Amoxicillin is one of the most prescribed antibiotics in veterinary medicine — and one of the most misunderstood. The dose that helped your neighbor’s dog may not be right for yours. This guide covers the FDA-approved reference dosing, what infections it actually treats, when it doesn’t work, and the questions your vet wishes you’d ask before reaching for the medicine cabinet.
Amoxicillin questions tend to come in a rush — your dog was just diagnosed, you’re holding a prescription bottle, and you need clarity fast. These are the answers to what dog owners most commonly want to know, before reading the full breakdown.
- 1 What is the standard amoxicillin dose for dogs? The FDA-approved reference dose on the Amoxi-Tabs label is 5 mg per pound of body weight, given by mouth twice daily. A 40-lb dog would receive approximately 200 mg per dose, twice a day. Your vet may prescribe a higher dose — up to 10 mg per pound twice daily — depending on the infection type and severity. Always follow your specific prescription, not a general chart. The dose your dog needs is the one your vet calculated based on your dog’s weight, health history, and what organism is causing the infection.
- 2 Can I give my dog human amoxicillin from my medicine cabinet? No — and this is more dangerous than it sounds. Some human amoxicillin liquid suspensions, especially pediatric formulas, contain xylitol — an artificial sweetener that is acutely toxic to dogs even in small amounts. Human capsule sizes (250 mg and 500 mg) also make accurate weight-based dosing nearly impossible. The inactive ingredients, flavorings, and binders in human formulations differ from veterinary versions and can cause unexpected reactions. Beyond ingredients, using prescription medication without veterinary guidance means your dog may have a viral infection, fungal problem, or resistant bacteria that amoxicillin won’t touch — while delaying the right treatment. Always get a prescription from your vet.
- 3 How long does a course of amoxicillin typically last? The FDA label specifies 5 to 7 days, or 48 hours after all symptoms have completely resolved — whichever is longer. Skin infections, wounds, and mild respiratory infections often fall into this window. Urinary tract infections per current ISCAID guidelines are now commonly treated for just 3 to 5 days in uncomplicated cases. Deeper infections — bone, dental, chronic skin disease — may require 14 to 21 days or longer. Never stop early just because your dog seems better. The infection may have retreated below the detectable surface while still active, and stopping too soon is a reliable way to cause a drug-resistant relapse.
- 4 What infections does amoxicillin treat in dogs? Amoxicillin treats bacterial infections caused by susceptible gram-positive and gram-negative organisms, including Staphylococcus, Streptococcus, E. coli, and Proteus species. Common uses include skin and soft-tissue infections, urinary tract infections, respiratory infections, ear infections, and dental infections. It does not treat viral infections (parvovirus, distemper, kennel cough caused by a virus), fungal infections, parasite-related illness, or bacteria that have developed resistance — including many Staphylococci, where Clavamox (amoxicillin plus clavulanate) is the more appropriate choice.
- 5 What’s the difference between amoxicillin and Clavamox? Clavamox combines amoxicillin with clavulanic acid, which blocks the bacterial enzyme (beta-lactamase) that would otherwise destroy amoxicillin. Plain amoxicillin is ineffective against most Staphylococcus infections — which are the bacteria behind the majority of skin infections in dogs — because staph produces beta-lactamase. Clavamox defeats that resistance mechanism. If your dog has a skin infection, wound, or abscess, your vet will almost always reach for Clavamox rather than plain amoxicillin. Plain amoxicillin is better suited for UTIs, some respiratory infections, and situations where the bacteria are confirmed susceptible.
- 6 My dog is already on amoxicillin but isn’t improving after three days. Should I be worried? Call your vet — don’t wait out the full course hoping for a turn. The FDA label specifically states: “If no improvement is seen in 5 days, review diagnosis and change therapy.” Three days in with no improvement is a signal worth flagging, not something to wait through. The infection may be caused by a resistant organism, a virus that antibiotics can’t touch, or a fungal condition. It may also mean the dose needs adjustment or that a secondary issue is compounding the problem. Your vet may want to run a culture and sensitivity test to identify exactly which bacteria is present and which antibiotic will actually kill it.
- 7 Can I give amoxicillin with food? Yes — amoxicillin can be given with or without food. Unlike some medications, food doesn’t significantly alter the absorption of amoxicillin in dogs. If your dog experiences stomach upset (vomiting, loose stools, or loss of appetite) on an empty stomach, giving it with a small meal or wrapping the tablet in a soft treat usually resolves the issue without affecting how well the medication works. Tablets can also be crushed and mixed into food if your vet approves. Liquid suspension should be refrigerated and discarded after 14 days.
