Amoxicillin for Cats
Dosage Calculator
Enter your cat’s weight and infection type to get the typical amoxicillin dose range, correct frequency, and how long the course should run. Reference use only — always confirm with your vet.
Amoxicillin Dosage Calculator for Cats
Select your cat’s weight, infection type, and how often your vet has prescribed it. We’ll show the dose range, how many mg per dose, and the expected course length.
Amoxicillin Dosage Chart for Cats — by Weight
A complete reference table showing typical amoxicillin doses at different cat weights, based on the 11–22 mg/kg veterinary dosing range. The 50 mg per dose cap applies to cats over 4.5 kg on twice-daily dosing.
Amoxicillin Dose by Cat Weight (11–22 mg/kg range)
FDA / Plumb's| Cat weight | Low dose (11 mg/kg) | Typical dose (16 mg/kg) | High dose (22 mg/kg) | Max per dose | Twice daily total |
|---|---|---|---|---|---|
| 1.5 kg / 3.3 lb | 16.5 mg | 24 mg | 33 mg | 33 mg | 66 mg/day |
| 2 kg / 4.4 lb | 22 mg | 32 mg | 44 mg | 44 mg | 88 mg/day |
| 2.5 kg / 5.5 lb | 27.5 mg | 40 mg | 50 mg | 50 mg | 100 mg/day |
| 3 kg / 6.6 lb | 33 mg | 48 mg | 50 mg | 50 mg | 100 mg/day |
| 3.5 kg / 7.7 lb ★ | 38.5 mg | 50 mg | 50 mg ↑cap | 50 mg | 100 mg/day |
| 4 kg / 8.8 lb | 44 mg | 50 mg | 50 mg ↑cap | 50 mg | 100 mg/day |
| 4.5 kg / 10 lb | 49.5 mg | 50 mg | 50 mg ↑cap | 50 mg | 100 mg/day |
| 5 kg / 11 lb | 50 mg ↑cap | 50 mg | 50 mg ↑cap | 50 mg | 100 mg/day |
| 6 kg / 13.2 lb | 50 mg ↑cap | 50 mg | 50 mg ↑cap | 50 mg | 100 mg/day |
What Infections Does Amoxicillin Treat in Cats?
Amoxicillin vs Clavamox — what is the difference?
Why you must never use human amoxicillin for cats
How Amoxicillin Works in Cats
Amoxicillin is one of the most commonly prescribed antibiotics in veterinary medicine. It belongs to the penicillin family and works by targeting the cell walls of susceptible bacteria, making it an effective choice for several of the infections cats commonly develop.
When a bacterium tries to build or repair its cell wall, amoxicillin binds directly to specific proteins in the wall structure and blocks that process. Without a stable cell wall, bacteria cannot survive. This is why amoxicillin kills bacteria rather than just slowing their growth. It is classified as a bactericidal antibiotic, meaning it actively destroys the target bacteria rather than just holding them in check.
The drug is active against both gram-positive and some gram-negative bacteria, which makes it reasonably broad in its coverage. For cats, it is most often prescribed for upper respiratory infections, urinary tract infections, skin infections, and bite wound infections. These all tend to involve bacteria that are susceptible to penicillin-class antibiotics.
A point worth knowing: the FDA-approved once-daily labeled dose for cats is generally considered outdated by current veterinary practice. Most vets now prescribe amoxicillin every 8 to 12 hours instead, because pharmacokinetic studies show that cats metabolise it more quickly than the original labeling assumed. If your vet prescribes it twice or three times daily, that is standard current practice.
Side Effects of Amoxicillin in Cats
Amoxicillin is generally well-tolerated in cats. The most common issues are digestive, and they usually resolve within a day of stopping the medication. Serious reactions are rare but worth knowing about.
| Side effect | Severity | What to do |
|---|---|---|
| Vomiting or nausea | Mild | Give future doses with a small amount of food. Usually resolves within a day. |
| Diarrhoea | Mild | Common — antibiotics disrupt gut bacteria. Usually self-limiting. Probiotics can help. |
| Reduced appetite | Mild | Often temporary. If your cat stops eating entirely for more than 24 hours, call your vet. |
| Skin rash or hives | Moderate | Stop the medication and contact your vet the same day. |
| Face or paw swelling | Serious | Signs of an allergic reaction. Stop immediately and seek emergency vet care. |
| Difficulty breathing | Serious | Emergency. Go to a vet immediately — this is anaphylaxis. |
| Prolonged lethargy | Moderate | Some tiredness during infection is normal. Extreme lethargy lasting more than 2 days needs vet review. |
True penicillin allergy in cats is rare but it does occur. If your cat has previously had a reaction to amoxicillin, penicillin, or cephalosporins, tell your vet before any antibiotic prescription. There is a cross-reactivity risk between penicillin-class antibiotics and cephalosporins (another common antibiotic group), so the entire class may need to be avoided.
Extended use of amoxicillin beyond 30 days can disrupt the balance of beneficial bacteria in the gut, leading to more persistent digestive issues. This is why course length matters. Longer is not better with antibiotics — the goal is the shortest effective course that clears the infection.
How to Give Amoxicillin to a Cat
Cats are notoriously resistant to taking medication. Amoxicillin comes in several forms and there are genuinely effective strategies that make the process much less stressful for both of you.
Amoxicillin for Cats — Questions and Answers
Common questions about amoxicillin dosage, how to give it, side effects, what it treats, and when it is not the right antibiotic.
