Amoxicillin
Amoxicillin trihydrate
Also known as: Amoxil · Amoxi-Tabs · Amoxi-Drop · Amoxi-Mast · Trimox · Moxatag · Amoxibactin · Amoxycare · Amoxypen · Betamox · Bimoxyl · Clamoxyl · amoxycillin · p-hydroxyampicillin · BRL 2333
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Gram-positive infections | 10 mg/kg PO, IM, SC twice daily for at least 2 days after symptoms subside. | PO, IM, SC | q12h | At least 2 days after symptoms subside | 🌎 NA |
| Gram-negative infections | 20 mg/kg PO three times daily or IM, SC twice daily for at least 2 days after symptoms subside | PO, IM, SC | q8h (PO) or q12h (IM, SC) | At least 2 days after symptoms subside | 🌎 NA |
| Susceptible UTI's | 10-20 mg/kg PO q12h for 5-7 days. | PO | q12h | 5-7 days | 🌎 NA |
| Susceptible systemic infections (bacteremia/sepsis) | 22-30 mg/kg IV , IM, SC q8h for 7 days. | IV, IM, SC | q8h | 7 days | 🌎 NA |
| Susceptible orthopedic infections | 22-30 mg/kg IV , IM, SC, or PO q6-8h for 7-10 days. | IV, IM, SC, PO | q6-8h | 7-10 days | 🌎 NA |
| Lyme disease | 22 mg/kg PO q12h for 21-28 days | PO | q12h | 21-28 days | 🌎 NA |
| Susceptible urinary tract infections | 11 mg/kg PO q8h. | PO | q8h | — | 🌎 NA |
| Preventative therapy for repeated (>2 per 6 months) urinary tract Gram-positive bacterial infections | 20 mg/kg PO once daily before bedtime after the dog has urinated. | PO | q24h | — | 🌎 NA |
| Susceptible bacterial infections | 7 mg/kg | IM | q24h | — | 🌍 EU |
| Susceptible bacterial infections (depot preparations) | 15 mg/kg | IM | q48h | — | 🌍 EU |
| Susceptible bacterial infections | 10 mg/kg | PO | q8-12h | — | 🌍 EU |
| Bacterial cystitis | 11-15 mg/kg | PO | q8h | — | 🌍 EU |
- Preventative therapy for repeated (>2 per 6 months) urinary tract Gram-positive bacterial infections: Use only after effective treatment completed using full therapeutic doses.
- Susceptible bacterial infections (depot preparations): For depot preparations only
- Susceptible bacterial infections: Dose chosen will depend on site of infection, causal organism and severity of the disease.
- Bacterial cystitis: Evidence of a need for clavulanic acid is lacking even in infections with beta-lactamase producing bacteria.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Gram-positive infections | 10 mg/kg PO, IM, SC twice daily for at least 2 days after symptoms subside. | PO, IM, SC | q12h | At least 2 days after symptoms subside | 🌎 NA |
| Gram-negative infections | 20 mg/kg PO three times daily or IM, SC twice daily for at least 2 days after symptoms subside | PO, IM, SC | q8h (PO) or q12h (IM, SC) | At least 2 days after symptoms subside | 🌎 NA |
| Susceptible UTI's and soft tissue infections | 50 mg (total dose per cat) or 11-22 mg/kg PO once daily for 5-7 days. | PO | q24h | 5-7 days | 🌎 NA |
| Sepsis | 10-20 mg/kg IV , SC, or PO q12h for as long as necessary. | IV, SC, PO | q12h | As long as necessary | 🌎 NA |
| C. perfringens, bacterial overgrowth (GI) | 22 mg/kg PO once daily for 5 days | PO | q24h | 5 days | 🌎 NA |
| C. perfringens enterotoxicosis | 11-22 mg/kg PO two to three times daily for 7 days | PO | q8-12h | 7 days | 🌎 NA |
| H. pylori infections (triple therapy) | amoxicillin 20 mg/kg PO twice daily for 14 days; metronidazole 10-15 mg/kg PO twice daily; clarithromycin 7.5 mg/kg PO twice daily | PO | q12h | 14 days | 🌎 NA |
| Susceptible bacterial infections | 7 mg/kg | IM | q24h | — | 🌍 EU |
| Susceptible bacterial infections (depot preparations) | 15 mg/kg | IM | q48h | — | 🌍 EU |
| Susceptible bacterial infections | 10 mg/kg | PO | q8-12h | — | 🌍 EU |
| Bacterial cystitis | 11-15 mg/kg | PO | q8h | — | 🌍 EU |
- Sepsis: Generally treat for at least 2 days after all signs of infection are gone.
- H. pylori infections (triple therapy): Used in combination with metronidazole and clarithromycin.
- Susceptible bacterial infections (depot preparations): For depot preparations only
- Susceptible bacterial infections: Dose chosen will depend on site of infection, causal organism and severity of the disease.
- Bacterial cystitis: Evidence of a need for clavulanic acid is lacking even in infections with beta-lactamase producing bacteria.
