I agree with Scratchin' Dog.Originally Posted by hogdog
Wormers like pyrantel and fenbendazole are the preferred choices for pups, precisely because they kill worms with zero toxic effect on pups (even at 20x the recommended dosage).
Wormers like ivermectin, and especially the related and more toxic moxidectin, are both fantastic wormers ... but if you understood HOW THEY WORK ... by killing worms' central brain system (while not being able to do so against higher mammals due to the blood-brain barrier that mammals have) ... and if you further understood that very young pups do not have a fully-formed blood-brain barrier yet ... you would realize WHY all label indications recommend against using these drugs on pups younger than 4 months. Their brains and resistances to certain drugs are not fully-developed yet.
In fact, this same reason is why some herding dog breeds (e.g., collies) are susceptible, precisely because they have a mutation to their MDR1 gene which allows higher levels of these drugs to cross the blood-brain barrier into the animal’s central nervous system. This is why one must be cautious while using ivermectins on collies too, because it can kill them.
Anyway, I went into detail like this, because it is helpful to actually know WHY certain practices are to be taken (or avoided). Some people get away with giving ivermectin to pups younger than 4 months, but I know plenty of folks who have killed their whole litters by doing so, especially using moxidectin.
And that will never happen using either pyrantel or panacur. However, keeping in mind that it takes about 4 months for heartworm microfilaria to migrate from the blood to the heart, you also don't want to wait any longer than 4 months to give ivermectin (or equivalent) to your pups either.
So 4 months is the magic number
Cheers,
Jack
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