DOES your practice have a
standard operating procedure in
place for handling cases suspected
of ingesting a poison? If not, a
recent webinar organised by The
Webinar Vet is a very good starting
point from which to create a set of
guidelines.
Nick Carmichael, an RCVS Specialist
in Veterinary Clinical Pathology and
director of Carmichael Torrance
Diagnostic Services (CTDS) led an hour-long webinar discussing
the importance of those first steps
when handling poisoning cases and
the potential benefits reaped from
veterinary
toxicology
testing.
Nick
began by
discussing
the extent of
the problem
across
the UK with the Veterinary Poisons
Information Service (VPIS) estimating
around 40,000 poisoning cases per
year, with around 3% of these being
fatal.
The VPIS also reports a list of
poisons most frequently enquired
about by vets in practice, the most
common being theobromine
(chocolate), followed by NSAIDs such
as ibuprofen, then rodenticides such as
difenacoum, followed by the category
into which lilies, grapes and raisins fall.
The VPIS reports permethrin
as being the number one cause of
intoxication in cats. The most common
causes of fatalities across all the species
are, firstly, by “unknown agents”
followed by metaldehyde, permethrin,
ethylene glycol, lilium and difenacoum
respectively.
Handling the poison case
The above-mentioned poisons are
the mainstay of the VPIS inquiries
and consequently are the most
likely that vets will come across in
practice. However, there is obviously
a huge number of other poisonous
compounds which we could encounter
and it is imperative that we train our
staff to get as much information as
possible about the poison at a very
early stage.
Most scenarios will start with a
telephone call to a receptionist or a
nurse and it is important they are fully
trained to manage these phone calls.
The VPIS provides a poisons check list
which guides staff through a number
of questions which need to be asked
in order to obtain as much relevant
information as possible which can then
be passed onto the VPIS.
Detailed information such as
the full name of the product, the
manufacturer, the strength and
composition of the active ingredient as
well as the excipients are all helpful and
could aid the VPIS to give guidance.
It is also essential we tell our staff to
ensure the clients bring with them
any packaging which the poison was
in, or any other relevant material (for
example, part of an unknown plant or
fungus).
The ‘must-haves’
Nick believes there are three main
resources we should all have access to when dealing with poison cases
in practice, the first being the VPIS.
Subscribing to the VPIS is an absolute
necessity as it provides an information
resource that is vital in ensuring these
cases get appropriate care.
The VPIS also receives excellent
feedback from cases which have been
treated and can consequently guide vets
through treatment regimes which have
proven to be helpful. Other toxicology
resources include books such as the
BSAVA Manual for Common Canine and
Feline Poisons and Blackwell’s Small
Animal Toxicology.
The second is the 24-hour ToxBox
service where the VPIS has teamed up
with VetsNow to provide veterinary
practices with round-the-clock access to the drugs necessary for the
appropriate treatment of poisons.
These include European viper venom
antiserum, methocarbamol for the
treatment of metaldehyde toxicity, and
acetylcysteine for paracetamol toxicity.
If specific drugs are necessary to
treat a specific poison, and these drugs
are not available at the practice, the
VPIS will advise how to access the
ToxBox at a local VetsNow clinic.
The third resource cited by Nick
is to ensure that a practice has access
to appropriate toxicology testing.
He advised there may be cases
where the underlying toxin is not
known. Determining the toxin can
be very useful as it helps to provide a
prognosis for the affected animal and
optimises its therapeutic management.
Toxicology testing can also help to
identify the underlying reasons for
cases of sudden death.
Unfortunately, trying to identify the
causal agent can be like looking for a needle in a haystack
and one of the main
problems with trying
to search out these
toxins is the variation
in pharmacokinetics
for each individual
substance.
The speed with
which certain toxins are
cleared from the blood
and urine needs to be
considered. Drugs
such as rodenticides
can be cleared prior
to any clinical signs
developing but can
often be detected in
the liver.
Some substances
may only be found in urine, such as
“drugs of abuse”. Other drugs may
have caused organ damage prior to
clinical signs developing, such as
ethylene glycol.
For these reasons it is always
important to pick up the phone and
seek the advice of an expert to find
out which are the most appropriate
samples to take for toxicology testing
and whether it is possible to test for
a toxin which you may be particularly
concerned about.
There are several test methods
to pick up toxins which include
colorimetric tests which detect poisons
such as paraquat, and ELISA tests
which detect drugs such as ethylene
glycol. Although ELISA tests are
simple to use and give rapid results,
they have questionable sensitivity and
specificity and can be difficult to read.
Extracting toxins
According to Nick, gas
chromatography-mass spectrometry
(GC-MS) is now the mainstay for
detecting specific drugs and toxins,
and in the words of Nick is a good
“haystack sifter”.
GC-MS works by extracting
toxins dissolved in solvent which
are vaporised and separated by gas
chromatography and then identified
by mass spectrometry. This technique
is highly specific and can detect a wide
range of compounds.
Panels are offered by CTDS
according to the presenting clinical
signs (this is available in table form from
http://ctdslab.co.uk/). It also indicates
the huge number of compounds which
can be detected by this method.
A number of sample types can
be used including blood, urine and
stomach contents (faeces are not
appropriate for GC-MS). Nick strongly
advises taking multiple sample types as
early as possible as we know there are certain toxins which will
have been cleared from
the body within a few
hours of ingesting the
poison. These samples
should be labelled,
dated and stored
(freezing these samples
is fine).
A list of differentials
should be considered
for each case and as
stated previously it is
always wise to seek
advice from the lab on
the likelihood of certain
toxins being detected
and from which
samples.
Nick also reminded
us that this type of testing may also help to identify any poisons which
may be involved in cases of sudden
death. Although a full post mortem
is ideal, some owners may feel more
comfortable with performing less
invasive tests such as obtaining urine
samples by cystocentesis, blood by
cardiocentesis and gastric contents via
stomach tube.
Once again, all these samples can be
frozen and kept for a reasonable time,
especially if the owner needs time to
consider all the options.
Reinforcement
Nick reinforced getting samples from
a patient at the earliest possible point,
which could make the difference
between a successful and unsuccessful
outcome.
He cited a case of a three-year-old
lurcher that presented with seizures
and hypersalivation after vomiting
up blue pellets consistent with
molluscicides. These pellets were
assumed to be metaldehyde and the
dog was treated accordingly.
Unfortunately, this dog died, and
after GC-MS was performed on its
stomach contents it transpired that
these blue pellets were actually another
molluscide known as Methiocarb, a carbamate and which requires a
different therapeutic approach.
There is a possibility that armed
with this information, the appropriate
treatment with atropine could have
been administered and this dog could
have stood a better chance of survival.
This was yet another interesting and
informative webinar organised by The
Webinar Vet and we are lucky to have
access to such great resources including
the VPIS, ToxBox and the expertise
provided to us by external laboratories.
By using these services we surely stand
the best chance of ensuring these cases
make a full and speedy recovery.
