Amoxicillin is the most commonly recommended antibiotic for uncomplicated urinary tract infections in cats. International veterinary guidelines list it as the first-line choice, typically prescribed for 3 to 5 days for a simple, one-time infection. But before any antibiotic is started, your vet will likely want to confirm the infection is actually bacterial, because the majority of cats showing urinary symptoms don’t have a bacterial infection at all.
Why Diagnosis Comes Before Antibiotics
This is the most important thing cat owners need to understand: urinary symptoms in cats are usually not caused by bacteria. Between 55% and 67% of cats with lower urinary tract signs, things like straining to urinate, frequent trips to the litter box, or blood in the urine, actually have feline idiopathic cystitis (FIC). That’s a stress-related inflammatory condition with no bacterial cause. FIC often resolves on its own, which historically led people to believe the antibiotics were working when the condition was simply running its course.
Because bacterial UTIs are relatively uncommon in cats compared to dogs, veterinary guidelines recommend confirming the infection with a urine culture before starting any antibiotic. This means your vet will collect a urine sample, often by inserting a needle directly into the bladder (a quick procedure called cystocentesis), and send it to a lab. The culture identifies exactly which bacteria are present and which antibiotics will kill them. This step prevents unnecessary antibiotic use and ensures the right drug is chosen if bacteria are confirmed.
First-Line Antibiotics for Cat UTIs
For a straightforward, first-time bacterial UTI, veterinarians have two main options:
- Amoxicillin: The preferred first choice in most regions. It’s given orally every 8 to 12 hours. If plain amoxicillin isn’t available, amoxicillin combined with clavulanic acid (a combination that broadens its effectiveness against resistant bacteria) is a suitable substitute.
- Trimethoprim-sulfonamide: An alternative first-line option, given orally every 12 hours. It works well but carries a slightly higher risk of side effects compared to amoxicillin.
Your vet will choose between these based on the culture results, your cat’s health history, and what’s available locally. In most cases, amoxicillin is the starting point because it’s effective, well-tolerated, and inexpensive.
How Long Treatment Lasts
For uncomplicated infections, the International Society for Companion Animal Infectious Diseases recommends just 3 to 5 days of treatment. This is shorter than many cat owners expect, and shorter than what was standard practice for years. Some product labels still list 10 to 14 days for urinary infections, which reflects older prescribing habits rather than current evidence-based guidelines.
The research comparing short courses (1 to 3 days) with longer courses (14 to 21 days) is still limited, with very small study sizes in cats. Current evidence isn’t strong enough to declare one clearly superior. In practice, most vets now lean toward the shorter end for simple infections and reserve longer courses for complicated cases, such as infections involving the kidneys or those in cats with underlying health conditions like diabetes or kidney disease.
The Injectable Option
For cats that are difficult to medicate orally (and many cats are), there’s an injectable antibiotic called cefovecin. A single injection under the skin provides antibiotic activity for about 14 days, eliminating the need for daily pills. In clinical trials, it cleared E. coli, the most common UTI-causing bacterium in cats, in about 77% of treated cats, which was comparable to a 14-day course of oral antibiotics.
Cefovecin is convenient, but it has a drawback: once injected, it can’t be stopped if your cat has a bad reaction. It also shows significant resistance from certain bacteria. Roughly 50 to 60% of Klebsiella species and 90% of Pseudomonas species isolated from feline urine samples in one large study were resistant to it. This is why culture results matter. Your vet needs to know which bacterium is causing the infection before choosing this route.
When Stronger Antibiotics Are Needed
Fluoroquinolones, a more powerful class of antibiotics, are reserved for specific situations: infections caused by bacteria resistant to first-line drugs, or kidney infections (pyelonephritis), where the antibiotic needs to penetrate deeper tissue. These are not first-choice drugs for a routine bladder infection.
Cats are uniquely sensitive to one fluoroquinolone in particular. Enrofloxacin can cause retinal damage and even blindness in cats if the dose exceeds safe limits. When fluoroquinolones are necessary, vets prescribe them carefully, sticking to strict dosing limits and monitoring closely.
Antibiotic Resistance in Cat UTIs
Antibiotic resistance is a growing concern. E. coli causes nearly half of all bacterial UTIs in cats, and about 40% of E. coli isolates from feline urine samples show resistance to amoxicillin and ampicillin. Resistance rates to other common antibiotics, including cephalosporins, fluoroquinolones, and trimethoprim-sulfonamide, range from 15 to 20%.
This is precisely why empirical treatment (prescribing antibiotics based on symptoms alone, without culture results) is problematic. When vets skip the culture step and guess which antibiotic to use, they risk choosing one the bacteria can shrug off. The infection persists, the cat gets another round of antibiotics, and resistant bacteria become more entrenched. A urine culture with sensitivity testing takes a few days to come back, but it dramatically improves the odds of picking the right drug the first time.
Side Effects to Watch For
Most cats tolerate UTI antibiotics without major problems, but gastrointestinal upset is common. Vomiting, diarrhea, and reduced appetite are the side effects you’re most likely to see. Giving the medication with food often helps. Some cats drool excessively after taking oral antibiotics, which is unpleasant but not dangerous.
Less commonly, antibiotics can cause skin reactions like itching, redness, or hives. In rare cases, certain antibiotics can trigger neurological symptoms such as tremors or loss of coordination, or blood disorders that cause unexplained bruising or bleeding. If your cat becomes lethargic, stops eating entirely, has trouble breathing, or shows any sign of bleeding, those warrant immediate veterinary attention.
Which Cats Are Most Likely to Get UTIs
Bacterial UTIs in cats follow a pattern. Young and middle-aged cats rarely get them. The typical cat with a confirmed bacterial UTI is over 10 years old and often has an underlying condition that compromises the bladder’s natural defenses: kidney disease, diabetes, or hyperthyroidism. Cats on long-term corticosteroids are also at higher risk. If your older cat is diagnosed with a UTI, your vet will likely investigate whether one of these conditions is lurking in the background, because treating the UTI without addressing the underlying cause often leads to recurrence.
Recurrent UTIs, defined as three or more infections within a 12-month period, require a different management approach. These cats need a urine culture with every episode, and the antibiotic choice should always be guided by sensitivity results rather than repeating whatever worked last time. The bacterial landscape can shift between infections, and what cleared the first UTI may be useless against the next one.