re: Update in OP; Treating young lab for heart worms

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Recent information has come to light that Heartgard may be only 95% effective, rather than 100% effective, in preventing heartworm infections. That means it will destroy 95% of heartworm larvae, not that 95% of dogs receiving Heartgard will remain heartworm-free.

The dosage of ivermectin used in Heartgard was the lowest found to be 100% effective at killing heartworm larvae when the product was originally approved. Since lower doses were less effective, it's possible that higher doses may continue to be 100% effective.

Higher doses of ivermectin are safe for all dogs except those with the MDR1 mutation. Dosages as high as 50 times the amount used to prevent heartworms are used to treat mites on dogs (demodectic mange). Very high dosages may also be problematic for dogs infected with Heartworms, and those being treated with Comfortis. See Ivermectin Sensitivity above for more information.

It may be best to double the amount of ivermectin you give your dogs in order to potentially provide better protection from heartworm infection. Again, this does not apply to dogs with the MDR1 mutation.

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