TOPICS IN
MEDICATIONS FOR
POULTRY
Patty Dunn, DVM
Animal Diagnostic Lab
Dept, of Vet. Science
As part of the recent meeting of
the American Association of
Avian Pathologists in Pittsburgh,
Pa., July 8-12,1995, a symposium
was held to address -the topic of
drugs and therapeutics for poultry.
Many aspects relating to the use
of therapeutic agents designed to
control infectious diseases in poul
try were covered by leading
authorities in these areas. Of parti
cular interest to many was the use
of antibacterial drugs.
Answers to the following com
mon questions were presented.
• Why are so few poultry drugs
available?
Dr. Martin K. Terry of the Ani
mal Health Instituie spoke about
the need to improve the review and
approval processes for drugs,
which is currently very cumber
some and costly, in order to allow
more drug approvals in less time.
Terry illustrated the poultry indus
try’s experience with the effects of
the recent slowdowns in animal
drug approval processes. He said
that in the last 10-year period, five
new chemicals have been
approved for use in poultry, only
one of which is approved for thera
peutic (treatment) purposes. Dur
ing that same time interval, many
more useful, effective products
have been taken off the market,
most of which had treatment appli
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cations. In most cases, the product
withdrawals were for reasons
other than human or animal health
concerns. The overall effect has
been a major net loss of useful
antimicrobials.
There are no appropriate
approved drugs to treat several
specific poultry diseases. For
example, there are no legal treat
ment drugs for “blackhead” or his
tomoniasis in turkeys at this time.
Additionally, there are few effec
tive treatments for certain respirat
ory conditions in chickens and
turkeys. Important contributors to
the problem of lack of approved
drugs are the time and costs
involved in the current drug
approval process.
Food animal drugs are often
twice as expensive to develop as a
comparable companion animal
drug or human drug. Not only must
safety and efficacy be tested and
proven in the target animal, but
also safety in the human consumer
of the animal product must be
determined. If the high costs of
getting approval for a drug for use
in perceived “minor” species such
as turkeys, ducks, game birds, and
even chickens in some instances
exceeds the expected sales market
return, then incentives for a phar
maceutical company to pursue
development and clearances are
nil.
Dr. R. Greg Stewart, consulting
poultry veterinarian and scientist
in Watkinsville, Ga., gave some
interesting figures pertaining to the
drug developing process. He said
the average cost to a pharmaceuti
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chemical drag for food animals is
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that it takes an average of 11 years.
More than three of these 11 years
are spent in review of the product
by government regulators. Five
million dollars is the average cost
for a supplemental approval for an
existing drug to expand or change
its use in some way.
• What is being done to enhance
current drug availability?
Dr. Martin K. Terry spoke about
the efforts of industry and the Cen
ter for Veterinary Medicine to
work toward a “flexible labeling
initiative.” The new animal drug
product labels would allow veter
inarians more flexibility in the use
of the products. They would be
able to better tailor drug doses,
routes, etc. to particular disease
indications in particular food ani
mal species.
Terry also described the prop
osed “Veterinary Feed Order”
(VFO) drawn up in response to a
proposed rule by the Food and
Drug Administration (FDA)
designed to take all new therapeu
tic drugs away from feed manufac
turers and require that the drugs be
used only by veterinary prescrip
tion. This plan, if allowed to pro
ceed, could cause problems of
increased costs and lower availa
bility for the poultry industry. The
VFO proposes to keep many drugs
from prescription-only status,
while still fostering a level of vet
erinary involvement above that
which often exists with some
“over-the-counter” medications
sold today.
Dr. Peter Poss, a well-known
turkey veterinarian currently affil
iated with the Veterinary Teaching
Hospital in St. Paul, Minn.,
addressed drug use in the turkey
industry. He proposed that the
approval process be streamlined
by having the FDA retain the
approval process for the safety
aspects of drug testing, while let-
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ting the industry carry out the effi
cacy aspects. He says, “FDA
should not be concerned with effi
cacy since a drag sponsor will not
expend the resources to clear a use
less compound and the industry
will know if it works very quickly,
once it is i the market.”
Dr. Tom Holder, an experienced
broiler industry veterinarian based
in Salisbury, Md., echoed that
thought in his presentation on anti
biotic use in broilers. He said that
efficacy testing needs to be practi
cal, and small pen trials may be of
limited value in predicting a drug’s
usefulness under commercial field
conditions. “A drug company is
not going to spend several million
dollars on a drag that will fail after
six months of use. The industry
will determine the efficacy and/or
the feeding program best suited for
a product,” Holder said. He
encouraged the drug companies
and CVM to work together with
the broiler industry to help meet
drug therapy needs in that area.
• Is it safe to mix different drugs
or other additives to treat poultry?
Dr. Jim E. Riviere, a veterinary
pharmacologist at the North Car
olina State University College of
Veterinary Medicine, spoke on
“drug compounding,” which is the
practice of combining two or more
medications. Riviere pointed out
that while there are a few drugs
approved to be mixed or applied
with another drug for a specific
purpose, most combinations have
not been evaluated scientifically
for compatibility. The all too com
mon thinking that “if one drug is
good, two or three should be bet
ter” is flawed and can be, at best,
wasteful, and at worst, dangerous.
One drug may inactivate or make
another drug unavailable for the
body to use or, it may potentiate
the effects of another drag, leading
to toxicity or long residence of
drag in the tissue. Antibacterials
with different mechanisms of
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action should not be combined in
most instances. Many vitamins
and electrolytes, which are widely
used in the drinking water, can
modify water pH, thereby chang
ing the effectiveness of certain
added antibiotics applied in the
water concurrently. Specific inter
actions relevant to poultry are
known to most poultry veterina
rians who can advise on this
subject.
• How can we better target
appropriate antimicrobials to spe
cific bacterial diseases? “Antimi
crobial susceptibility testing has
become an integral part of the ther
apeutic process,” said Dr. W. Dou
glas Wallman. microbiologist at
the Georgia Poultry Laboratory.
He was referring to the process
whereby a bacterial pathogen is
isolated from diseased birds in die
laboratory, and the specific bacter
ia is reacted against several diffe
rent antimicrobial agents (drugs).
This process determines if the bac
teria can live and grow in the pre
sence of the drug, or if it is inhi
bited or killed by the drug within
the environment of the test system.
The test is a good predictor of
whether or not a given drug, if
applied correctly, will work to lim
it the infection in the flock. The
antimicrobial susceptibility test
tends to be a better predictor of
drugs that will not be effective
(bacterial resistance) than those
that will work (bacterial sensitivi
ty), but still serves as the best tool
available for medication selection.
In certain instances, a drug treat
ment may be started immediately
once a tentative diagnosis of a cer
tain bacterial disease has been
made (0-24 hours after the birds
have examined). Meanwhile,
an antimicrobial susceptibility test
will be set up, with results often
available by 48 hours. At that time,
if the drug being used is deter
mined to be ineffective, a switch to
(Turn to Pag* E 10)
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