Brand: DECTOMAX ® Pour-on for Cattle

Company: ZOETIS

FORMULATION: «pour-on» for topical administration. To be applied along the topline in a narrow strip extending from the withers to the tailhead.

ACTIVE INGREDIENT(S): doramectin 5 mg/mL (=0.5%)

CHEMICAL CLASS of the active ingredient(s): macrocyclic lactone


PARASITES CONTROLLED* (spectrum of activity)

* Country-specific differences may apply: read the product label.


  • Cattle: 500 mcg/kg bw (= 227 mcg/lb), equivalent to 1 ml/10 kg (=22 lb) bw

* Can be slightly different in some countries: read the product label!


  • LD50 (acute oral) in rats: 1000-2000 mg/kg (a.i. according to MSDS)
  • LD50 (acute dermal) in rats: 500-1000 mg/kg (a.i. according to MSDS)
  • Estimated hazard class according to the WHO: not applicable for veterinary medicines

Suspected poisoning? Read the article on doramectin safety in this site.

Withholding periods (=withdrawal times) in days for meat & milk (country-specific differences may apply: read the product label)

  • Meat: USA 45 (do not use in calves to be processed for veal); Canada 55 (do not use in calves to be processed for veal); UK 35; Australia 42.
  • Milk for human consumption:
    • USA: Not approved (Not for use in female dairy cattle 20 months of age or older);
    • Canada: Not approved (non-lactating dairy cows must not be treated within two months of calving);
    • UK: Not approved (do not use in dry cows or pregnant dairy heifers within 60 days prior to calving);
    • Australia: NIL.

The different withholding periods in various countries illustrate the fact that unfortunately, national regulatory authorities often draw different conclusions from the same scientific evidence. This has been always so and there are no indications that things will improve in the near future. Whereas this product is not approved for use on dairy cows in most countries, it is approved in Australia with a NIL withholding period for milk. This is probably related to the approved doramectin MRL in bovine milk (= 15 ppb = 15 mcg/kg) by some registration bodies, which has not been adopted everywhere. Where such a doramectin MRL for bovine milk is not set at all, any doramectin residues in milk are illegal. In the absence of an MRL most manufacturers don't even test the behavior of their doramectin formulations in dairy cows, i.e. they had no data on milk residues at all. The only possible use recommendation was not to use the product on dairy cows. Where an MRL is set, manufacturers can generate data and present them to the registration authorities in order to get the approval of a withholding period for milk. Some manufacturers may present such data for their doramectin products, some may not, or not for all their doramectin products, for whatever technical or marketing reasons.

WARNING !!!: Never use on humans, dogs or cats.

You may be interested in the following articles in this site dealing with the general safety of veterinary products:


Risk of resistance? YES, reported in gastrointestinal roundworms in cattle in several countries particularly in the following worm species: Cooperia spp and Ostertagia spp.

Resistance of gastrointestinal roundworms to macrocyclic lactones in sheep, goats and cattle has been reported in numerous countries. Most cases have been reported for ivermectin, but doramectin shows cross-resistance with ivermectin. Based on the very abundant and frequent use of ivermectin and other macrocyclic lactones in livestock (with more-or-less cross-resistance to ivermectin) it must be assumed that resistance of gastrointestinal roundworms to this chemical class will continue spreading and strengthening in the future.

This means that if this product does not achieve the expected efficacy against the mentioned parasites, it may be due to resistance and not to incorrect use, which is usually the most frequent cause of product failure.

Alternative chemical classes/active ingredients to prevent resistance of gastrointestinal roundworms through product rotation:

These alternative products may not be available in all countries, or may not be available as pour-ons.

Resistance of cattle ticks Rhipicephalus (Boophilus) microplus to ivermectin, another macrocyclic lactone, has been reported in several Latin American countries. It is not yet a widespread problem, but nevertheless a warning. Based on the intensive use of macrocyclic lactones on cattle it is only a matter of time for resistance of cattle ticks to these compounds to develop elsewhere unless specific resistance preventative measures (e.g. rotation, IPM, etc.) are taken.

Learn more about resistance and how it develops.


Are the active ingredients of this product ORIGINAL* or GENERICS**?


*Meaning that they are still patent protected and generics are not yet available
**Meaning that they have lost patent protection and may be acquired from manufacturers of generic active ingredients other than the holder of the original patent.