Small Mammals
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Susceptible infections (Hedgehogs) | 15 mg/kg IM or PO q12h | IM, PO | q12h | — | 🌎 NA |
- Susceptible infections (Hedgehogs): See contraindications regarding use in rabbits/rodents.
Ferrets
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Eliminating Helicobacter gastritis infections (triple therapy) | Metronidazole 22 mg/kg, amoxicillin 22 mg/kg and bismuth subsalicylate (original Pepto-Bismol ®) 17.6 mg/kg PO. Give each 3 times daily for 3-4 weeks. | PO | q8h | 3-4 weeks | 🌎 NA |
| Eliminating Helicobacter gastritis infections (triple therapy) | Metronidazole 20 mg/kg PO q12h, amoxicillin 20 mg/kg PO q12h and bismuth subsalicylate 17.5 mg/kg PO q8h. Give 21 days. | PO | q12h | 21 days | 🌎 NA |
| Susceptible infections | 10-35 mg/kg PO or SC twice daily | PO, SC | q12h | — | 🌎 NA |
- Eliminating Helicobacter gastritis infections (triple therapy): Sucralfate and famotidine are also used. Fluids and assisted feeding should be continued.
Birds
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Susceptible infections | 125 mg/kg q12h PO. Mix oral solution to double strength to a final concentration of 125 mg/mL. | PO | q12h | — | 🌎 NA |
| Susceptible infections | 100 mg/kg q8h, IM, SC, PO | IM, SC, PO | q8h | — | 🌎 NA |
| Susceptible infections (Ratites) | 15-22 mg/kg PO twice daily; in drinking water: 250 mg/gallon for 3-5 days | PO, drinking water | q12h / continuous | 3-5 days | 🌎 NA |
Reptiles
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Susceptible infections (all species) | 22 mg/kg PO q12-24h | PO | q12-24h | — | 🌎 NA |
- Susceptible infections (all species): Not very useful unless used in combination with aminoglycosides
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Respiratory infections | 20-30 mg/kg PO q6h | PO | q6h | — | 🌎 NA |
| Susceptible infections (Foals - Amoxicillin Sodium) | 15-30 mg/kg IV or IM q6-8h | IV, IM | q6-8h | — | 🌎 NA |
| Susceptible infections (Foals - Amoxicillin trihydrate suspension) | 25-40 mg/kg PO q8h | PO | q8h | — | 🌎 NA |
| Susceptible infections (Foals - Amoxicillin/clavulanate) | 15-25 mg/kg IV q6-8h | IV | q6-8h | — | 🌎 NA |
Cattle
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Susceptible infections | 6-10 mg/kg SC or IM q24h | SC, IM | q24h | — | 🌎 NA |
| Respiratory infections | 11 mg/kg IM or SC q12h | IM, SC | q12h | — | 🌎 NA |
| Susceptible infections (Calves - Amoxicillin trihydrate) | 7 mg/kg PO q8-12h | PO | q8-12h | — | 🌎 NA |
- Susceptible infections: Withdrawal time = 30 days
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Amoxicillin is a widely prescribed, broad-spectrum aminopenicillin antibiotic used in veterinary medicine to treat a variety of bacterial infections.
Key pharmacological features include:
- Spectrum of Activity: Effective against many Gram-positive aerobes, some Gram-negative aerobes (e.g., E. coli, Klebsiella, Haemophilus), and many obligate anaerobes (including Clostridium spp.).
- Beta-Lactamase Susceptibility: Like ampicillin, it is inactivated by beta-lactamase-producing bacteria (e.g., Staphylococcus aureus). It is often combined with clavulanate to overcome this resistance.
- Clinical Utility: It is considered a first-line empiric choice for feline abscesses, susceptible urinary tract infections (UTIs), and soft tissue infections.
- Pharmacokinetic Advantage: Compared to ampicillin, amoxicillin has significantly better oral bioavailability in monogastric animals, achieving serum levels 1.5 to 3 times higher at equivalent doses.
Mechanism of action
Amoxicillin is a time-dependent, bactericidal antibiotic that disrupts bacterial cell wall synthesis.
- Mechanism: The beta-lactam ring mimics the D-alanyl-D-alanine terminal of the peptidoglycan precursor.
- Pathway: Amoxicillin binds to specific penicillin-binding proteins (PBPs) (such as transpeptidases, carboxypeptidases, and endopeptidases) located on the inner surface of the bacterial cell membrane → inhibits the cross-linking of mucopeptide (peptidoglycan) chains → compromises the structural integrity of the cell wall → creates an osmotically unstable spheroplast → results in cell lysis and death.
- Efficacy: It is most effective against actively dividing and growing bacteria.
Safety & warnings
Contraindications
- Patients with a history of hypersensitivity to penicillins
- Oral administration in hindgut fermenters (rabbits, guinea pigs, chinchillas, hamsters) due to risk of fatal clostridial enterotoxemia
- Oral administration in patients with septicemia, shock, or grave illness (due to delayed/diminished GI absorption)
Adverse effects
- Gastrointestinal upset (anorexia, vomiting, diarrhea)
- Antibiotic-associated diarrhea and gut flora alteration
- Hypersensitivity reactions (rashes, fever, anaphylaxis)
- Eosinophilia, neutropenia, agranulocytosis, thrombocytopenia, leukopenia, anemias
- Lymphadenopathy
- Neurotoxicity (e.g., ataxia) at very high doses or prolonged use
- Elevated liver enzymes (rare)
- Tachypnea, dyspnea, edema, and tachycardia (reported in dogs)
Precautions
Species Warning: Never administer amoxicillin (or other penicillins) orally to rabbits, guinea pigs, chinchillas, or hamsters, as it can cause severe, often fatal, clostridial enterotoxemia.
