Well, actually ask your vet about Ivermectin
I grew up on a pig farm but that was before Ivermectin was made - any lice we just squashed. Now I don't have any pigs - still love them though!
My concerns with Ivermectin are to do with it passing through animals and continuing to kill worms, but this time in the soil. It is very persistant and will have a detrimental effect on the pasture, because earthworms help to aerate the ground and to draw litter etc down into the earth to be recycled, so a reduction in numbers is not good. When manure is composted or stacked in a muck heap, if the animals have been wormed with Ivermectin, the heap will not rot down for a long time.
I don't know if this effect would also happen with an injected dose.
You need to buy it from your vet anyway, so you can ask him what he recommends