Lowering BUN (blood urea nitrogen) in dogs depends entirely on what’s driving it up. A normal BUN range for dogs is 8 to 28 mg/dL, and levels above that signal the kidneys are struggling to clear waste, the body is dehydrated, or something else is flooding the bloodstream with nitrogen. The right approach combines treating the underlying cause with dietary changes, better hydration, and sometimes supplements that help the gut pick up slack for the kidneys.
Why BUN Rises in the First Place
BUN measures how much urea, a waste product from protein breakdown, is circulating in the blood. Healthy kidneys filter it out efficiently. When something disrupts that process, urea accumulates. Veterinarians classify the problem into three categories based on where the breakdown occurs.
Pre-renal causes are the most common and often the most fixable. Dehydration, heart failure, and shock all reduce blood flow to the kidneys. Less blood reaching the kidneys means less filtering. The good news: once blood flow is restored, BUN typically drops back to normal because the kidneys themselves are still healthy.
Renal causes mean the kidneys are directly damaged. This is the scenario most owners fear, and it requires the most sustained management. BUN doesn’t rise from kidney disease until roughly 75% of functioning kidney tissue is already lost, which means elevated levels often reflect advanced disease. Chronic kidney disease (CKD) is staged using the International Renal Interest Society (IRIS) system, which was most recently updated in 2023. Staging is based on repeated fasting creatinine measurements, urine protein levels, and blood pressure.
Post-renal causes involve a physical blockage or rupture in the urinary tract, like a urethral obstruction or a ruptured bladder. Once urine flow is restored, BUN resolves.
Adjust Protein in the Diet
Because BUN is a byproduct of protein metabolism, the amount and quality of protein your dog eats has a direct effect on their levels. This is the single most impactful change you can make at home, particularly for dogs with chronic kidney disease.
Research on dogs with experimentally induced kidney failure shows the difference clearly. Dogs fed a high-protein diet (around 44% protein on a dry weight basis) developed severe uremic symptoms: vomiting, mouth ulcers, dehydration, loss of appetite, and lethargy. Six of eleven dogs on that diet died from complications. Dogs fed moderate-protein diets (about 17% dry weight) or restricted-protein diets (about 8% dry weight) showed none of those signs and maintained lower BUN levels throughout the study.
Most veterinary nutritionists recommend a moderate protein level in the range of 14 to 18% dry weight for dogs in kidney failure. The goal isn’t to eliminate protein, which would cause malnutrition, but to reduce the nitrogen load the kidneys have to handle. A minimum of 1.25 to 1.6 grams of high-quality protein per kilogram of body weight per day keeps your dog nourished without overwhelming damaged kidneys. “High-quality” means proteins with a complete amino acid profile, like eggs or lean meats, so less goes to waste.
If your dog is losing protein in the urine (a condition called proteinuria, which your vet can measure), an additional gram of dietary protein should be added for each gram lost. Prescription renal diets from your vet are formulated to hit these targets while also controlling phosphorus and sodium.
Increase Water Intake
Dehydration is one of the fastest ways to spike BUN because it reduces the volume of blood flowing through the kidneys. Keeping your dog well-hydrated helps the kidneys flush urea more efficiently. For dogs with kidney disease, hydration is an ongoing priority rather than a one-time fix.
Practical strategies that work: place multiple water bowls around your home so your dog doesn’t have to go far to drink. Refresh the water daily, since many dogs avoid stale water. Switching from dry kibble to wet food can significantly boost water intake because canned food is roughly 70 to 80% moisture compared to kibble’s 10%. Some owners add warm water or low-sodium broth to their dog’s food. For dogs with moderate to severe kidney disease, your vet may recommend periodic subcutaneous fluid therapy at home, which delivers hydration directly under the skin.
Keep sodium in check as well. Excessive sodium strains the kidneys’ ability to regulate fluid balance, so choose low-sodium food and treats when possible.
Control Phosphorus Levels
As kidney disease progresses, phosphorus accumulates alongside BUN and creatinine. High phosphorus accelerates kidney damage and makes dogs feel worse, so managing it is a key part of lowering the overall burden on the kidneys.
The first step is a phosphorus-restricted diet, which most prescription kidney foods already provide. When diet alone isn’t enough, veterinarians add phosphate binders, medications given with meals that grab phosphorus in the gut before it can be absorbed. Common options include aluminum hydroxide gel, calcium carbonate, and sevelamer. These are mixed into food or given right at mealtime so they can bind dietary phosphorus as it passes through the digestive tract. Your vet will choose the type and dose based on your dog’s bloodwork.
Support the Gut as a Backup Filter
A concept sometimes called “enteric dialysis” takes advantage of the fact that gut bacteria can consume nitrogen-containing waste, reducing how much the kidneys need to handle. The supplement lactulose, a synthetic sugar, works through this mechanism. It lowers the production and absorption of ammonia in the intestines by shifting gut pH to be more acidic. In that environment, ammonia converts to a form that can’t easily cross back into the bloodstream. Instead, gut bacteria use it as a nitrogen source for their own growth, and it exits the body in stool.
Fiber supplements like psyllium also shift the gut microbiome in helpful directions, promoting beneficial bacteria that produce short-chain fatty acids and further support intestinal health. In dogs, psyllium supplementation has been shown to increase populations of bacteria that produce butyrate, a compound that nourishes the cells lining the colon. These approaches won’t replace kidney function, but they can meaningfully reduce the nitrogen load circulating in the blood.
Treat the Underlying Cause
Dietary and hydration changes manage BUN, but they don’t fix whatever is driving it up. Pre-renal azotemia from dehydration resolves with fluid replacement. A urinary obstruction causing post-renal azotemia resolves once the blockage is cleared. These situations often bring BUN back to normal quickly.
Chronic kidney disease requires long-term management rather than a cure. The 2023 IRIS treatment guidelines recommend angiotensin receptor blockers as first-line treatment for dogs with significant protein loss in the urine, alongside a clinical renal diet. These medications reduce pressure inside the kidney’s filtering units, slowing further damage. For dogs at risk of blood clots from protein-losing kidney disease, antiplatelet therapy may also be recommended.
Other conditions that raise BUN include gastrointestinal bleeding (digested blood acts like a high-protein meal), infections, and certain medications. Identifying and addressing these can bring BUN down without any changes to the kidneys themselves.
What to Monitor Over Time
BUN alone doesn’t tell the full story. Your vet will track it alongside creatinine, phosphorus, urine concentration, and urine protein levels to get a complete picture. The ratio between BUN and creatinine can help distinguish dehydration from true kidney disease, and serial measurements over weeks or months reveal whether the current management plan is working.
For dogs with CKD, expect regular rechecks every few months. The IRIS staging system groups dogs into stages based on creatinine levels, and your dog may move between stages as the disease progresses or stabilizes. Each stage has specific treatment targets, so what works early on may need adjustment later. The goal at every stage is the same: reduce the workload on the kidneys, keep your dog comfortable, and slow progression as much as possible.