Doramectin 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.

Doramectin is a macrocyclic lactone antiparasiticide used in cattle to treat a broad range of internal and external parasites. It is sold in injectable and topical cattle formulations under brand names such as Dectomax, with generic products also available. In cattle, the injectable product contains 10 mg/mL doramectin and is labeled at 200 mcg/kg, while topical cattle products are labeled at 500 mcg/kg.

This medication works by disrupting nerve and muscle function in susceptible parasites, leading to paralysis and death of the parasite. In mammals, the drug has a wider safety margin when used correctly, but it still needs careful dosing and handling. Your vet may choose doramectin as part of a herd parasite-control plan rather than as a stand-alone deworming decision.

For food animals, label restrictions matter. Injectable doramectin products for cattle carry a 35-day meat withdrawal, are not for use in female dairy cattle 20 months of age or older, and should not be used in calves to be processed for veal because a withdrawal period has not been established for preruminating calves.

In oxen and other cattle, doramectin is commonly used to treat and control gastrointestinal roundworms, lungworms, eyeworms, kidneyworms, grubs, sucking lice, biting lice with topical products, and mange mites. Merck Veterinary Manual also notes labeled use of doramectin in cattle for sarcoptic mange, and pour-on doramectin is listed for chorioptic mange in cattle.

Injectable doramectin has also been shown to provide persistent activity against some parasites, including protection against reinfestation with Ostertagia ostertagi for up to 21 days on label. That longer activity can be useful in some herd settings, but it also means your vet should think carefully about timing, season, resistance pressure, and withdrawal planning.

As of September 30, 2025, the FDA also conditionally approved DECTOMAX-CA1 for cattle for the prevention and treatment of New World screwworm larval infestations and prevention of reinfestation for 21 days. That is a specific labeled use in cattle, not a general reason to use doramectin without veterinary guidance.

Doramectin dosing in oxen depends on the product formulation, body weight, parasite being targeted, and the animal's food-production status. For injectable cattle products, the labeled dose is 1 mL per 110 lb body weight by subcutaneous or intramuscular injection, which delivers 200 mcg/kg. Common label examples include 220 lb = 2 mL, 550 lb = 5 mL, and 1,100 lb = 10 mL.

For topical pour-on cattle products, FDA approval documents describe a labeled dose of 500 mcg/kg body weight. Because concentration and applicator directions vary by product, your vet should confirm the exact mL dose and route from the label you are using. Injectable and pour-on products are not interchangeable on a mL-for-mL basis.

Accurate weight matters. Underdosing can reduce effectiveness and may contribute to parasite resistance, while overdosing increases risk of adverse effects and residue problems. Your vet may recommend fecal testing, seasonal timing, or follow-up monitoring to see whether the treatment worked well in your herd.

Food-animal restrictions are a major part of dosing decisions. Injectable doramectin in cattle has a 35-day slaughter withdrawal. It is not for use in female dairy cattle 20 months of age or older, and it should not be used in calves intended for veal. Always ask your vet to confirm the correct withdrawal interval for the exact product and use.

Most cattle tolerate doramectin well when it is used at the labeled dose, but side effects and safety issues can still happen. Mild problems may include temporary injection-site soreness, brief stress with handling, or reduced appetite for a short period after treatment. If a pour-on is used, skin irritation can occasionally occur where the product was applied.

More important risks are often tied to timing and species restrictions rather than classic drug toxicity. Doramectin labels warn that the product should not be used in other animal species, because severe adverse reactions, including fatalities in dogs, may occur. In cattle, treatment for cattle grubs at the wrong stage can trigger serious host-parasite reactions. Labeling warns that killing Hypoderma lineatum near the gullet may cause bloat, and killing H. bovis in the vertebral canal may cause staggering or paralysis.

Call your vet promptly if an ox seems weak, bloated, uncoordinated, stops eating, develops marked swelling, or does not improve after treatment. Also contact your vet if parasites seem to persist, because treatment failure can reflect resistance, underdosing, reinfection, or the wrong parasite target.

Published cattle labels and FDA summaries for doramectin focus more on route, residue warnings, species restrictions, and parasite timing than on a long list of formal drug-drug interactions. Even so, your vet should review all medications, feed additives, and recent treatments before using doramectin, especially in food animals where residue compliance matters.

Caution is reasonable when doramectin is used alongside other macrocyclic lactones or antiparasitic products, because overlapping parasite coverage can complicate resistance management and may increase the chance of dosing errors. Your vet may also want to know about recent use of pour-ons, injectable dewormers, or combination parasite-control products so the herd plan stays coordinated.

The biggest practical interaction issue in cattle is often with the production system rather than another drug. Doramectin use can conflict with milk or slaughter plans because of withdrawal restrictions, and some formulations are not labeled for certain classes of cattle. If your ox is part of a working, breeding, or food-animal program, ask your vet to review the full treatment record before dosing.