Penicillin V Potassium
Phenoxymethylpenicillin potassium
Also known as: Veetids · fenoximetilpenicilina · penicillin phenoxymethyl · phenomycilline · phenoxymethylpenicillinum
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 |
|---|---|---|---|---|---|
| Susceptible infections | 5.5-11 mg/kg | PO | q6-8h | — | 🌎 NA |
| Soft tissue infections | 10 mg/kg | PO | q8h | 7 days | 🌎 NA |
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Susceptible infections | 5.5-11 mg/kg | PO | q6-8h | — | 🌎 NA |
| Soft tissue infections | 10 mg/kg | PO | q8h | 7 days | 🌎 NA |
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Susceptible infections | 110,000 U/kg (68.75 mg/kg) | PO | q8h | — | 🌎 NA |
| Susceptible infections | 110,000 U/kg | PO | q6-12h | — | 🌎 NA |
- Susceptible infections: May yield supra-optimal levels against uncomplicated infections by sensitive organisms
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Penicillin V Potassium is a natural, narrow-spectrum beta-lactam antibiotic.
Key characteristics include:
- Spectrum of Activity: Highly effective against most gram-positive aerobic and anaerobic cocci, spirochetes, and some gram-positive bacilli (e.g., Bacillus anthracis, Clostridium spp., Actinomyces).
- Limitations: It is generally inactive against penicillinase-producing strains (like many Staphylococcus spp.), most gram-negative bacilli, Rickettsia, Mycoplasma, and fungi.
- Clinical Utility: While slightly less active in vitro than Penicillin G, Penicillin V is significantly more resistant to stomach acid. This superior oral bioavailability makes it the preferred natural penicillin for mild to moderately severe susceptible infections in monogastric animals when oral dosing is required.
Clinical Pearl: Because of increasing resistance patterns, natural penicillins are often reserved for specific susceptible infections (like certain oral/dental infections or specific clostridial diseases) rather than empiric broad-spectrum therapy.
Mechanism of action
Penicillin V is a time-dependent, bactericidal antibiotic.
It works by targeting the bacterial cell wall:
- Binds to specific penicillin-binding proteins (PBPs) (such as transpeptidases and carboxypeptidases) located inside the bacterial cytoplasmic membrane.
- Inhibits the third and final stage of bacterial cell wall synthesis by preventing the cross-linking of peptidoglycan strands.
- This leads to a defective, osmotically unstable cell wall (spheroplast) → cell lysis and death.
Note: Like all beta-lactams, it is only effective against actively growing and dividing bacteria.
Safety & warnings
Contraindications
- Known hypersensitivity to penicillins
- Oral administration in patients with septicemia, shock, or grave illness (due to delayed/diminished GI absorption)
- Use in sensitive species (snakes, birds, turtles, guinea pigs, chinchillas) without extreme caution
Adverse effects
- GI effects (anorexia, vomiting, diarrhea)
- Hypersensitivity reactions (rashes, fever, eosinophilia, anaphylaxis)
- Antibiotic-associated diarrhea and superinfections (due to altered gut flora)
- Neurotoxicity (e.g., ataxia in dogs) at very high doses
- Elevated liver enzymes
- Tachypnea, dyspnea, edema, and tachycardia (reported in dogs)
Precautions
Use with caution in patients with documented hypersensitivity to other beta-lactam antibiotics (e.g., cephalosporins, carbapenems) due to potential cross-reactivity. High doses of potassium salts can cause electrolyte imbalances, particularly in small animals with preexisting renal disease, congestive heart failure, or electrolyte abnormalities. Safe use during pregnancy is not firmly established (FDA Category B), and it is excreted in maternal milk, which could cause diarrhea or candidiasis in nursing offspring.
Drug interactions
In vitro synergism against certain bacteria; however, mixing them in the same syringe or fluid line can cause physical inactivation of the aminoglycoside.
May antagonize the bactericidal activity of penicillins, which require actively dividing bacteria to be effective.
Penicillins may decrease the renal elimination of methotrexate, potentially increasing its toxicity.
Competitively blocks the renal tubular secretion of penicillins, significantly increasing their serum levels and half-lives.
Monitoring
- Clinical efficacy (resolution of infection signs)
- Adverse GI effects
- Signs of hypersensitivity or allergic reaction
Pharmacokinetics
Half-life
Absorption
Significantly more resistant to acid-catalyzed inactivation in the gut compared to Penicillin G. Oral bioavailability is 60-73% in humans, but only 30% in calves. In dogs, food decreases the rate and extent of absorption.
Distribution
Distributes widely into tissues. Bound to plasma proteins to a larger extent than Penicillin G (approximately 80%). Crosses the placenta and is excreted in maternal milk.
Metabolism
Minimal hepatic metabolism.
Elimination
Excreted rapidly in the urine via the kidneys (tubular secretion and glomerular filtration).
Overdose
Acute oral overdoses are unlikely to cause significant problems other than gastrointestinal distress (vomiting, diarrhea). In humans, massive overdoses of parenteral penicillins (especially in patients with renal impairment) have induced CNS effects and seizures. Treatment is supportive.
Available products
Formulations
- Tablets
- Powder for oral solution
Human-labeled
- Penicillin V Potassium Tablets: 250 mg & 500 mg (Veetids, generic)
- Penicillin V Potassium Powder for Oral Solution: 25 mg/mL & 50 mg/mL in 100 mL & 200 mL (Veetids, generic)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Tablets and powder for oral solution should be stored in tight containers at room temperature (15-30°C). After reconstitution, the oral solution must be stored in the refrigerator (2-8°C) and any unused portion discarded after 14 days.
Client information
Giving the Medication
- Timing is important: Unless your veterinarian tells you otherwise, give this medication on an empty stomach (at least 1 hour before feeding or 2 hours after feeding) to ensure it is properly absorbed.
- Finish the prescription: Always give the antibiotic for the full length of time prescribed, even if your pet seems completely better. Stopping early can lead to resistant infections.
Storage
- If you were given a liquid suspension, keep it in the refrigerator.
- Throw away any unused liquid after 14 days.
What to Watch For
- Contact your veterinarian if your pet develops severe diarrhea, vomiting, loss of appetite, or signs of an allergic reaction (such as facial swelling, hives, or difficulty breathing).
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.