ShinBit is receiving a Melarsomine injection to kill the adult heartworms. So Melarsomine is an adulticide and is the Immiticide referred to in the heartworm treatment report.
Remember the adult worms can live in the heart and pulmonary arteries which is why heartworms get their name. Melarsomine is the only medication currently being used to kill adult heartworms. Because it is injected into the muscles of the back, the injections can be painful.
Doxycycline is also used to kill the Wolbachia organism infection that often accompanies heartworm disease. This organism is thought to also provide some sort of protection for adult heartworms and may cause inflammation in the lungs of the infected animal after the adult heartworms die.
The dying heartworms can cause obstructions in the blood vessels of the lungs. Exercise can increase the risk of an embolism and serious side effects so ShinBi must be kept quiet and inactive during his heartworm treatment.