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 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.
What happens if you miss 2 months of heartworm medicine?
I have missed 2 months of heartworm prevention for my dog. What should I do? You need to consult your veterinarian, and immediately re-start your dog on monthly preventive—then retest your dog 6 months later.
How long can my dog go without heartworm medicine?
Any time a dog goes more than six weeks without heartworm prevention the dog is at risk of infection. Dogs with mature infections (in which hearworms are mating and producing larvae in the bloodstream) may experience a shock-like adverse reaction to heartworm prevention.
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