How Long Does Heartworm Medication Really Last. According to the pet center, the expiration date on all dog medications is the date after which the product can no longer be legally sold, but heartworm medication can still be used in the first few months after that date. Heartworm preventatives don’t touch them, not matter how many you give.

Medication still in powder form is probably still good for 1 to 2 years beyond the expiration on the label. The heartworm industry authority, the american heartworm society (and their cat heartworm site ) offers a wealth of information. Despite the fact the heartworm pill is given monthly to dogs, the heartworm drug stays in a dog's system for about 24 hours, explains veterinarian dr.
