At the end of July 2004, there was a American Heartworm Society Symposium held. There are some abstracts of speeches found online but one concerned me, which I include here.

QUOTE:

Evaluation of Efficacy of Heartworm Preventative Products at the FDA
Saturday, July 24, 2004
9:00-9:30 AM

V.A. Hampshire, VMD

The Center for Veterinary Medicine, Federal Food and Drug Administration (FDA/CVM) has authority under the United States Code 21, previously under Section 510.300 and currently under Section 514.80 to monitor for adverse experiences of approved animal products. Although veterinarians voluntarily report suspect drug-related events to manufacturers, firms that market FDA-approved animal products must report serious events to the FDA within 15 working days of the veterinarian or pet-owner’s call to them. Serious adverse drug events are defined as adverse events that are fatal, or life-threatening, or require professional intervention, or cause an abortion, or stillbirth, or infertility, or congenital anomaly, or prolonged or permanent disability, or disfigurement.

Thus, under the present regulations, Canine heartworm preventatives are approved for 100% efficacy after testing in laboratory and field conditions. The sign “in-effect heartworm larvae” is a serious adverse drug event because the resulting condition is life-threatening. FDA/CVM makes frequency of lack of effect reports that are deemed possibly, probably, or definitely drug-related available for review under generic product on its website http://www.fda.gov/cvm/index/ade/ade_web_rpts.pdf.

Surveillance of these reports indicates some failures in all product categories but manufacturer reporting was not uniform until the new rule was enacted in July 2003. Most failures are reported in heartworm endemic states and approximately 18% of all reports have credible purchase and testing history. At this time, it is unclear whether these whether these increases, especially in older monthly oral preventatives, are representative of small failures that have always occurred, or whether there is a true increase in emerging resistance or failures in product efficacy. The FDA/CVM requires widespread compliance among practitioners and manufactures in reporting accurate and timely information in order to make sound label recommendations regarding safety and efficacy of each product.

This presentation discusses the methods, personnel and procedures as well as scoring paradigms utilized by FDA/CVM to assess severity of lack of effect heartworm complaints. Results suggest that manufacturers are improving the quality of reports and that over the next several years, FDA/CVM should be able to give more accurate surveillance information regarding efficacy problems across all product categories. It also indicates that as part of that process, practitioners should return to a more conservative testing schedule, particularly in heartworm-laden regions such as the gulf states, lake states, and lower Midwest region. Such practices will permit FDA/CVM to better interpret both incidence and severity of in-effect and possible patterns of emerging resistance.
UNQUOTE

http://www.heartwormsociety.org/symposiuminfo.htm

Numbers taken from FDA Annual/Cummulative Report on October 1, 2004:

QUOTE:

The Clinical Prophylactic (Safety-net) Story: A Review, an Update, and Recommendations
Saturday, July 24, 2004
9:30 – 10:00 AM

John W. McCall, PhD1

Heartworm (D. immitis) drugs are sufficiently safe, effective, and convenient to prevent heartworm disease in virtually all canine and feline pets. Yet, a 2001 survey of over 18,000 veterinary clinics in the USA indicated that over 240,000 dogs and 3,000 cats were infected. This high level of owner compliance failure is alarming. Fortunately, prolonged administration of some of the macrocyclic lactone (ML) preventives kills not only young larvae but older larvae, "immatures," young adults, and/or old adults as well. Efficacy of 95% or more requires dosing for about 9 to 30 months, with older worms being more difficult to kill. Of the various MLs, ivermectin (IVM) has the most potent safety-net and adulticidal activities, while milbemycin oxime (MBO) has the least activity, and the effectiveness of selamectin (SEL) and moxidectin injectable (MOX-SR) lies in between. Worms recovered from dogs receiving prophylactic doses of IVM, beginning during the growth phase of the worm, are small (stunted) and abnormal in motility and appearance. The unique effects of IVM are related to the age of the heartworms at initiation of treatment. The earlier treatment is started, the more stunted and smaller the worms are and the shorter their survival time. The later treatment is started, the longer the worms live, the more likely antigen (Ag) and microfilariae (MF) will be detected, the higher the Ag and MF levels, and the longer the dog will be Ag- and MF-positive. Drug effects do not appear to be enhanced by increasing the dosage and/or administering the drug at shorter intervals, and it appears that continuous monthly treatment is needed to produce the full effects of the drug.

The American Heartworm Society (AHS) recognizes the safety-net and adulticidal properties of some of the MLs, particularly IVM. For example, the AHS 2003 canine guidelines now state, "it is also beneficial to administer a prophylactic dose(s) of ivermectin for one to six months prior to administration of melarsomine, when the presentation does not demand immediate intervention. The reasoning for this approach is to greatly reduce or eliminate circulating microfilariae and migrating larvae, stunt immature D. immitis and reduce female worm mass by destroying the reproductive system. This results in reduced antigenic mass, which in turn reduces the risk of thromboembolism." The guidelines further add that "the long-term continuous administration of ivermectin generally is not a substitute for conventional adulticide treatment. If arsenical therapy is declined, a lengthy course of prophylactic doses of ivermectin will gradually reduce the number of adult heartworms, but in chronic mature infections this may not be as clinically beneficial." Our observation that no heartworm-positive dogs on IVM have died, while two nontreated control dogs have died, strongly suggests that less active dogs are at virtually no risk to severe thromboembolism and death. It is assumed that heartworm-positive working dogs might be more at risk; thus, any heartworm-positive dog on monthly IVM should be examined by a veterinarian at least once every 4 to 6 months. IVM clearly provides potent "safety-net" activity against older larvae, "immatures," and young adults in cases of owner compliance failure, even when the owner and veterinarian are not aware that the animal is infected, and offers much promise as a unique "soft-kill" treatment for young, and possibly older adult heartworms, with reduced risks.

1 Department of Medical Microbiology and Parasitology, College of Veterinary Medicine, The University of Georgia, Athens, GA 30602.
UNQUOTE

http://www.heartwormsociety.org/symposiuminfo.htm

It appears we need to insist on heartworm tests for BOTH adults and babies (microfilariae)

Recommended Heartworm Testing

Possible alternative:

 

"The Pet Whisperer September 2004 Newsletter"

http://www.thepetwhisperer.com/

Dr.Christian Blake (Dr Blake's assistant and 20 month old Grandson) from his recent newsletter

Posted with permission

I have been caring for dogs for over 20 years all over the United States in many heartworm endemic areas. In all those years, I have never had a case of heartworm disease in one of my patients except for two over 20 years ago before I knew better how to help them naturally repel the disease.

I mainly recommend natural-food diets, colostrum, minimal or no immunization and no monthly wormers or heartworm protection. I recommend also that if there are mosquitoes in your area you use my combination of the blend of the following essential oils; Lemon Grass, Lemon and Eucalyptus oils. Two drops of each per ounce of water and spritz the dogs when they go out in bug infested situations. This mixture works equally well on humans and is my bug repellent of choice for my family and myself. You can order these oils off my website www.thepetwhisperer.com under the essential oil section.

http://www.thepetwhisperer.com/