidence that Azodyl's three strains are the answer. That is where things stand.
4. The cat study in detail: was sprinkling the problem?
Rishniw & Wynn (2011) gave CKD cats either Azodyl or psyllium (the fibre in Azodyl, alone) at the label dose for 2 months, with neither owners nor vets knowing which. BUN and creatinine moved the same way in both groups, and one cat in each group died as the disease progressed. No side effects were reported.
The manufacturer's reply was that opening the capsule and mixing it into food lets stomach acid kill the bacteria. That may be true: Azodyl uses an acid-resistant capsule to protect the bacteria until they reach the intestine. But two things remain.
- The cat observation quoted as positive evidence (Palmquist 2006) was also sprinkled on food. If sprinkling does not work, that positive result is not explained either.
- The dog study with intact capsules at twice the label dose for a year (Polzin 2011) also showed no difference.
So this is how we read it: the weight of evidence says sprinkling does not work, and giving the capsule whole has never been properly tested in cats. The tip passed around English-speaking owner groups, opening the capsule into a teaspoon of butter or cream an hour before a meal, has never been tested. The current Vetoquinol label says "do not open or crush".
5. How to read "we started it and the numbers went down"
To tell whether the numbers in a review are really due to Azodyl, filter them in this order.
- What went down? If only BUN fell, hold off. BUN swings with protein eaten that day, water intake and gut bleeding. Check whether creatinine or SDMA fell too.
- By how much? A cat's creatinine moves from test to test even with no change in care. In a study of 29 senior cats measured repeatedly, the within-cat variation in azotaemic cats was about 7%, and machine error comes on top of that. A dog study found that two consecutive results must differ by more than 24% to show a real change. We use 20% or more, at the same lab, twice in a row as our starting line.
- What else changed at the same time? Starting or increasing fluids, switching to a renal diet, an antiemetic, blood pressure medication or stopping a high-protein diet can all lower creatinine. If any of these changed when Azodyl started, the effects cannot be separated.
- Why was the last value high? After a spike from dehydration or an acute crisis, values often come down regardless of treatment. Check whether the starting point was "usual" or "the worst day".
We checked our own app records too. As of October 2026, 41 cats have Azodyl or Renadyl on their medication list. Only 3 had blood tests both in the 4 months before starting and between 3 weeks and 6 months after, and in all three, fluids or other drugs changed in the same period. That is not enough to say anything either way. We will update this paragraph as records build up.
6. If you give it: dose, how to give it, and an 8-week trial
There can be good reasons to try it even knowing the evidence. It is fairly safe, and many owners feel their cat's appetite improved. But if you try it, do it properly, or you will not be able to judge it.
| Body weight (Azodyl label) | Bacteria per day | Azodyl (15 billion per capsule) | Renadyl equivalent (45 billion per capsule) |
|---|---|---|---|
| Under 2.3 kg (under 5 lb) | 15 billion | 1 capsule · once a day | About 1/3 capsule |
| 2.3–4.5 kg (5–10 lb) | 30 billion | 2 capsules · 1 morning · 1 evening | About 2/3 capsule |
| Over 4.5 kg (over 10 lb) | 45 billion | 3 capsules · 2 morning · 1 evening | 1 capsule |
In our app, 12 of the 34 cats on Azodyl are recorded at 1 capsule a day. Unless the cat is under 2.3 kg, that is half the label dose or less. If you felt "it did nothing", check the dose first.
The three strains are the same, but current Renadyl holds 45 billion per capsule and Azodyl 15 billion. So compare bacteria per day, not capsule counts. One Renadyl capsule matches the Azodyl label dose for a cat over 4.5 kg, and is already 1.5 times the label dose for a 2.3–4.5 kg cat.
- Most cats on Renadyl in our app get 1 capsule a day, which is not short of the Azodyl label dose. Giving "2–3 capsules by weight, like Azodyl" means 2 to 4.5 times the label amount.
- Renadyl is a human product with no dosing table for cats. The Renadyl column above is a conversion matching Azodyl's bacteria count; it has not been shown that the same count gives the same effect.
- Older Renadyl and the products used in the trials held 15–30 billion per capsule. Check the CFU per capsule on your label first.
- Give it whole. Do not open or crush it. After any capsule or pill, follow with 3–6 ml of water by syringe; dry capsules tend to lodge in a cat's oesophagus.
- On an empty stomach. That is what the label says, but if your cat vomits it on an empty stomach, giving it right after a meal is better. A capsule that comes back up counts as a missed dose.
