if your dogs showing signs of lungworm its probably to late but a dose of ivermec a week apart will sort it , what dog is it ? I give all mine a shot of ivermec every 6 months just to keep on top of things , but lungworm isn't that common in the uk and a lot of other respiratory problems are blamed on lungworm , bayer and your good old vet dick turpin are well versed in bullshitting you out of your money