Doxycycline is the first-line antibiotic for treating bacterial pneumonia in cats, recommended by the International Society for Companion Animal Infectious Diseases (ISCAID) for mild cases. For more severe infections, vets typically reach for amoxicillin-clavulanate or fluoroquinolones, depending on the bacteria involved and how sick the cat is. The specific antibiotic your vet chooses depends on the type of pneumonia, the suspected pathogen, and whether your cat is showing systemic signs like fever or difficulty breathing.
Doxycycline: The First Choice for Mild Cases
For cats with mild bacterial pneumonia and no signs of fever, dehydration, lethargy, or respiratory distress, doxycycline is the go-to antibiotic. It’s especially effective against two of the most common culprits in feline respiratory infections: Bordetella bronchiseptica and Mycoplasma species. Cats that come from shelters, boarding facilities, or multi-cat households are particularly likely to carry these bacteria, making doxycycline a strong empiric choice before culture results come back.
A standard course runs 7 to 10 days, though pneumonia cases often require longer treatment than a simple upper respiratory infection. Your vet will determine the exact duration based on how your cat responds.
There’s an important safety detail with doxycycline in cats. Cats have slow esophageal transit times for pills, meaning tablets and capsules can get stuck partway down and cause esophageal irritation or even strictures (scarring that narrows the esophagus). To prevent this, always follow doxycycline with at least 2 mL of water or a small amount of food, or give the pill coated in a lubricating substance or tucked into a pill treat. This isn’t optional. Esophageal damage from stuck pills is a well-documented problem in cats.
Amoxicillin-Clavulanate for Broader Coverage
Amoxicillin combined with clavulanic acid (sold under brand names like Clavamox) is another common choice for feline pneumonia. The clavulanic acid component disables the defense mechanism that some bacteria use to resist plain amoxicillin, broadening the drug’s reach. This combination is typically given twice daily and works well against many of the gram-negative bacteria that dominate feline lower respiratory infections.
Plain amoxicillin alone is listed as a first-line option for upper respiratory infections in cats, but pneumonia cases often call for the broader coverage that the clavulanate combination provides, especially when the specific bacteria haven’t been identified yet.
Which Bacteria Are Most Common
Knowing what’s causing the infection shapes which antibiotic works best. A study of lower respiratory tract samples from cats in England found that gram-negative bacteria dominated, with Pasteurella species accounting for 37% of feline isolates. Enterobacteriaceae made up about 15%, and non-fermenting gram-negative bacteria accounted for 18%. Bordetella bronchiseptica, while a major player in dogs, was relatively uncommon in feline samples.
This is why vets often recommend a culture and sensitivity test for pneumonia cases. The test identifies the exact bacteria and which antibiotics will kill them. Resistance patterns vary: E. coli isolates from feline respiratory samples showed multidrug resistance (resistance to three or more drug classes) in 23% of cases. Relying on the wrong antibiotic wastes time your cat doesn’t have.
Fluoroquinolones for Severe or Resistant Infections
When pneumonia is severe, doesn’t respond to first-line treatment, or involves resistant bacteria, vets may turn to fluoroquinolones like enrofloxacin or marbofloxacin. These drugs penetrate deep into tissues and are effective against intracellular pathogens, making them useful for entrenched lung infections.
However, fluoroquinolones carry a serious cat-specific risk: retinal damage. Cats have a genetic variation in a protein that normally prevents drugs from accumulating in the retina. Because this protein doesn’t function properly in cats, fluoroquinolones can build up in the eye, generate damaging molecules when exposed to light, and cause retinal degeneration and permanent blindness. Enrofloxacin at doses above 5 mg/kg per day has been linked to this problem. Marbofloxacin is generally considered safer for cats, but the risk isn’t zero. These drugs are reserved for cases where the benefit clearly outweighs the danger.
Aspiration Pneumonia May Need Combination Therapy
Aspiration pneumonia, which happens when a cat inhales food, vomit, or liquid into the lungs, often involves a mix of bacterial types including anaerobes (bacteria that thrive without oxygen). This mixed infection profile means a single antibiotic may not cover everything. Vets frequently use combination therapy in these cases, pairing a broad-spectrum antibiotic with one that targets anaerobic bacteria specifically.
Aspiration pneumonia also tends to be more acute and severe than community-acquired bacterial pneumonia. Cats with this type often present with sudden respiratory distress, fever, and lethargy, which means treatment typically starts with injectable antibiotics in a hospital setting before transitioning to oral medications at home.
How Long Treatment Lasts
Simple upper respiratory infections in cats are usually treated for 7 to 10 days, but pneumonia requires a longer course. Most vets treat bacterial pneumonia for a minimum of 3 to 4 weeks, and some cases need 6 weeks or more. The standard approach is to continue antibiotics for at least 1 to 2 weeks past the point where chest X-rays look normal and clinical signs have resolved. Stopping too early is one of the most common reasons for relapse.
During treatment, expect follow-up visits for repeat X-rays to track how well the lungs are clearing. Your vet may also recheck bloodwork to confirm that infection markers are trending in the right direction. If your cat isn’t improving within the first 48 to 72 hours of treatment, that’s typically the point where your vet will reassess the antibiotic choice and consider culture results or a switch in medication.
Giving Pills to Cats Safely
Administering oral antibiotics to cats is notoriously difficult, but with pneumonia the stakes are high and missed doses can set back recovery. Beyond the esophageal risk already mentioned with doxycycline, clindamycin capsules are another medication known to cause esophageal strictures in cats if they lodge in the throat.
For any oral medication, the safest approach is to follow the pill with a syringe of water (at least 2 mL), wrap it in a pill pocket or treat, or ask your vet about liquid formulations. Some antibiotics, like amoxicillin-clavulanate, come in liquid suspensions that are easier to administer. If your cat absolutely refuses oral medication, your vet may have injectable alternatives for the initial phase of treatment.