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.
Can I give my dog heartworm medicine late?
A: Give the dose you missed immediately, then continue giving the medication on the day you've always given it. If the missed dose is more than 2 weeks late, your dog should be tested for heartworm again in six months (click here to learn why).
How late can you give Heartgard?
The final dose must be given within a month (30 days) after the dog's last exposure to mosquitoes. 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.
What happens if I forget to give my dog his heartworm pill?
A dog who has missed just two monthly doses of preventative or is late for a heartworm injection can become infected with heartworms.
Is it OK to give heartworm a week late?
Less than 2 weeks: Give your dog the missed dose immediately. Your dog will be protected from heartworm disease because you will still be within the 45-day grace period in which the preventative is effective.
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