Gamithromycin for Ox: 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.

Gamithromycin is a prescription macrolide antibiotic used in cattle medicine. In the U.S., it is sold under brand names including Zactran and the FDA-approved generic Gamrozyne. It is labeled for beef cattle and non-lactating dairy cattle and is given as a single subcutaneous injection in the neck under your vet's direction.

This drug is designed to concentrate well in lung tissue, which is why your vet may consider it when an ox has signs of bovine respiratory disease (BRD). BRD is a broad term for pneumonia and related respiratory infections in cattle, often involving stress, transport, crowding, weather shifts, and bacterial infection.

Gamithromycin is not a routine at-home medication for pet parents to use without veterinary oversight. In food animals, treatment decisions also have to account for withdrawal times, legal drug use, and herd-level disease management. Your vet will weigh whether this antibiotic fits the animal, the diagnosis, and the production goals.

In U.S. cattle, gamithromycin is labeled for the treatment of BRD associated with Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, and Mycoplasma bovis. It is also labeled for the control of respiratory disease in beef and non-lactating dairy cattle that are considered high risk for developing BRD.

That means your vet may use it in two different ways. One is treatment, when an ox is already sick and showing signs such as fever, depression, nasal discharge, cough, or increased breathing effort. The other is metaphylaxis/control, when a group of cattle has a meaningful risk of BRD after events like shipping or commingling, and your vet decides a preventive group strategy is appropriate.

Gamithromycin is not a cure-all for every cough or fever. Respiratory signs can also be caused by viruses, parasites, aspiration, or noninfectious problems. Your vet may recommend an exam, temperature check, lung assessment, and sometimes testing before choosing this medication.

The labeled U.S. dose for cattle is 6 mg/kg once, which equals 2 mL per 110 lb body weight as a subcutaneous injection in the neck. If the total volume is more than 10 mL, it should be split so that no more than 10 mL is given at one injection site. Accurate body weight matters because underdosing can reduce effectiveness and may contribute to antimicrobial resistance.

For a practical example, a 550 lb ox would receive 10 mL total. A 1,100 lb ox would receive 20 mL total, divided across at least 2 neck injection sites. This medication is typically given as a one-time dose, not a daily series, unless your vet directs a different plan based on a specific legal and medical context.

In U.S. labeling, gamithromycin is for beef and non-lactating dairy cattle. It carries a 35-day meat withdrawal time. It is not for use in animals producing milk for human consumption, and your vet should guide any use decisions in breeding or dairy animals. Because this is a prescription antimicrobial in a food animal, do not guess on dose, route, or timing.

The most common side effect reported with gamithromycin in cattle is a temporary injection-site reaction. You may notice a visible swelling or firmness where the shot was given, and some animals show mild, short-lived discomfort. In European product information, these swellings are described as very common, usually resolving within 3 to 14 days, though some can persist longer.

In U.S. labeling summaries, local tissue reactions are also noted and may lead to trim loss of edible tissue at slaughter. That matters in food animals even when the ox otherwise seems comfortable. Mild soreness, brief head turning, or restlessness around the time of injection can happen.

Serious reactions appear to be uncommon, but any animal that becomes weak, collapses, has marked breathing trouble, or worsens after treatment needs urgent veterinary attention. Also contact your vet if fever, cough, appetite loss, or labored breathing are not improving as expected, because the diagnosis may need to be revisited.

Gamithromycin is a macrolide antibiotic, and product information warns against using it at the same time as other macrolides or lincosamides. These drugs can overlap in how they work, and combining them may not improve results. It can also complicate antimicrobial stewardship decisions for your herd.

Cross-resistance may occur with other macrolides. In practical terms, if bacteria on your farm have reduced susceptibility to one macrolide, another drug in the same class may also work less well. That is one reason your vet may consider treatment history, recent antibiotic exposure, culture data, or herd response patterns before choosing gamithromycin.

Be sure your vet knows about every product the ox has recently received, including other antibiotics, anti-inflammatories, vaccines, and feed-through medications. In food animals, timing, route, and recordkeeping all matter. Your vet can help you avoid combinations that are unnecessary, conflicting, or harder to defend from a residue and stewardship standpoint.