Preventing heartworm infection is as easy as obtaining heartworm medicine from your veterinarian. To learn more about preventive heartworm medication, including different types of drugs and their effectiveness, keep reading.

Brands of Heartworm Medications

In the U.S., the drugs approved for heartworm prevention are moxidectin (sold under the brand ProHeart), ivermectin (a popular drug usually sold as Heartgard) and milbemycin (also known as Sentinel or Interceptor). These drugs are usually sold as pills and are available at most veterinarian offices.

Moxidectin is also available as an injection that covers either a 6-month or 12-month period and is administered by a veterinarian, but not in the United States. Pet owners in Japan, Canada, Australia and Korea can obtain moxidectin injections under the brand names ProHeart6 and ProHeart12.

Feline owners can turn to products like selamectin, a topical cream which is typically known as Revolution for Feline; ivermectin, also known as Heartgard, but for cats; and milbemycin, also known as Interceptor.

How Effective is Heartworm Medicine?

Preventive heartworm drugs are very effective and when regularly administered will protect more than 99% of cats and dogs from heartworm infection.

Usually, if a heartworm medication fails, it is because of pet owner error - the person did not administer the heartworm pills on schedule or did so incorrectly. That said, the monthly doses are fairly effective, so if a month is missed, most animals are still protected as long as the next two month's doses are administered on time.

How to Administer Heartworm Drugs

You should start your heartworm drug regimen at least a month before mosquito season begins. Then, the monthly treatment should continue through mosquito season and for a month afterward. Of course, ask your veterinarian for guidance and medical advice.

In tropical and sub-tropical climates with year-round mosquito activity, most veterinarians recommend that animals take heartworm prevention drugs throughout the entire year. Some also recommend it for colder regions, but it's not typically necessary unless you plan to travel with your pet.

Most heartworm drugs are available as chewable tablets. For pets that don't like taking pills, veterinarians often recommend hiding the pills in their food.

Side Effects of Heartworm Drugs

Side effects for most heartworm drugs are rare, but this may be because it is difficult to diagnose unapparent side effects or impacts that aren't obvious. Remember, your dog can't tell you that he's having a headache.

However, higher doses of heartworm medicine can cause diarrhea, tremors, weight loss, vomiting and possibly death. It's important to never give your pet a double dose and to keep your heartworm medication safely out of reach of both your pet and your children.