- 8 Is amoxicillin safe for pregnant or nursing dogs? Amoxicillin is generally considered one of the safer antibiotics during pregnancy and nursing, but this decision always belongs to your veterinarian. Penicillin-class antibiotics have been used in pregnant dogs for decades with a reasonable safety record, but dosage and course length must still be determined based on the individual dog. Inform your vet immediately if you believe your dog may be pregnant before starting any antibiotic. No antibiotic is automatically safe for all stages of pregnancy across all health conditions.
This calculator estimates a reference dose based on the FDA-approved dosing rate on the Amoxi-Tabs label. It is a starting reference only — your veterinarian’s prescription is the correct dose for your dog. Never use this to dose your dog without a current veterinary prescription.
This reference chart uses the FDA-approved standard dose of 5 mg per pound twice daily, as stated on the Amoxi-Tabs veterinary label. Your vet may prescribe a different rate depending on infection type and severity. The “nearest tablet” column shows which tablet strength to ask your vet about for accurate dosing — never split tablets without veterinary approval.
Doses shown are based on the FDA reference rate of 5 mg/lb twice daily. Your vet may prescribe 7.5–10 mg/lb for more serious infections. Liquid suspension (50 mg/mL) should be used for dogs under 10 lbs. Refrigerate liquid; discard after 14 days. Never use this chart to adjust or substitute a prescribed dose.
| Dog Weight | Standard Dose (5 mg/lb) | Per Dose (mg) | Daily Total (mg) | Nearest Tablet | Liquid (50 mg/mL) |
|---|---|---|---|---|---|
| 5 lbs (2.3 kg) | 25 mg twice daily | 25 mg | 50 mg | 50 mg tablet | 0.5 mL |
| 10 lbs (4.5 kg) | 50 mg twice daily | 50 mg | 100 mg | 50 mg tablet | 1 mL |
| 15 lbs (6.8 kg) | 75 mg twice daily | 75 mg | 150 mg | 100 mg tablet* | 1.5 mL |
| 20 lbs (9.1 kg) | 100 mg twice daily | 100 mg | 200 mg | 100 mg tablet | 2 mL |
| 25 lbs (11.3 kg) | 125 mg twice daily | 125 mg | 250 mg | 150 mg tablet* | 2.5 mL |
| 30 lbs (13.6 kg) | 150 mg twice daily | 150 mg | 300 mg | 150 mg tablet | 3 mL |
| 40 lbs (18.1 kg) | 200 mg twice daily | 200 mg | 400 mg | 200 mg tablet | 4 mL |
| 50 lbs (22.7 kg) | 250 mg twice daily | 250 mg | 500 mg | 200 mg tablet* | 5 mL |
| 60 lbs (27.2 kg) | 300 mg twice daily | 300 mg | 600 mg | 400 mg tablet* Large | 6 mL |
| 75 lbs (34 kg) | 375 mg twice daily | 375 mg | 750 mg | 400 mg tablet* | 7.5 mL |
| 90 lbs (40.8 kg) | 450 mg twice daily | 450 mg | 900 mg | 400 mg + 50 mg* | 9 mL |
| 100 lbs (45.4 kg) | 500 mg twice daily | 500 mg | 1,000 mg | 400 mg + 100 mg* | 10 mL |
* Asterisk indicates dose falls between tablet strengths — your vet will round to the nearest appropriate strength. Liquid volume shown is for 50 mg/mL oral suspension. Refrigerate after reconstitution; discard after 14 days. This chart is for educational reference only. Your veterinarian’s prescription takes priority.
The prescribed dose and course length vary significantly depending on what type of infection your dog has. Here’s what vets typically prescribe for each common condition — and what the evidence actually supports.
UTIs are one of the most common reasons amoxicillin is prescribed in dogs — up to 27 percent of dogs will experience a UTI at some point. The International Society for Companion Animal Infectious Diseases (ISCAID) has updated its guidelines to recommend just 3 to 5 days of treatment for uncomplicated lower UTIs, a shift from the older 10 to 14 day standard. For a recurring, complicated, or upper urinary tract infection, your vet will likely prescribe a longer course and may want a urine culture first to confirm the bacteria involved and which antibiotic it responds to. Female dogs are more prone to UTIs than males due to their anatomy. Signs that warrant a call to your vet during treatment: straining to urinate, blood in the urine that isn’t improving by day two or three, or a dog that seems more uncomfortable rather than less after starting the medication.
