Questions and Answers
January, 1996
Dear Dr. Silverio,
My question is related to the use of Ivermectin. Is it safe to
use as a heart wormer? Is it really effective on other worms,
whip, round and hook?
What would the proper dosage be? All beaglers I talk to use this
drug. My vet does not recommend it because it is not approved for
hounds. The interceptive I use seems to work, but gets expensive
for my 9 dogs. I would like to save money if it is a safe and
effective change.
Please give me your opinion, with correct dosages, because I've
heard from 1/4 cc to afull cc as the correct dosage.
Thank you for your time,
David Leonello, NY
Dear David,
Ivermectin is a broad spectrum antiparasitic agent that has been
licensed in the U.S. since 1983. It acts by interfering with
nerve function to cause paralysis and death in many internal and
external parasites of livestock and pets. It is available in
injectable forms for cattle and swine, as an oral liquid for
sheep and as a paste, or liquid, for horses.
The only form approved for use in dogs is as heartworm
preventative pills (Heartgard - 30, from Merck) which contains a
very low level of the drug. The dosage used to prevent heartworm
disease is only 3 - 6 micrograms per pound of body weight, given
orally once a month. Only about 1% of dogs receiving Heartgard
will show mild side effects. A much higher dose of Ivermectin (50
mcg/lb) is required to kill adult hookworms and whipworms, and an
even higher (100 mcg/lb) is about 90% effective against the
common roundworm of dogs, Toxacara canis. These higher doses may
never be approved for use in dogs because some rare
individuals, usually Collies, are actually sensitive to the drug.
In those dogs, these higher doses can cause excitability or
depression, coma and death. Most dogs require 5000 mcg/lb to
cause neurologic side effects.
The safest and the only FDA - approved medications to control
intestinal worms and prevent heartworm infection are
Heartgard-Plus, which also contains pyrantel to kill hooks and
rounds, and a totally different drug, millemycin (Interceptor,
from CIBA), which controls hooks, rounds and whipworms. Both of
these prepackaged medications can be expensive for those who have
a large number of dogs. A much less expensive alternative
involves extra-label use of the injectable bovine product (Ivomec
from Merck). To achieve the dose of 100 mcg/lb, Ivomec should be
given orally at 0.1 cc for every 10 pounds of body weight. This
is equivalent to 1/4 cc for a 25 pound beagle and can be given
once a month to prevent
the diseases caused by the four parasites mentioned. All dogs
should be tested for heartworm disease before the first dose.
In our clinic, we have used Ivomec at that dose to treat
Sarcoptic mange in dogs and ear mites in cats, with no side
effects observed or reported. However, widespread regular use in
hundreds or thousands of dogs would increase the chances of
finding one sensitive individual. Therefore, anyone using the
drug in this manner must understand that it is extra-label usage,
not approved by the FDA.