The standard veterinary dosage is 11 to 22 mg per kg of body weight, given every 8 to 12 hours. The FDA-approved labeled dose is 50 mg per cat once daily, but most vets now consider once-daily dosing insufficient for most infections and prescribe it more frequently instead.
In practice, most cats receive a 50 mg dose regardless of weight once they exceed approximately 3.5 kg, because there is an informal safety cap at 50 mg per dose. For cats under 3.5 kg, the dose is calculated by weight.
For a 4 kg cat at the standard 11 to 22 mg/kg dosing range, the calculated dose would be 44 to 88 mg. However, because of the practical 50 mg per dose cap used by most vets, a 4 kg cat typically receives 50 mg per dose.
On a twice-daily schedule, that is 100 mg per day total. This is the single most common amoxicillin prescription for average-sized adult cats in the 3.5 to 6 kg range. Your vet confirms the exact dose and frequency based on what your cat is being treated for.
This depends on what your vet prescribed. The three options are:
- Once daily (q24h): The FDA-labeled dose, but generally no longer considered effective for most infections. Rarely prescribed this way in current veterinary practice.
- Twice daily (q12h): The most common prescription. Give roughly every 12 hours — morning and evening, for example. This is now the standard off-label dosing used by most vets.
- Three times daily (q8h): Used for more serious infections. Every 8 hours means three evenly spaced doses throughout the day.
Always follow what was written on your dispensed medication, not a general guideline from the internet. The frequency your vet chose is specific to the infection being treated.
Vomiting is the most common side effect of amoxicillin in cats, and it is usually triggered by giving the medication on an empty stomach. The fix is straightforward — give all future doses with a small amount of food. Even a teaspoon of wet food before the tablet or liquid is enough to significantly reduce nausea.
If your cat continues to vomit even when given with food, or if vomiting is severe, contact your vet. Persistent vomiting may mean the antibiotic is not being absorbed properly, which would make the treatment ineffective. Your vet may switch to a different formulation or antibiotic.
No. Human amoxicillin liquid formulations like Amoxil contain artificial sweeteners, bubble-gum flavouring, and sometimes xylitol. These additives are harmful to cats. Xylitol in particular can cause serious toxicity.
Human capsules (250 mg and 500 mg) are also far too concentrated to dose accurately for cats. A 4 kg cat needs approximately 50 mg. A standard human 250 mg capsule contains five times that amount. Attempting to split or estimate the dose from a human capsule is dangerous.
Amoxicillin for cats must be a veterinary formulation — either Amoxi-Tabs (tablets) or Amoxi-Drops (liquid suspension). Both are specifically formulated for use in cats and dogs without the additives present in human products. Amoxicillin is a prescription antibiotic — you need a vet to prescribe it regardless of formulation.
Reduced appetite is a common and usually temporary side effect of amoxicillin. Many cats eat slightly less for the first day or two of a course, particularly if the antibiotic is causing mild nausea. Giving doses with food often helps.
The important distinction is between reduced appetite and not eating at all. A cat that is eating less is usually fine. A cat that refuses all food for more than 24 hours during a course of amoxicillin should be checked by a vet, because prolonged inappetence raises the risk of hepatic lipidosis (fatty liver disease), which can develop quickly in cats that stop eating.
Also consider that the underlying infection itself often reduces appetite — improvement in eating is actually one of the signs that the antibiotic is working.
Amoxicillin starts working within 1 to 2 hours of the first dose, but visible improvement in your cat's symptoms typically takes 2 to 3 days. This is normal — the antibiotic is reducing the bacterial population with each dose, but clinical signs take time to resolve as the body heals.
If you see no improvement at all after 5 days, contact your vet. This may mean the infection is caused by bacteria that do not respond to amoxicillin, or the diagnosis needs revisiting. Do not just continue the course if there is no progress — infections that do not respond to a first antibiotic choice need re-evaluation.
If amoxicillin is not producing improvement, there are several possibilities and alternatives your vet may consider:
- Amoxicillin-clavulanate (Clavamox): Adding clavulanate extends the antibiotic's coverage to bacteria that have developed resistance to plain amoxicillin. This is very often the next step and is more commonly prescribed than plain amoxicillin for many cat infections.
- Doxycycline: Used for respiratory infections caused by Mycoplasma or Chlamydophila felis, which do not respond to penicillin-class antibiotics at all. Also used for cat bite fever and some tick-borne diseases.
- Clindamycin: Often preferred for dental infections and abscesses because it penetrates bone and soft tissue well. Better coverage of anaerobic bacteria than amoxicillin.
- Cephalosporins (cephalexin, Convenia injection): Useful for skin and some urinary infections. Convenia is a single long-acting injection that lasts 14 days, which many cat owners prefer over daily oral medication.
Your vet may take a bacterial culture and sensitivity test from the infection site before choosing an alternative. This identifies exactly which bacteria are present and which antibiotics will actually kill them.
No. Completing the full course is one of the most important things you can do once an antibiotic is started. When your cat looks better at day 3 or 4, the antibiotic has reduced the bacterial population enough that symptoms have eased — but not eliminated it entirely. The remaining bacteria are often the hardier, more resistant ones.
Stopping early allows those bacteria to regrow. The resulting infection is harder to treat because the surviving bacteria have been exposed to the antibiotic and may have developed some resistance. You may end up needing a longer course or a stronger antibiotic to achieve what the original course would have accomplished.
Always complete every dose unless your vet explicitly tells you to stop early for a specific medical reason.
Calculate your cat's amoxicillin dose
Enter weight and infection type above to get the typical dose range and course length as a reference for your vet conversation.