Sentinel Spectrum for large dogs 22-45kg (50-100lbs). Each pack contains 6 tasty chews, one to be given monthly. For the prevention of heartworm, the long term control of fleas and the control of all intestinal worms including tapeworm. This is Australian registered product labelled in kilograms. Dog heartworm prevention, Sentinel for dogs.This product should only be administered if your dog has been on a regular heartworm preventative program. Consult your veterinarian if you have not used a heartworm preventative on your dog before, or if there has been a period where treatment has lapsed.