Penicillin G for Cow: Uses, Dosing & Side Effects

This information is for educational purposes only. Never give your pet any medication without your veterinarian's guidance. Dosing, frequency, and safety depend on your pet's specific health profile.

Penicillin G is an injectable antibiotic used in cattle to treat certain bacterial infections caused by organisms that are likely to respond to penicillin. In practice, the product most cattle operations use is procaine penicillin G injectable suspension, a long-acting form given by injection into the muscle. It is not useful for viral disease, and it will not be the right choice for every respiratory, uterine, foot, or wound problem.

For cows, this medication matters for two reasons. First, it can be effective and widely available when the infection is truly penicillin-susceptible. Second, cattle are food animals, so meat and milk withdrawal times are a major part of safe use. Your vet will match the drug, dose, route, and duration to the diagnosis, the animal's age and production class, and whether the cow is producing milk for people.

Penicillin G products are often sold over the counter in some settings, but that does not make them risk-free. Injection-site damage, allergic reactions, treatment failure, and illegal residues can all happen when the wrong dose, route, or duration is used. For that reason, Spectrum of Care still starts with the same advice: involve your vet early, especially if the cow is depressed, off feed, breathing hard, or not improving within 24 to 48 hours.

In U.S. cattle labeling, procaine penicillin G is commonly used for bacterial pneumonia caused by penicillin-susceptible organisms. In real-world herd medicine, your vet may also consider it for selected susceptible infections involving the skin, soft tissue, uterus, joints, navel, or feet when the likely bacteria and tissue penetration make penicillin a reasonable option.

That said, not every infection in a cow is a good penicillin case. Many respiratory infections involve bacteria where other antibiotics may be more practical, better studied for that site, or legally preferred based on the label and stewardship goals. Some conditions that look infectious are actually viral, metabolic, traumatic, or inflammatory, so an antibiotic alone may not help.

Your vet may recommend culture and susceptibility testing in valuable animals, repeat cases, herd outbreaks, or infections that are deep, severe, or slow to respond. That approach can help avoid wasted treatment days and can support better antimicrobial stewardship. In food animals, it also helps your vet choose a plan that balances animal welfare, residue avoidance, and practical farm management.

For labeled procaine penicillin G injectable suspension products in cattle, the common label dose is 3,000 units per pound of body weight, which equals 1 mL per 100 lb, given intramuscularly every 24 hours. Treatment is usually continued until recovery is apparent and for at least one day after signs improve, but labeled treatment should not exceed 4 consecutive days unless your vet directs otherwise. No more than 10 mL per injection site should be given, and sites should be rotated.

Veterinary references also list higher procaine penicillin G doses in cattle, such as 22,000 to 66,000 units/kg IM or SC every 24 hours, but doses above the labeled cattle dose are considered extra-label drug use in the U.S. For food animals, that requires a valid veterinarian-client-patient relationship, a clear medical rationale, and a vet-assigned extended withdrawal interval. Your vet may also choose a different route, interval, or antibiotic entirely depending on the disease site and severity.

This is one medication where estimating weight matters. Underdosing can lead to treatment failure and resistance pressure, while overdosing can increase residue risk and injection-site damage. Label information for common products states that milk from treated dairy cattle must be withheld for 48 hours after the last treatment, cattle must not be slaughtered for 14 days after the last treatment, and the product should not be used in calves to be processed for veal because a withdrawal period has not been established for pre-ruminating calves.

If a cow is not clearly improving within 24 to 48 hours, your vet should reassess the diagnosis and treatment plan. That may mean changing the antibiotic, adding supportive care, draining an abscess, treating pain and inflammation, or looking for a non-bacterial cause.

The most common side effects are pain or stinging at the injection site and a local tissue reaction where the drug was given. In cattle, label information warns that injection-site reactions can persist beyond the withdrawal period and may lead to trim loss at slaughter. Mild digestive upset can also occur, including reduced appetite or loose manure.

The most important serious risk is an allergic or anaphylactic reaction. This can happen unpredictably in animals sensitive to penicillin or procaine and may be fatal. Warning signs include sudden swelling, hives, weakness, collapse, or trouble breathing. See your vet immediately if any of these happen after an injection.

Call your vet promptly if your cow seems more depressed after treatment, develops severe diarrhea, shows worsening respiratory signs, or fails to improve within 1 to 2 days. Those changes can mean the infection is not susceptible, the diagnosis is incomplete, or the cow needs a different level of care. In food animals, side effects also include a practical concern: using the wrong dose, route, duration, or injection volume can create illegal meat or milk residues.

Penicillin G can interact with other medications, so your vet should know everything the cow has received recently, including antibiotics, anti-inflammatories, intramammary products, supplements, and medicated feeds. In general pharmacology, penicillins may work less predictably when combined with some bacteriostatic antibiotics because those drugs can slow bacterial growth that penicillin depends on for best effect.

The biggest real-world interaction issue in cattle is often not a classic drug-drug interaction. It is the combination of penicillin with extra-label dosing, multiple products, or incomplete records, which can complicate withdrawal times and residue prevention. If your vet uses penicillin in an extra-label way, federal rules require a medically justified plan, careful records, and a substantially extended withdrawal interval.

Tell your vet if the cow has had a prior reaction to penicillin, procaine, or another injectable antibiotic. Also mention whether she is lactating, close to slaughter, or intended for veal production, because those details directly affect whether penicillin is an appropriate option and how treatment should be documented.