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Struvite Bladder Stones In Your Dog

You can read another article on bladder stones here and one on oxalate stones here.  

Ron Hines DVM PhD

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Struvite bladder and kidney stones are made up of magnesium, ammonium and phosphate. They are also called triple phosphate stones, infectious stones and urease stones.

They occur when your pet develops a chronic urinary tract infection (bacterial cystitis) with certain bacteria that have the power to make the urine less acid. These bacteria have the ability to convert urine urea into ammonia because of a certain enzyme they contain called urease. Proteus, Staphylococcus and Klebsiella bacteria are usually the culprits. Ammonia in the urine changes it's odor. It also is toxic to bladder cells and causes the urine pH (acidity/alkalinity) to shift detrimentally toward stone formation.

Once the stone formation process begins, these bacteria live within the stone itself where they are protected from the pet's natural defenses and the effects of antibiotics. Because these stones are rough, they abrade the lining of the bladder causing discomfort and blood in the urine. Their sheer size may limit the amount of urine the bladder can hold causing the continual urgency to void.

These offending bacteria normally reside in the bowel where they cause no problems. But when they move up the urethra and into the bladder, the body has few ways to control them. Because the urethra of females is much shorter than males, this condition is usually a girl-dog problem. I humans, we know that constipation predisposes the body to cystitis. So be sure your dog gets plenty of fiber in its diet. Exercise also seems to help prevent cystitis. Fat dogs are also more at risk of cystitis because their vagina remains damp. Infantile, invaginated vaginas are also quite common in dogs spayed too early.

The average age when dogs develop struvite bladder stones is about two to three years. It is particularly common in cockers, schnauzers, beagles and dachshunds.

Some dogs with bladder stones show few symptoms. I often pick these stones up when I palpate the abdomen of dogs during their yearly routine physicals. But most owners notice increased frequency and straining when urinating or abnormally pink urine. Some of these dogs itch and will scoot along their bottom. Occasionally, owners will find small pea-sized stones on the carpet.

To determine if the stones are struvite, they must be analyzed by a commercial laboratory although the ph of the urine is a strong indicator of the type of stone.


Bladder and kidney stones are porous and bacteria living inside them are very safe from antibiotics. Of critical importance in treating struvite stones is an antibiotic sensitivity test of bacteria found in the dog's urine. Only in this way can we chose the proper antibiotic and the proper dose. The secret of success is to use the right antibiotic at a high enough dose for a long period of time. The antibiotic should be give for at least a month - better yet for one month after x-rays show no remaining stones.


In persistent human cases, nitrofurantoin (Macrodantin), is often administered indefinitely at low doses. It is excreted in the urine and can significantly reduce the risk of infection. It has a very broad activity against many bacteria which makes it unnecessary to know which bacteria are present. There is also a very low rate of resistance when used over long periods.

There are factors other than chronic bladder infection that make some dogs more susceptible to stones than others:

1) Dogs that do not drink enough water

Bladder stones only form in concentrated urine. The more your dog drinks, the less likely the stones are to precipitate (fall) out of solution. Anything that encourages your pet to drink will be helpful. One way is to feed a canned diet. You can diluted even further with a bit of water. But dogs living on canned diets alone will develop tooth problems. This can be prevented by brushing their teeth regularly or providing chewers toys if your pet will use them.

The specific gravity (sp.gr.) or dilution of your pet's first morning urine should be 1.018 or lower. Some urine dip sticks test sp.gr. but they are not very accurate. Better is a refractometer used by your veterinarian or purchased on EBay and used at home. Urine specific gravity is stable so the urine can be kept cool and tested when it is convenient. A less accurate way is to look at the color of your pet' urine. The less intense the yellow color, the better.

2) Maintaining an acid urine

Struvite crystals only form when the pH (acidity/alkalinity) of the urine is over 7. Pharmacies sell urine dip sticks that check for this they can also be purchased over the Internet. These strips also check for blood in the urine, bacteria, sugar, specific gravity (concentration) and a number of other things that are all helpful in managing a case. The urine tested should be the first-of-the-morning and tested within 5 minutes of collection. Only a few drops of clean urine are required. Many owners tape the strip to a wooden stick and dangle it below the dog as she urinates. A less expensive, less accurate but effective method is using litmus paper - available in craft stores and also on the Internet.

3) Diets low in magnesium and protein

Specialty diets are also very helpful. These diets are also formulated to maintain proper urine pH. With time, these diets are often sufficient to dissolve struvite crystals. If one brand does not do the trick, try another such as Hills s/d, CNM's (Purina) NF diet, Hills U/D and K/D diets or Waltham's Low Protein Diet.
Some are not recommended for indefinite us because they are so low in mineral. Some have been reformulated to help prevent oxalate crystals as well.

Despite label warnings regarding long term use in certain cases there is no choice and long term feeding is the only way to save the pet's life. Some of these diets are very high in fat and should not be fed to dogs at risk for pancreatitis.

Early while on these diets, a danger is that the size of the stones reduce so much that they pass into and block the urethra. So one must be on the lookout for a sudden inability to urinate.

4) Urinary Acidifiers

If diet will not maintain an acid pH, or if the pet refuses to eat it urinary acidifiers are another option. Some on the market are: Methio-Form, methigel, Uroeze, Urikare. Begin with one in which d-l methionine is the active ingredient because these are safest. It may require a combination of products to achieve the proper urine pH. Warning too low a urine pH is also dangerous so do not overdo it. Remember that diets formulated for this problem already contain these ingredients and giving additional acidifiers may be dangerous. .

Fighting struvite crystals puts can put your dog at risk for other problems. One is the formation of Oxalate bladder stones which occurs in concentrated acid urine. However, keeping the urine dilute is a good safeguard against this. Specialty diets often contain added salt . We do not know if high salt predisposes dogs to high blood pressure as in humans.

Occasionally, bacterial infection is due to some anatomical defect causing urine pooling within the kidneys, ureters or bladder where bacteria can live. These defects are quite rare. They are either inherited defects or caused by prior surgery such as spaying. A contrast dye x-ray would detect such defects. Such a study would most likely be done if standard treatments fail.

Removing stones

If it is determined that not enough time is present to dissolving the stone(s) with diet, struvite stone are often removed surgically. When the stones are small enough to pass through the urethra, a safer technique is urohydropropulsion which can force all or most of the stones to be eliminated via the urethra by means of a high pressure catheter

Non-antibiotic supplements

There are many herbs , nutrients and homeopathic remedies that are sold to aid in chronic cystitis. None have been scientifically proven to have any benefits.