This is the single most important thing to understand about amoxicillin and skin infections: the most common bacteria behind canine skin infections (pyoderma, hot spots, infected wounds) is Staphylococcus pseudintermedius, and the vast majority of staph strains produce beta-lactamase — an enzyme that renders plain amoxicillin inactive before it can work. Clavamox (amoxicillin plus clavulanate) is specifically designed to defeat this resistance mechanism and is almost always the correct choice for skin infections, abscesses, and soft tissue wounds. When plain amoxicillin is prescribed for skin conditions, it’s typically for confirmed susceptible organisms or superficial infections where culture sensitivity showed it will work. Duration for skin infections treated with either formulation: 5 to 7 days for superficial infections, 14 to 21 days for deeper pyoderma or abscesses.
Amoxicillin treats bacterial respiratory infections — pneumonia caused by susceptible organisms, secondary bacterial complications following viral illness, and some forms of bronchitis. It does not treat the viral component of kennel cough (Bordetella is often viral) or other viral respiratory diseases. Many cases of “kennel cough” resolve on their own without antibiotics, and over-prescribing amoxicillin for self-limiting viral illness is one of the contributors to antibiotic resistance your vet is actively trying to minimize. If your dog has a clear, watery nasal discharge and mild cough, your vet may advise monitoring rather than immediately treating. Thick green or yellow discharge, high fever, and worsening appetite are the signs that a secondary bacterial infection has set in and antibiotics are appropriate.
Oral amoxicillin may be prescribed for ear infections when the infection is severe, involves the middle ear, or when topical treatment alone is insufficient. For most outer-ear (otitis externa) infections, vets prefer topical antibiotic/antifungal ear drops directly in the canal since they deliver a much higher concentration to the infected tissue with minimal systemic drug exposure. Yeast (Malassezia) is responsible for a significant proportion of canine ear infections — and amoxicillin does nothing for yeast. If your dog’s ear problems keep coming back despite antibiotics, ask your vet for a cytology (ear smear under a microscope) to determine if yeast is the primary driver.
Dental and periodontal infections are one of the FDA-approved indications for Clavamox (amoxicillin/clavulanate) in dogs. Oral bacteria in dogs include anaerobic organisms — bacteria that grow without oxygen — and amoxicillin has activity against many of them. Antibiotics for dental disease work best as an adjunct to actual dental treatment (professional cleaning, extraction if needed), not as a standalone cure. A dog with a badly infected tooth that receives antibiotics without the infected tissue being addressed will likely improve temporarily and then relapse. The infection is in a site that requires physical removal of the source. If your vet prescribed antibiotics before a scheduled dental cleaning, that’s normal practice — it helps reduce the bacterial load before the procedure.
This is the comparison that trips up most dog owners — and even some who have been through antibiotic treatment with their dogs multiple times. Understanding when your vet reaches for one versus the other explains a lot about why your previous prescription may have worked while this time a different one was prescribed.
| Feature | Plain Amoxicillin | Clavamox (Amox + Clavulanate) |
|---|---|---|
| Active ingredients | Amoxicillin only | Amoxicillin + clavulanic acid (4:1 ratio) |
| Staph coverage | ❌ Most staph strains resistant | ✅ Effective — clavulanate blocks resistance |
| Skin & wound infections | ❌ Usually wrong choice | ✅ Primary choice |
| UTIs (uncomplicated) | ✅ Often first choice | ⚠️ Used when resistance suspected |
| Dental infections | ⚠️ Sometimes used | ✅ FDA-approved for this use |
| Tablet strengths (vet) | 50, 100, 150, 200, 400 mg | 62.5, 125, 250, 375 mg (combined) |
| Liquid suspension | 50 mg/mL — refrigerate 14 days | 62.5 mg/mL — refrigerate 10 days |
| Typical cost | Lower — ~$15–$30 for a course | Higher — ~$30–$60 for a course |
| FDA-approved for dogs? | ✅ Yes (NADA #055-078) | ✅ Yes (Clavamox brand) |
| Generic available? | ✅ Yes — widely available | ✅ Yes — FDA approved generic 2021 |
Amoxicillin is one of the safer antibiotics in veterinary medicine when used correctly. But “safer” is not the same as “without risk” — and there are specific situations that require immediate veterinary contact.
- ASPCA Animal Poison Control Center: (888) 426-4435 — available 24/7, 365 days a year. Consultation fee may apply.
- Pet Poison Helpline: (855) 764-7661 — available 24/7. Consultation fee may apply.
- FDA — Report Adverse Events: 1-888-FDA-VETS or fda.gov/reportanimalae
Overdose signs: vomiting, diarrhea, severe lethargy, loss of coordination, seizures. Large overdoses can damage the nervous system and liver. Do not wait to see if symptoms resolve — call immediately.
