What Happens if a Dog Is Late Taking Heartworm Pills?

Heartworms are transmitted through the bite of an infected mosquito.
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Heartworm pills prevent larval heartworms from maturing into adults and infesting a dog's lungs and heart, where they can cause serious disease and, occasionally, lifelong damage. Heartworm pills must be given at the same time every month to effectively disrupt the heartworm life cycle. If your dog took his pill late, or you suspect that your dog missed a dose, the veterinarian can answer questions and prescribe treatment.

Missing a Dose

Heartworm medicine eradicates larval heartworms younger than 6 weeks old. Once reaching adulthood at 45 days, the heartworms begin their 6-month migration to the lungs and heart, where they may grow to a foot long and cause irreparable damage. Heartworm preventatives do not kill adult heartworms. Experts at the Priority Pet Hospital recommend giving the dog his missed dose immediately, and continuing to give him his medicine on the scheduled date in subsequent months. If the pill is more than two weeks late, the dog will need to return to the veterinarian for a heartworm test six months from the date of the missed dose.

Testing Blood

If a dog misses his heartworm pill by more than a few weeks, his blood should be tested by a licensed veterinary professional to check for the presence of adult heartworms, according to Priority Pet Hospital. This test is performed after a period of six to seven months, so that any heartworms present in the dog's body will have reached adulthood. The blood test will scan for proteins produced by female heartworms and, if found, is proof positive of an infestation. The dog will then need to undergo a more rigorous treatment regimen to kill the adult heartworms.

Annual Exams

Most veterinarians recommend a routine yearly test to check for the presence of heartworms, according to Purdue University. Dogs can throw their pills up or spit them out, losing their monthly protection in the process. Products may fail from time to time. If a dog becomes infected with heartworms, administering his preventative pill can hurt him. Once the veterinarian has determined that the dog is healthy, he can renew the dog's prescription for his monthly pills.

Keeping a Schedule

Most veterinarians recommend year-round heartworm preventative medicine for dogs in all parts of the continent, according to PetMD. Adaptable mosquito species are able to thrive in cool climates, and certain types have been known to overwinter indoors. Not only does regular administration of the pill keep pets healthy in all weather, it keeps dog owners in the habit of giving the pill regularly. Some veterinary practices offer online email reminders that alert pet owners when their dog's pill should be given.