As many of you are aware, in August of 2004 ProHeart 6, a popular heartworm prevention medication, was voluntarily recalled by its producer — Fort Dodge Animal Health. In spite of the time that has passed, there are still many dog owners that have concerns and misunderstandings resulting from the recall.
ProHeart 6 is the only heartworm preventative available in an injectable form and that lasts for six months. This has made the product very popular with dog owners and veterinarians alike, but recently the FDA Center for Veterinary Medicine became concerned about its use in response to an abnormally high number of "adverse reactions" they had received. In response to this they issued a temporary recall of ProHeart 6, the injectable form of the drug moxidectin.
The FDA has received 5,552 "adverse events" reports for ProHeart 6 through their voluntary self-reporting system. Developed to ease the red tape of reporting problems, this system (available not only to veterinarians, but to the general public as well) has its share of question marks concerning resulting numbers of "adverse events" on both ends of the spectrum. FDA officials contend that many cases still go unreported making the numbers artificially low, while product manufactures point to the high potential for unintentionally false reports being filed, skewing numbers upward and leading to unnecessary concern.
Concerning the ProHeart 6 product, Fort Dodge Animal Health estimates that over 18 million doses have been distributed. This means that even in light of potential reporting errors, given the total number of reports (valid or not) the resulting rate of "adverse events" reported from ProHeart 6 injections was only 3.2 reports per 10,000 doses — or 0.03% incidence rate. While this is of no consolation to those whose dogs may have experienced a problem, these statistics seem to point to the general safety of the drug.
Currently, Fort Dodge Animal Health is complying with the requested FDA recall, and is no longer producing the ProHeart 6 product while an Independent Advisory Panel reviews all submitted "adverse event" reports to determine exactly how many of them represent true incidences resulting from the product. Once this information is obtained, the FDA will make a final ruling on whether the product can be reintroduced to the market.
After reviewing information supplied by the FDA Center for Veterinary Medicine, Fort Dodge Animal Health, and other competitors in the heartworm prevention market, it seems reasonable to take the following precautions, while maintaining an optimistic outlook concerning the safety of ProHeart 6:
Understand that most adverse reactions occur within hours or days of an injection. This means that if your dog received one or more ProHeart 6 injections and is not currently showing signs of illness, there is no evidence that it is at any risk from previous injections.
If you are concerned about your dog's current health status you should have them examined by a veterinarian and allow bloodwork to be performed to assure that all organs are functioning normally.
It is imperative that your dog continues to receive heartworm prevention. There is no reason to not to use heartworm prevention products, indeed the danger from heartworm disease mandates continued appropriate use of some form of protection. There are many heartworm prevention products to choose from that your veterinarian can prescribe for your dog.
Lastly, stay informed. As new information emerges from the ProHeart 6 investigation the product may eventually be deemed safe and again become available, and/or new recommendations may be suggested.
Hopefully the final analysis of ProHeart 6 will prove that it is (and was) a safe product to use, and that it will once again be available to provide protection for our dogs from the very real and very deadly disease of heartworms. Until that time, discontinuing its use, using an alternative form of heartworm prevention, and allowing animal health experts to determine its true safety, is the most responsible action to take.
Dr. Character is not employed or compensated by any animal health company. His comments concerning a particular product are based on his personal experience and knowledge and do not constitute an endorsement of any such product.