Vomiting, loose stools, diarrhea, and reduced appetite are the most frequently reported side effects of amoxicillin in dogs. These usually appear within the first day or two and often improve as the course continues. Giving the medication with food rather than on an empty stomach frequently resolves the issue. If diarrhea is severe, bloody, or lasts more than two days, contact your vet — severe diarrhea can indicate colitis or a disruption of the gut flora that requires additional treatment.
A small number of dogs are allergic to penicillin-class antibiotics. Signs of an allergic reaction include hives or raised welts on the skin, facial swelling (especially around the muzzle and eyes), intense itching, and redness. In rare but life-threatening cases, anaphylaxis can occur: difficulty breathing, collapse, pale gums, rapid weak pulse, and loss of consciousness. Stop the medication and contact your veterinarian immediately at the first sign of an allergic reaction. The FDA-approved label states clearly: the use of amoxicillin is contraindicated in animals with a known history of allergic reaction to penicillin. If your dog has ever had a reaction to any penicillin drug — including Clavamox, ampicillin, or amoxicillin itself — tell your vet before any antibiotic is prescribed.
Amoxicillin should be used with caution alongside bacteriostatic antibiotics — drugs like tetracycline, chloramphenicol, and erythromycin that slow bacterial growth rather than killing bacteria outright. Combining them can reduce amoxicillin’s effectiveness. Methotrexate (used in cancer treatment) and probenecid can also interact with amoxicillin. Give your vet a complete list of all prescription medications, over-the-counter products, supplements, and herbal remedies your dog takes before any antibiotic course begins. This includes flea preventatives, joint supplements, and anything else that goes into your dog’s mouth regularly.
Tablets should be stored at temperatures between 68°F and 77°F (room temperature) in a tightly closed container, away from moisture and light. Oral liquid suspension must be refrigerated after mixing and discarded after 14 days — liquid that sits at room temperature or goes beyond 14 days begins to lose potency and should not be used even if there’s medication left. Keep all amoxicillin out of reach of children and other pets. Do not store in a bathroom cabinet where humidity accelerates degradation.
The FDA-approved label specifies amoxicillin is for use in dogs and cats only. Never give amoxicillin to rabbits, guinea pigs, chinchillas, hamsters, or other small herbivorous pocket pets — penicillin-class antibiotics disrupt their gut flora in a way that causes life-threatening diarrhea and enterotoxemia, which can be fatal within hours. If you have both a dog and a small animal pet and they share a living space, store medications separately and be careful about cross-contamination.
The questions that bring people to this page tend to cluster around a few specific moments. Here’s the honest answer for each of the most common ones.
Give it at consistent times every day — spacing doses as evenly as possible (every 12 hours for a twice-daily prescription) matters more than hitting exact clock times. Giving it with food reduces the chance of stomach upset without affecting absorption. If your dog refuses tablets, ask your vet whether you can crush them into food or hide them in a soft treat. Finish the entire prescribed course even if your dog seems fully recovered before it ends — stopping early leaves surviving bacteria to repopulate and possibly develop resistance. Note the start date and set a phone reminder for your last dose day.
This happens, and it’s more information than a failure. A relapse after a complete course usually means one of three things: the bacteria was resistant to amoxicillin, the course wasn’t long enough for the depth of the infection, or there’s an underlying structural or immune issue making the dog susceptible to recurrence. Ask your vet for a culture and sensitivity test before the next antibiotic course — this identifies exactly which bacteria is present and which antibiotics it responds to, rather than guessing. For recurring skin or ear infections especially, investigating the underlying cause (allergies, anatomical issues, immune conditions) often matters more than finding the perfect antibiotic.
No — and this matters more than it sounds. Using leftover antibiotics means you don’t know whether the current illness is bacterial (amoxicillin won’t help a viral or fungal infection), whether the same bacteria is involved, or whether the dose and duration are appropriate for this infection. Beyond that, using medication without a current veterinary prescription means no one has examined your dog to confirm the diagnosis. What looks like a UTI could be bladder stones, a mass, or a condition requiring a completely different approach. The cost of a vet visit and a fresh prescription is worth knowing you’re treating the right thing the right way. Dispose of unused antibiotics properly — many pharmacies accept unused medications for safe disposal.
Amoxicillin is primarily cleared by the kidneys, so dogs with significant kidney disease may need dose adjustment or more careful monitoring during treatment. Liver disease is generally less of a concern with amoxicillin specifically, but any dog with organ compromise needs a full medication review before starting antibiotics. Your vet needs to know about your dog’s kidney and liver status before prescribing — which is why pre-treatment bloodwork is commonly recommended for senior dogs or those with known organ disease. Don’t withhold this information assuming the antibiotic is safe; dose adjustments exist precisely to handle these situations safely.
