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.
What happens if I miss a month of heartworm medicine for my dog?
If it has been less than two weeks since the missed dose, give your dog the dose immediately. If it has been over two weeks since the missed dose, contact your vet, who will likely advise you to resume normal dosing next month and have the dog tested for heartworm in six months.
What if I forget to give my dog his heartworm medicine?
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 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.
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.
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