Terramycin is a veterinary antibiotic ointment used to treat bacterial infections in animals, including cats, dogs, cattle, sheep, and horses. Despite its long history and familiar name, the Terramycin brand sold today is labeled “For Animal Use Only” and is not approved for human use in the United States.
What Terramycin Contains
Terramycin combines two antibiotics: oxytetracycline and polymyxin B sulfate, blended into a petroleum-based ointment. Each gram contains 5 mg of oxytetracycline and 10,000 units of polymyxin B. The two antibiotics work against different types of bacteria, giving the ointment a broader range of coverage than either ingredient alone.
Oxytetracycline belongs to the tetracycline class of antibiotics. It stops bacteria from growing by blocking a critical step in protein production inside bacterial cells. The drug slips easily through bacterial membranes, attaches to part of the cell’s protein-building machinery, and prevents bacteria from assembling the proteins they need to multiply. This effect is reversible, meaning the drug slows and stops bacterial growth rather than directly killing cells outright.
Primary Veterinary Uses
The most widely recognized form of Terramycin is the ophthalmic (eye) ointment, manufactured by Zoetis, a major animal health company. It comes in a small 3.5-gram tube and is applied directly to the eye two to four times daily to treat bacterial eye infections in animals. Pet owners commonly use it for conjunctivitis (pink eye) and other surface eye infections in dogs and cats. Livestock producers rely on it for similar eye infections in cattle and horses, where conditions like pinkeye can spread quickly through a herd.
Beyond the eye ointment, oxytetracycline itself has a much wider footprint in veterinary medicine. Injectable forms and soluble powders are used in livestock for respiratory infections, foot rot, wound infections, and other bacterial diseases. In agriculture, oxytetracycline is also sprayed on crops. Peach orchards in the southeastern United States, for example, are sometimes treated almost weekly with oxytetracycline during spring and summer to manage bacterial spot disease.
Why It’s Not for Human Use
Older readers may remember a time when oxytetracycline-based products were prescribed for people. Oxytetracycline was one of the early tetracycline antibiotics discovered in the late 1940s, and it saw widespread human use for decades. Today, however, the Terramycin brand ophthalmic ointment is explicitly labeled “Not for Human Use.” Human medicine has largely moved on to newer antibiotics with better dosing profiles and fewer issues. If you have an eye infection, your doctor will prescribe a different antibiotic ointment or drop formulated and approved for people.
This distinction matters because Terramycin is easy to find at farm supply stores and online pet retailers without a prescription in many states. Some people purchase it for themselves, particularly for eye infections, assuming an antibiotic is an antibiotic. Veterinary formulations aren’t held to the same manufacturing standards as human pharmaceuticals, and using them bypasses the diagnostic step that determines whether an antibiotic is even the right treatment for your particular infection.
How It’s Applied in Animals
For eye infections, the ointment is squeezed in a thin strip directly onto the surface of the animal’s eye or inside the lower eyelid. The standard recommendation is two to four applications per day. The prescribing information does not specify a fixed treatment duration, so veterinarians typically advise continuing for a set number of days based on the severity of the infection and how quickly symptoms improve.
Because the ointment has a thick, petroleum-like base, it stays in contact with the eye longer than liquid drops would. This is especially practical for livestock and outdoor animals where frequent reapplication is difficult. The tradeoff is temporary blurred vision and a greasy residue, which most animals tolerate well.
Growing Resistance Concerns
Like all antibiotics, oxytetracycline faces the problem of bacterial resistance. Heavy, repeated use gives bacteria opportunities to develop defenses against the drug. Researchers studying peach orchards in South Carolina found oxytetracycline-resistant bacteria appearing despite intensive spray programs, sometimes with weekly applications at 150 parts per million. In some of these resistant strains, the genes conferring resistance sat on small, mobile pieces of DNA (plasmids) that could transfer to other bacterial species, potentially spreading resistance beyond the original target pathogen.
In veterinary settings, resistance trends vary by region and by the type of infection being treated. Oxytetracycline remains effective for many common animal infections, but veterinarians increasingly rely on bacterial culture and sensitivity testing before prescribing it for stubborn or recurring cases. Using Terramycin only when truly needed, and completing the full course of treatment, helps preserve its effectiveness.
What to Expect When Using It for Pets
If your veterinarian recommends Terramycin ophthalmic ointment for your dog or cat, the process is straightforward. You’ll gently pull down the lower eyelid, apply a small ribbon of ointment along the inner lid, and let the animal blink to distribute it. Most pets resist the first few applications but adjust quickly. You may notice the eye looking slightly glossy or filmy afterward, which is normal.
Mild irritation at the application site is the most common issue. If you notice increased redness, swelling, or discharge that worsens rather than improves over the first couple of days, contact your veterinarian. Some infections require a different antibiotic, and eye conditions that don’t respond promptly can lead to more serious damage if left on the wrong treatment.