Amoxicillin is already one of the most affordable antibiotics your vet can prescribe. A full 7-day course for a medium-sized dog typically runs $15 to $30 at a veterinary or online pharmacy. With a valid prescription from your vet, you can fill amoxicillin at any human pharmacy — including large chains and discount programs — often at identical or lower cost per tablet, since the active ingredient is the same molecule used in people. The key difference to watch for is the inactive ingredients — confirm with your pharmacist that the human formulation does not contain xylitol, especially in any liquid form. Ask your vet to write the prescription as a written script so you have the flexibility to price-compare pharmacies.
Give the missed dose as soon as you realize it — unless the next scheduled dose is coming up within a few hours. In that case, skip the missed dose entirely and resume the regular schedule with the next dose. Never double-dose to make up for a missed one. Doubling a dose increases the risk of gastrointestinal side effects without meaningfully improving antibiotic effectiveness, since amoxicillin works by maintaining a minimum level in the bloodstream over time, not by delivering surges.
Not legally in the United States — amoxicillin requires a valid veterinary prescription (VCPR — veterinary-client-patient relationship). Online pharmacies require a written prescription from your vet before dispensing. You may see “fish amoxicillin” or similar products sold without a prescription, but these are unregulated, are not labeled for vertebrate medicine, frequently contain incorrect or inconsistent doses, and using them without a diagnosis is potentially harmful. Telehealth veterinary services can provide a prescription after a virtual consultation in states where this is legally permitted. Ask your vet whether their practice offers this option.
For susceptible infections, clinical improvement typically begins within 24 to 48 hours of starting amoxicillin. You might notice your dog seems more comfortable, eating better, or showing reduced signs of the infection (less straining to urinate, fewer skin scratching episodes, lower fever). Full resolution of all visible symptoms may take three to five days. If there is no noticeable improvement after three to four days, contact your vet — the FDA label recommends reviewing the diagnosis and changing therapy if no improvement is seen by day five. Waiting out a full course hoping for a late response is not the right approach when there’s no early sign of progress.
Yes — like all antibiotics, amoxicillin disrupts the normal gut microbiome as it works against the target infection. This is what causes the loose stools and diarrhea some dogs experience. Veterinary probiotics given during and for two to four weeks after a course of antibiotics can help restore healthy gut bacteria and reduce gastrointestinal side effects. Use canine-specific probiotic strains (Lactobacillus acidophilus, Bifidobacterium animalis) rather than human probiotics, which contain different strains at doses not calibrated for dogs. Give probiotics at least two hours apart from the amoxicillin dose — giving them simultaneously blunts the probiotic benefit.
Yes — amoxicillin can interfere with urine glucose testing using Clinitest-style copper reduction tests, causing false-positive results. If your dog is being monitored for diabetes and you need to test urine glucose during an amoxicillin course, alert your vet and use a glucose-oxidase based test instead. This interaction is well-documented in the veterinary literature and is one of the reasons vets need to know about all current medications, including antibiotics, before interpreting lab results.
It depends on the situation, and your vet is making a judgment call that’s worth understanding. For a first-time, straightforward infection in an otherwise healthy dog, empirical treatment with amoxicillin (prescribing without a culture, based on the most likely bacteria) is standard practice and entirely reasonable. Cultures are most valuable for: recurring infections that have failed at least one antibiotic course, deep infections like bone or prostate, infections in immunocompromised dogs, and any infection where the bacteria isn’t responding as expected. A culture takes 3 to 7 days to return results and adds cost — but it’s the only way to know with certainty which antibiotic will work and which won’t. In chronic or complicated cases, it’s often more cost-effective to culture once than to cycle through multiple failed antibiotic courses.
This page is for general informational and educational purposes only and does not constitute veterinary advice or a substitute for professional veterinary care. Amoxicillin is a prescription medication — never administer it to your dog without a current prescription from a licensed veterinarian. The dosage calculator on this page produces educational estimates based on the FDA-approved Amoxi-Tabs reference label (NADA #055-078, Zoetis Inc.) and is not a substitute for your veterinarian’s prescribed dose. Dosing, duration, and safety depend on factors only your vet can evaluate. If you suspect a drug overdose, contact the ASPCA Animal Poison Control Center at (888) 426-4435 or the Pet Poison Helpline at (855) 764-7661. To report adverse drug events in animals, contact the FDA at 1-888-FDA-VETS or fda.gov/reportanimalae. Prescription savings and pricing information is approximate and subject to change.