- Keep it refrigerated. It is a live-bacteria product, so a parcel that sat in the heat may hold fewer live bacteria. Put it in the fridge as soon as it arrives.
- If your cat will not swallow capsules: opening them has no evidence behind it. Weighing the daily struggle and the cost, not starting is also a reasonable choice.
The Azodyl label says on an empty stomach (1 hour before or 2 hours after a meal); Renadyl says with or right after a meal. Both companies describe an "acid-resistant capsule" yet give opposite advice, and neither explains why. No study has compared timing either. What follows is reasoning from general principles.
- The case for an empty stomach: a coated capsule is meant to pass through the stomach quickly. Taken with food, it stays in the stomach longer, and such coatings are often designed to dissolve as acidity drops, so it may open early once food has diluted the stomach acid.
- The case for with meals: food buffers stomach acid. In a model of the human upper gut, uncoated probiotics survived best when taken with or just before a meal, especially one containing some fat, and poorly 30 minutes after (Tompkins 2011). Renadyl's "right after a meal" is effectively "with a meal".
- Before starting: creatinine, SDMA, BUN and phosphorus at the same lab, plus body weight. Add it to the app's medication list so the start date is recorded.
- For 8 weeks: keep diet, fluids and drugs unchanged where you can. Record vomiting, stool and appetite.
- After 8 weeks: retest at the same lab. If creatinine or SDMA fell more than 20% and stays there at the next test, it "may be working" and you can continue. A change within 20% means no effect you can see in the numbers.
- Even with no change in numbers, clearly better appetite or less vomiting can be a reason to continue. Equally, if vomiting increased, stop regardless of the numbers.
7. Side effects and combining with other treatments
- Vomiting is the most common problem. The capsule is large enough that some cats bring it up whole hours later, which is why the manufacturer made it smaller. Soft stools are reported occasionally.
- Severely immunocompromised cats: live-bacteria products need care in cats on immunosuppressants or very frail cats. This was among the warnings Canada required after the recall.
- Antibiotics kill the bacteria if given together. Keep them 2–3 hours apart.
- Adsorbents (Kremezin, Porus One) and phosphate binders: adsorbents can bind other drugs and supplements given at the same time, so the rule is to space them from everything else. Phosphate binders must go with food, which naturally separates them from Azodyl on an empty stomach.
- Fibre: Azodyl contains psyllium and Renadyl contains inulin. The amounts are small, but stools may firm up or soften.
8. Where opinions differ
Where we stand: it is an option after the basics. We reached that view because the controlled results (one cat study, two dog studies, human meta-analyses) point the same way, while the positive results have no control group or come from the manufacturer. Still, there is no controlled cat study with whole capsules, so it would be wrong to say "proven not to work". That is why we wrote down how to try it properly.
How to check in your own cat: the 8-week trial in section 6. Change nothing else, test at the same lab, judge by creatinine and SDMA, and your cat will give you the answer.
9. What to spend on first
At US retail, 90 capsules of Azodyl cost about $86–100. For a 4 kg cat (2 capsules a day) that is 45 days, or about $60 a month. Prices elsewhere vary by clinic. Here is where the same money should go first.
| First (do not cut) | Next | If money is left (fine to skip) |
|---|---|---|
| Phosphorus control (renal diet, binders), fluids (sub-Q and drinking), nausea and appetite control, blood pressure and proteinuria drugs, regular tests | Potassium (when low), anaemia treatment, omega-3 | Azodyl, Renadyl and other kidney supplements with weak evidence |
You can compare the evidence grade of each in our drug and supplement compendium.
10. What to bring to the vet
If Azodyl has been suggested or your cat is already on it, bring your records and look at them together instead of only asking questions. The conversation goes faster.
- The start date and capsules per day: check together that it matches the label dose.
- Creatinine and SDMA before and after, from the same lab: see together whether there was a change over 20%, and whether anything else changed in that period.
- Vomiting records: if vomiting increased after starting, this supplement may be the cause.
- A list of the basic care you are doing now: if a phosphate binder, fluids or blood pressure medication is missing, that is a reason to discuss those before Azodyl.
11. Read next
- Porus One vs Kremezin: uremic toxin adsorbents
- Probiotics for cats: when they actually work
- How to read a single creatinine number
- Phosphate binders: what, how much, when
- Uremia: nausea and vomiting, and what to do at home
📌 One-line tip: when starting a new supplement, one at a time, record the start date, and retest at the same lab after 8 weeks. That is the only way to know what worked.