- Cross-Reactivity: Use with caution in patients with documented hypersensitivity to other beta-lactam antibiotics (e.g., cephalosporins, carbapenems).
- Pregnancy: Crosses the placenta. Categorized as FDA Category B (human) and Class A (veterinary - probably safe), but should be used only when potential benefits outweigh risks.
- Laboratory Tests: May cause false-positive urine glucose determinations when using cupric sulfate solutions (e.g., Clinitest).
Drug interactions
Potential in vitro antagonism; concurrent use has historically been discouraged, though clinical significance is debated.
Amoxicillin may decrease the renal excretion of methotrexate, leading to increased levels and potential toxicity.
Competitively blocks the tubular secretion of penicillins, increasing serum levels and prolonging serum half-life.
In vitro inactivation of aminoglycosides by beta-lactams; may falsely decrease aminoglycoside serum concentrations if samples are stored prior to analysis.
Potential antagonism of bactericidal activity (bacteriostatic vs bactericidal)
Potential antagonism of bactericidal activity
Potential antagonism of bactericidal activity
Inactivation of aminoglycoside if mixed in the same syringe
Synergistic antimicrobial effect when used concurrently
Monitoring
- Clinical efficacy (resolution of infection signs)
- Adverse effects (GI upset, signs of hypersensitivity)
Pharmacokinetics
Half-life
Absorption
Relatively stable in gastric acid. About 74-92% absorbed orally in monogastric animals. Food decreases the rate but not the extent of absorption. Serum levels are generally 1.5-3 times greater than ampicillin after equivalent oral doses.
Distribution
Volume of distribution is ~0.2 L/kg in dogs. Widely distributed to tissues including liver, lungs, muscle, bile, and ascitic/pleural/synovial fluids. Crosses into CSF when meninges are inflamed (10-60% of serum levels). Crosses the placenta. Protein binding is ~13% in dogs.
Metabolism
Some of the drug is metabolized by hydrolysis to inactive penicilloic acids.
Elimination
Eliminated primarily through renal mechanisms, principally by tubular secretion. Clearance is reportedly 1.9 mL/kg/min in dogs.
Overdose
Acute oral penicillin overdoses are unlikely to cause significant problems other than gastrointestinal distress (vomiting, diarrhea, anorexia).
In humans, very high dosages of parenteral penicillins, especially in patients with compromised renal function, have induced CNS effects (e.g., seizures, ataxia). Treatment is generally supportive and symptomatic.
Available products
Formulations
- Oral tablets
- Oral chewable tablets
- Oral capsules
- Powder for oral suspension
- Intramammary infusion
Veterinary
- Amoxicillin Oral Tablets: 50 mg, 100 mg, 150 mg, 200 mg, & 400 mg (Amoxi-Tabs®)
- Amoxicillin Powder for Oral Suspension: 50 mg/mL after reconstitution (Amoxi-Drop®)
- Amoxicillin Intramammary Infusion: 62.5 mg/syringe (Amoxi-Mast®)
Human-labeled
- Amoxicillin Oral Tablets (chewable): 125 mg, 200 mg, 250 mg, & 400 mg (Amoxil®)
- Amoxicillin Oral Tablets: 500 mg & 875 mg (Amoxil®)
- Amoxicillin Oral Capsules: 250 mg & 500 mg (Amoxil®)
- Amoxicillin Powder for Oral Suspension: 200 mg/5 mL, 250 mg/5 mL, 400 mg/5 mL (Amoxil®, Trimox®)
- Amoxicillin Oral Extended-Release Tablets: 775 mg (Moxatag®)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Capsules, tablets, and powder for oral suspension should be stored at room temperature (15-30°C) in tight containers. After reconstitution, the oral suspension should preferably be refrigerated (though not absolutely necessary) and any unused product discarded after 14 days.
Client information
- Administration: Amoxicillin can be given with or without food. However, if your pet experiences stomach upset (vomiting or loss of appetite), giving the medication with a meal may help.
- Storage: If you are using the liquid oral suspension, it is best to keep it refrigerated, though room temperature is acceptable. Discard any unused liquid after 14 days.
- Completion of Therapy: Always finish the entire prescription as directed by your veterinarian, even if your pet seems completely better. Stopping early can lead to resistant bacterial infections.
- Side Effects: Mild diarrhea or vomiting can occur. If these symptoms become severe, or if you notice signs of an allergic reaction (like facial swelling, hives, or difficulty breathing), contact your veterinarian immediately.
- Species Warning: Never share this medication with small pets like rabbits, guinea pigs, or hamsters, as it can be fatal to them.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.