Doramectin for Pigs: 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 an injectable antiparasitic medication used in pigs to treat both internal worms and some external parasites. It belongs to the macrocyclic lactone family, sometimes called avermectins. In the U.S., the best-known swine product is Dectomax Injectable, a 1% solution containing 10 mg/mL of doramectin. It is labeled for intramuscular use in swine only and is formulated to deliver 300 mcg/kg when dosed at 1 mL per 75 lb body weight.

Doramectin works by disrupting nerve signaling in susceptible parasites, which leads to paralysis and death of the parasite. In pigs, it is labeled for treatment and control of several important parasites, including roundworms, lungworms, kidney worms, sarcoptic mange mites, and sucking lice. Because parasite control plans vary by age group, housing, and herd exposure, your vet may recommend doramectin as part of a broader herd health program rather than as a one-time fix.

For pet pigs and small hobby herds, this medication can be useful when parasites are confirmed or strongly suspected. Still, it is not a substitute for diagnosis. Skin disease, itching, poor growth, coughing, and weight loss can have many causes, so your vet may pair treatment with fecal testing, skin scrapings, or herd-level management changes.

In pigs, doramectin is labeled for treatment and control of gastrointestinal roundworms, lungworms, kidney worms, sarcoptic mange, and sucking lice. The swine label specifically includes parasites such as Ascaris suum, Oesophagostomum dentatum, Oesophagostomum quadrispinulatum, Strongyloides ransomi, Hyostrongylus rubidus, Metastrongylus spp., Stephanurus dentatus, Sarcoptes scabiei var. suis, and Haematopinus suis.

That broad coverage makes doramectin especially helpful when pigs have a mixed parasite burden. For example, a pig with itching and crusting from mange may also have internal parasites contributing to poor thrift or slower weight gain. In outdoor pigs, backyard pigs, and pigs with exposure to contaminated soil or new herd additions, your vet may consider doramectin as one option in a larger parasite-control plan.

Doramectin is also commonly discussed for miniature pet pigs. Merck lists 0.3 mg/kg IM, with a repeat dose in 10 to 14 days for sarcoptic mange, as a common approach in miniature pigs. Even so, pet pigs still need individualized guidance. Age, body condition, pregnancy status, intended food use, and the possibility of drug resistance all matter when your vet chooses a treatment plan.

For labeled swine use, doramectin is given at 300 mcg/kg (0.3 mg/kg) intramuscularly, which equals 1 mL per 75 lb body weight for the 1% injectable product. The injection is given in the neck muscle. The product label stresses accurate body weight and warns against underdosing, because low dosing can lead to treatment failure and may encourage parasite resistance.

Common label examples include 15 lb = 0.2 mL, 30 lb = 0.4 mL, 75 lb = 1.0 mL, 150 lb = 2.0 mL, 225 lb = 3.0 mL, and 300 lb = 4.0 mL. For piglets, the label recommends a tuberculin syringe for more accurate small-volume dosing. Your vet may also advise herd-timing strategies, such as treating sows 7 to 14 days before farrowing, gilts before breeding and before farrowing, boars at least twice yearly, and incoming feeder pigs before placement into clean quarters.

For sarcoptic mange, a second dose 10 to 14 days later is often used in practice and is commonly recommended in eradication-style programs. That repeat timing helps address mites that were not eliminated with the first treatment cycle. Your vet may also recommend treating all in-contact pigs and cleaning or rotating contaminated housing to reduce reinfestation.

If the pig may enter the food chain, withdrawal guidance matters. The current U.S. swine label states do not slaughter for human consumption within 24 days of treatment. Never change the route, concentration, or schedule on your own. Food-animal drug rules are strict, and your vet should guide any use decisions.

Doramectin is generally well tolerated in pigs when used according to label directions, but side effects can still happen. The most practical issues pet parents and producers notice are injection-site discomfort, brief soreness, or stress related to restraint and injection. In pigs with heavy parasite burdens, you may also see a short period where skin irritation or scratching seems slow to improve, especially with mange, because healing takes time even after mites are killed.

Call your vet promptly if your pig seems unusually weak, stops eating, has marked swelling at the injection site, develops severe lethargy, or shows worsening neurologic signs such as tremors, incoordination, or collapse. Those reactions are not expected in routine labeled use and deserve veterinary attention right away. If a pig has ongoing itching after treatment, that does not always mean the drug failed. Reinfestation, environmental contamination, secondary skin infection, or a different skin disease may be involved.

There are also important species-safety concerns around the product itself. The label warns that doramectin injectable is developed for cattle and swine only and should not be used in other species, because severe reactions, including fatalities in dogs, have been reported with avermectin exposure. The formulation also uses a sesame oil vehicle, which may matter if your vet is considering sensitivity or injection-site reactions.

Published swine-specific interaction data for doramectin are limited, so this is an area where your vet's judgment is especially important. In general, doramectin is part of the macrocyclic lactone group, so your vet will usually be cautious about combining it with other drugs in the same family, such as ivermectin or moxidectin, unless there is a clear reason and a defined plan. Stacking similar antiparasitic drugs can increase the risk of overdosing or confusing treatment response.

Your vet may also review all recent medications, supplements, and feed additives before treatment. That matters most in pigs that are young, debilitated, pregnant, underweight, or being treated for another illness at the same time. If a pig has already received another dewormer recently, your vet may want to confirm which parasites are present before repeating treatment.

For food animals, the biggest practical "interaction" issue is often not a classic drug-drug interaction but a regulatory and residue concern. Route, dose, and timing affect withdrawal planning. Tell your vet about every product the pig has received, including over-the-counter dewormers, injectable vitamins, and medicated feed, so they can build a safe and compliant plan.