i am just seeing this but i would seriously question your vet on his decision to do the OLD arsenic treatment method of treating HWs. There was a new drug introduced that is much easier on dogs and does a much better job of killing heartworms in dogs. Its a seriesof injections in the dogs back muscle that work much better and with fewer side effects than the arsenic treatment. This widely available drug is called immiticide.
Melarsomine (immiticide) is preferred over another drug, thiacetarsamide, that kills adult heartworms because it is less likely to cause a reaction where injected, it is more effective, less likely to cause liver damage, and can be used more safely in dogs with severe heartworm disease.
thiacetarsamide goes in the vein and is horrible horrible crap. both contain types of arsenic but Immiticide is much easier on the dogs liver than Thiaceta. You will have to confine Brody for a period on each drug but Immiticide is much much safer.
please ask your vet which drug he uses. even contemplate I wish you luck in your journey--