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Some drenches contain more than one anthelmintic ‘active ingredient’ (also simply called an ‘active’), that is, the chemical that is responsible for killing worms. These are often referred to as multi-active drenches.
However, the active ingredients within a multi-active product may not target all of the same worms.
Therefore, multi-active drenches can be considered to be:
A combination contains two or more active ingredients that each target the same worms. The chance of a worm being resistant to all active ingredients in the combination is much lower than for each individual active on its own.
Combination example: products that combine levamisole and fenbendazole both target scour worms, barber’s pole worm and other roundworms.
A mixture contains two or more active ingredients, but the actives target different worms. These give the convenience of a single drench when quite different worms are targeted; however, they should be considered ‘single-active’ against each worm.
Mixture example: products containing praziquantel and ivermectin are targeting only tapeworms with the praziquantel and only roundworms (scour, barber’s pole etc.) plus some lesser parasites with the ivermectin.
A product that is both a mixture and a combination contains two or more active ingredients, where some worms are affected by only one active, but other worms are affected by two or more actives.
Combination and mixture example: products containing levamisole and fenbendazole and praziquantel are combinations against roundworms due to the action of the first two active ingredients, but are only a single active (i.e. praziquantel) against tapeworm.
NOTE: Resistance status of drench groups has general information. However drench resistance is common on many farms, therefore one or more of the active ingredients within a combination or mixture that you use could be ineffective on your farm. You should conduct DrenchTests each 2–3 years and DrenchCheck-Day10s in between to know what drench groups and actives are effective on your property.
The Combination-Drench Efficacy calculator estimates the effect of a combination, once you know the drench efficacy of the actives following a DrenchTest on your property.