Prednisolone is a corticosteroid that reduces inflammation and suppresses the immune system in cats. It’s one of the most commonly prescribed medications in feline medicine, used to treat everything from allergies and asthma to inflammatory bowel disease and certain cancers. If your vet has prescribed it, or you’re trying to understand why your cat might need it, here’s what it actually does and what to expect.
How Prednisolone Works in Cats
Prednisolone is a synthetic version of cortisol, the stress hormone the body naturally produces. It enters your cat’s cells and changes which genes are switched on or off, ultimately dialing down the body’s inflammatory and immune responses. In practical terms, it stops the production of the chemical signals that cause swelling, redness, pain, and immune overreaction. It also reduces the number and activity of white blood cells, which is why it works for conditions where the immune system is attacking the body’s own tissues.
This broad mechanism is what makes prednisolone so versatile. At lower doses it calms inflammation. At higher doses it suppresses the immune system enough to treat autoimmune diseases or slow certain cancers.
Why Prednisolone Instead of Prednisone
You may have heard of prednisone, a closely related drug commonly used in dogs and humans. Cats are different. Prednisone is inactive on its own and must be converted by the liver into prednisolone before it works. Cats are significantly less efficient at making that conversion. A study published in Veterinary Dermatology measured blood levels in cats given each drug and found that prednisolone produced nearly five times higher peak levels of active medication compared to prednisone. The area under the curve, a measure of total drug exposure, was roughly 3,230 ng/mL/h for prednisolone versus just 673 ng/mL/h for prednisone. That’s a dramatic difference, and it’s why virtually all veterinarians prescribe prednisolone rather than prednisone for cats.
Conditions It Treats
Prednisolone is used across a wide range of feline conditions, with the dose tailored to the goal. At anti-inflammatory doses (typically 1 to 2 mg/kg daily), it treats:
- Feline asthma: reduces airway inflammation so your cat breathes more easily
- Allergic skin disease: calms itching, redness, and swelling from environmental or food allergies
- Inflammatory bowel disease (IBD): quiets the gut inflammation that causes chronic vomiting or diarrhea
At higher immunosuppressive doses (around 4.4 mg/kg daily), it’s used for autoimmune conditions where the immune system attacks the cat’s own red blood cells, platelets, or other tissues. It also plays a role in cancer treatment, particularly feline lymphoma, where it’s often part of a chemotherapy protocol.
In most cases, the vet starts at a dose high enough to get symptoms under control, then gradually reduces to the lowest amount that keeps your cat stable.
Common Short-Term Side Effects
Most cats experience some predictable changes when they first start prednisolone. These are dose-dependent, meaning higher doses produce more noticeable effects:
- Increased thirst and urination: the most common change owners notice. Your cat may visit the water bowl and litter box much more frequently.
- Increased appetite: many cats become noticeably hungrier, sometimes to the point of begging or scavenging food.
- Low energy: a general decrease in activity level is common early on.
- Worsening of existing infections: especially bacterial skin infections, which can flare because the immune system is being dialed down.
- Nausea or vomiting: less common, but some cats experience stomach upset.
These side effects often become less noticeable as the dose is tapered down. They’re generally manageable at lower maintenance doses.
Long-Term Risks
When prednisolone is used for more than three to four months, especially at higher doses, the risk profile changes significantly.
Urinary tract infections are one of the most common complications, affecting up to 30% of cats on long-term steroids. What makes this particularly tricky is that prednisolone suppresses the very inflammation that normally signals a UTI. Your cat won’t show the usual symptoms like straining or crying in the litter box. The infection can be completely silent, detectable only through a urine culture.
Diabetes is another serious concern. Prednisolone raises blood sugar, and cats that are already borderline diabetic can tip into full diabetes during treatment. In many cases, the diabetes resolves once the steroid is stopped, but not always. Cats with existing diabetes or a history of diabetes should generally not take prednisolone unless there’s a life-threatening reason.
Other long-term effects include thinning skin and a poor hair coat, slow wound healing, muscle weakness from protein breakdown, weight gain from the increased appetite, and a condition called calcinosis cutis where calcium deposits form hard plaques in the skin. Cats also become more vulnerable to bacterial and fungal infections over time because their immune defenses are chronically weakened.
At high doses over extended periods, cats can develop iatrogenic Cushing’s syndrome, a condition where the body behaves as though it’s producing far too much cortisol on its own. This causes a cluster of symptoms including a pot-bellied appearance, skin changes, and metabolic disruption.
Why Tapering Matters
You should never stop prednisolone abruptly if your cat has been on it for more than a short course. When a cat receives corticosteroids from an outside source, its adrenal glands gradually stop producing their own cortisol. Stopping suddenly can leave the body without enough cortisol to function normally, which can be dangerous.
Tapering is typically attempted once a cat has been clinically stable or in remission for at least two weeks. The standard approach reduces the dose by no more than 25% every two to four weeks. This gives the adrenal glands time to wake back up and resume normal cortisol production. The entire process of reaching the lowest effective dose can take weeks to months.
Drug Interactions and Contraindications
Prednisolone should never be combined with nonsteroidal anti-inflammatory drugs like aspirin or carprofen. The combination dramatically increases the risk of stomach or intestinal ulceration and bleeding. If your cat is taking any pain medication, make sure your vet knows before starting prednisolone.
Certain diuretics, when combined with prednisolone, can cause dangerous drops in potassium levels. The salt retention that prednisolone causes can also be problematic for cats with congestive heart failure or any condition requiring sodium restriction.
One particularly important consideration for cats is dormant upper respiratory infections. Many cats carry herpesvirus or calicivirus in a dormant state after a past respiratory infection. Prednisolone can reactivate these viruses, causing a flare of sneezing, nasal discharge, and eye symptoms. More seriously, if a cat has an undiagnosed internal fungal infection, immunosuppression from prednisolone can allow that infection to spread and become life-threatening.
Prednisolone should not be used in pregnant cats, as it can induce labor.
Monitoring During Treatment
If your cat is on prednisolone long-term, expect regular veterinary check-ups that include bloodwork and urine testing. Periodic urine cultures are especially important because of the high rate of silent urinary tract infections. Standard urinalysis alone won’t catch these since the usual inflammatory markers are suppressed by the medication. A culture, which grows any bacteria present in the urine, is often the only reliable way to detect them.
Blood glucose monitoring matters too, particularly in overweight cats or those with any history of blood sugar issues. Your vet will also watch for changes in liver and kidney values and signs of infection that your cat might not be showing outwardly. At home, tracking your cat’s water intake, appetite, weight, and energy level gives you useful data to share at visits.