Ivermectin showed up in a variety of forms:
¨ 1] a once a month heartworm preventative
¨ 2] a solution taken orally or by subcutaneous injection to eliminate intestinal worms, scabies and ear mites.
¨ 3] an adjunct therapy for treatment of demodectic mange
¨ 4] a topical ear drops specific for ear mites
¨ 5] a microfilaricide oral solution

The problem in collies and some other breeds was that sometimes the ivermectin not only killed the parasites, it also killed the dog!!!

For years, the pharmaceutical companies tried to convince the collie owners and breeders that ivermectin was a safe drug for collies. They even put a picture of a sable collie on one of their ivermectin products.

Some of our collies did well and had no adverse reaction to ivermectin administration. A lot of our collies became ill, some even died. Death was usually a result of the increased levels of ivermectin in the brain.

Here are two of my own ivermectin sensitive nightmares…………

When we sell a puppy, it goes to its new owner with a warning label. The puppy also takes a note directly to the new veterinarian on its first visit to the veterinarian’s office. The warning label and the note explain some of the sensitivities of collies to certain drugs. Ivermectin is top of that list. The note says DO NOT USE IVERMECTIN UNDER ANY CIRCUMSTANCES.

Puppy number 1 received one labelled dose of heartworm preventative containing ivermectin. The puppy spiked a fever, started to convulse and died within 24 hours.
Puppy number 2 had some hair loss on its foot. The area was scraped and was negative for demodectic mange. Still thinking it might be demodex, 1cc of liquid ivermectin was applied to the foot. That night the puppy became ill, started to convulse, and died.

Now Dr. Mealey has determined the mechanism and consequently the gene responsible for adverse reactions to ivermectin in collies. P-glycoprotein [P-gp] is the neurotransmitter [vehicle] responsible for keeping ivermectin out of the brain. Dr. Mealey has found that if the protein [P-gp] is present then ivermectin cannot enter the brain, hence no reaction. The absence of P-gp allows ivermectin to cross into the brain and allow adverse reactions.

Dr. Mealey has also determined the heritability of ivermectin sensitivity. There are three populations of these dogs. One is homozygous for the production of P-gp. These dogs are not sensitive. The second population is heterozygous for the production of P-gp. These dogs are not sensitive to ivermectin but can produce puppies that are sensitive when bred to another heterozygote or an ivermectin sensitive dog, and third, the homozygous ivermectin sensitive affected dogs that do not produce P-gp.

Dr. Mealey has determined ivermectin sensitivity to be widespread in the collie population. Thirty five percent are affected and show sensitivity, whereas 42% are carriers. That leaves 23% to be ivermectin non-sensitive non-carriers.

A test is in development to screen for the presence or absence of the gene responsible for the production of P-gp. Testing individual collies will allow us to predict the sensitivity of that particular collie to ivermectin.

Now it seems that all we should have to do to eliminate the ivermectin problem is avoid ivermectin. TRUE!! But, go one step further. P-gp is responsible for keeping other drugs out of the brain. Those collies that have lymphona or leukaemia, or those that have autoimmune blood disorders would benefit by the use of vinblastin and/or cyclosporine. In the absence of P-gp, the drugs cross the blood brain barrier and can cause death. Loperamide [immodium], an anti-diarrhoea drug will also cross the blood brain barrier in the absence of P-gp. Death by immodium has been anecdotally reported in collies. Now we know why.

This is only the beginning of the list of drugs that are affected by P-gp. Soon we will be able to test our collies for the ability to handle P-gp affected drugs before using them. We will no longer have to find out if reactions occur after administration of often necessary, but potentially dangerous drugs. Often these reactions result in death.

If you would like to learn more about this incredible discovery, visit Dr. Mealey’s web site at:
Http://www.vetmed.wsu.edu/announcements/ivermectin/ownerinfo.html

[Reprinted with the kind permission of Dr Mealey]