COUNTRIES where this brand/product is marketed: Worldwide, including the US, Canada, the EU, Australia, etc. In some countries marketed by other companies.
GENERIC BRANDS available? YES, but rather few, if at all, in most English speaking countries. It happens that many Animal Health companies without an own macrocyclic lactone (ML) for livestock prefer generic ivermectin instead of doramectin or other MLs. A simple reason is that ivermectin was the first ML that lost patent protection and became available in the generics market. Another one is that the offer of generic ivermectin is much higher and thus prices lower than for doramectin or other MLs (e.g. moxidectin, eprinomectin, etc.). Although doramectin may have some advantages over ivermectin in particular markets, ivermectin is often good enough for most indications.

Click here to learn more about GENERIC vs. ORIGINAL drugs.

For an overview on the most used antiparasitic pour-on brands click here.


DECTOMAX Pour-on for cattle was the topical formulation of doramectin that followed the 1% injectable launched by PFIZER (now ZOETIS) in the mid 1990s. After the tremendous success of ivermectin in the 1980s, all multinational Animal Health companies concentrated their efforts on discovering their own macrocyclic lactone comparable to ivermectin. PFIZER was one of the few companies that made it and introduced even two own macrocyclic lactones: doramectin for livestock and selamectin for dogs and cats.

Doramectin is a broad spectrum macrocyclic lactone introduced in the 1990s for use in livestock. It is neither used in pets nor in agriculture. It's spectrum of activity is similar to that of ivermectin. It is generally considered as more potent than ivermectin against gastrointestinal nematodes of livestock, particularly in sheep and goats, and against a few other livestock pests (e.g. sheep scab, cattle ticks, etc.). It is also less toxic than ivermectin, which allows higher safety margins.

Besides convenience aspects, the doramectin pour-on formulation has the advantage over the injectables that it also controls horn & buffalo flies and biting lice,  (in Australia and Latin Amefica also cattle ticks) which are not controlled by the injectables.

But it has also disadvantages. In several scientific studies it has been shown that ivermectin administered as a pour-on is not "automatically" absorbed through the skin. Licking (self licking or licking of other treated animals) may account for >50% of the total intake, compared with only about 10% absorbed directly through the skin. This is the reason why a dose of 500 mcg/kg bw is needed after pour-on treatment, compared with only 200 mcg/kg bw after injection. And it has been also shown that intake of topically administered active ingredient in some cattle may be twice as high as in other ones, all treated at the same rate. The reason is that individual cattle show a different licking behavior. An important practical consequence is that the quantity that is finally ingested and is therefore available for the control of gastrointestinal worms depends on the licking behavior of the treated animals. "High lickers" can be overdosed, whereas "low lickers" can be underdosed. And chronic underdosing of animals in a herd may enhance development of resistance to ivermectin and other macrocyclic lactone in gastrointestinal roundworms.

To our knowledge similar studies have not been carried out with the DECTOMAX Pour-on, but it must be assumed that the licking-behavior of cattle affects intake of doramectin in a comparable way. A similar effect of the licking behavior on the intake of active ingredient after pour-on administration has also been shown for fluazuron, a tick development inhibitor.

Absorption through the skin is also negatively affected by the thickness of the skin and the hair coat, by dust and mud on the coat, by product lost on fences and yards, etc, factors that don't play a role after injection.

In contrast with the injectables, the pour-on formulation should not be administered to wet animals, and rain shortly before (up to 6 hours) or after administration can cause product run-off and thus under-dosing. The pour-on shouldn't be administered by strong winds that may blow away part of the product and/or contaminate the workers.

For these reasons efficacy after pour-on administration is usually less reliable than after injection.

There are other doramectin formulations for injectable administration, mainly for cattle and sheep.

Being an excellent antiparasitic, comparable to ivermectindoramectin does not control all parasites of livestock. Unfortunately advertising and even the label of some generic formulations in less developed countries often include unsubstantiated claims. To help preventing confusion and misuse it is useful to know that whatever doramectin pour-on (without additional active ingredients) used at the recommended dose of 500 mcg/kg DOES NOT CONTROL:

Click here for general information on good practices for the prevention and control of gastrointestinal worms in livestock.


This article IS NOT A PRODUCT LABEL. It offers complementary information that may be useful to veterinary professionals and users that are not familiar with veterinary antiparasitics. 

Information offered in this article has been extracted from publications issued by manufacturers, government agencies (e.g. EMEA, FDA, USDA, etc.) or in the scientific literature. No guarantee is given on its accuracy, integrity, sufficiency, actuality and opportunity, and any liability is denied. Read the site's DISCLAIMER.

In case of doubt contact the manufacturer or a veterinary professional.