When replacing another heartworm preventive in a heartworm disease preventive program, the first dose of HEARTGARD must be given within a month (30 days) after the last dose of the former medication. If the interval between doses exceeds a month (30 days), the efficacy of ivermectin can be reduced.
What happens if I give Heartgard late?
Most of the monthly heartworm medicines have a safety factor of at least 15 days of protection if a dose is missed. This means that if you're just a week or two late, your pet is likely still within that window of protection and would be unlikely to become infected during that time.
How long after expiration can you use Heartgard?
Identification. 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.
What happens if I forget to give my dog heartworm?
A dog who has missed just two monthly doses of preventative or is late for a heartworm injection can become infected with heartworms.
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