Use of Baycox liquid or Marquis paste to control coccidiosis in

by Lorraine Shelton and Della Hengel

Baycox (toltrazuril) is a new treatment that may actually cure
coccidiosis, instead of just suppressing it. The drug is available
in Canada, but not the US. Albon and Tribrissen are used for years
to control coccidia infection, but they don’t cure it and the animal
may continue to shed spores. Marquis paste is made from a similar
drug, ponazuril, which is a metabolite of toltrazuril.

Baycox may be obtained from Interpet: or from Pet Supplies International:
Since the Baycox is a special order item, it’s not shown on
the PSI website. You need to email the owner (who incidentally is a vet): (Geoff Turnbull). No prescription is needed. If
you’re in the US, the cost for 200 ml (the only size it comes in, original
Bayer packaging — he does NOT repackage) at today’s exchange rate is
under $90. DO NOT use the 2.5% solution sold as a pigeon remedy, as it can be caustic to the mucus membranes of cats.

Do not use this drug in pregnant cats as the terratogenic effects of
this drug has not been adequately researched as yet.

The dose of Baycox is 20 mg/kg (10 mg per pound). This is 0.2 ml per pound
of cat when using the 5% suspension. In a published study, a single
dose of Baycox cured coccidiosis in puppies, as long as adequate
environmental clean-up is performed. However, I’d recommend repeating
it weekly for a couple of weeks. Clean up of the environment is
critical to get rid of coccidia. This drug works best when it is used
at the age of 4-6 weeks to PREVENT coccidia infection in kittens.

An alternative to Baycox is the similar drug ponazuril, marketed as
Marquis paste for horses. The dose is 20mg/kg once a day for 1-3 days.
The paste contains 150mg ponazuril per gram of paste. The plunger is
marked for horses weighing 600 – 1200 pounds. You want to take the
amount for a 600# horse and dilute it to a total volume of 14 ml in
something tasty. Dose at 0.1 ml per pound of cat. Discard the unused

Here is the journal abstract I posted to the list in 2001:
Toltrazuril treatment of cystoisosporosis in dogs under experimental
and field conditions. A Daugschies, HC Mundt, V Letkova
Parasitology Research, 2000, Vol 86, Iss 10, pp 797-799

Coccidia of the genus Cystoisospora cause mild to severe diarrhoea in
dogs. The effects of toltrazuril treatment on cystoisosporosis were
studied under experimental and field conditions. Twenty-four puppies
were experimentally infected each with 4 x 10(4) oocysts of the
Cystoisospora ohioensis group. Three groups of six puppies were
treated 3 dpi with 10, 20 or 30 mg/kg body weight of toltrazuril
suspension (5%); the remaining six puppies served as non-treated
controls. Toltrazuril suspension or microgranulate were given once
in a dose of 10 or 20 mg/kg body weight, respectively, to naturally
infected puppies in conventional dog breeding facilities, depending
on the coproscopical evidence of infection. Oocyst excretion and
clinical data were recorded.

Under experimental conditions, the non-treated puppies excreted
oocysts beginning at 6 dpi and suffered from catarrhalic to
haemorrhagic diarrhoea. On 12 dpi, four of six non-treated puppies
died. Irrespective of the dose, toltrazuril treatment totally
suppressed oocyst excretion and no diarrhoea or other signs of
disease were observed in the treated groups. Natural Cystoisospora
infections were regularly found during the 3rd or 4th week of age
in dog breeding facilities although not always associated with
diarrhoea. A single oral application of toltrazuril abrogated oocyst
shedding and the treated puppies remained generally coproscopically
negative during the following 2-4 weeks.

Cystoisospora is pathogenic for puppies and can induce severe
disease. Natural infections are common in conventional dog breeding
facilities. Toltrazuril treatment is suitable for controlling
cystoisosporosis under experimental and field conditions. A single
oral treatment for puppies in the 3rd/4th week of age is recommended.

Here is some information directly from Dr. Bruce Kilmer at Bayer

Thank you for your interest in Baycox. Unfortunately, Baycox
isn’t registered for cats and therefore I can’t provide a package
insert. On a second point, Baycox is not available in the US, except
black market goods coming in by whomever. Bayer In Canada can not
sell product into the US. Baycox is a triazine derivative. The drug
active is toltrazuril, which has a cidal mode of action on protozoan.
The toltrazuril will kill all single cell stages of coccidiosis. Once
an animal has diarrhea and you can find oocysts on fecals, the drug
can not penetrate the oocysts so technically it is too late to treat.
In the actual clinical cases, treatment is still worthwhile to shorten
the length and severity of the diarrhea as there is still development
of the life cycle in the small intestine that will be controlled.

The idea is to dose the cat before there are clinical signs. For
example, the normal situation would be a cattery having regular
problems with coccidiosis in young kittens. The kittens normally would
break with diarrhea at about 5 weeks of age. The treatment would be
given around day 28, killing the early stages of the protozoa and
preventing clinical disease. You will not have the history on a
rescue cat so treatment would be best at the earliest hint of an
outbreak and then repeat treatment in 7 days.

Baycox treatment will not cause sloughing of the intestinal
epithelial cells. The coccidiosis does a fine job of that on its own.
We have electron micrograph studies of sections of intestine 24 hours
post treatment with Baycox. The intestinal cells remain intact and
functional while the single cell stages of the cocci are dead, as
evidenced by staining techniques. because Baycox is cidal, the kitten
does not have to depend on its immune system to eliminate the cocci as
what would occur with a static drug like sulfadimethoxine.

Remember that Baycox should be given during the preclinical stage.
This is very difficult to judge as the kitten will be at a stage when
it is infected but the cocci are only in the first stages of their life
cycle. The intent is to kill the protozoa before there is damage to the
villi to clear the infection. In this way, the kittens will not develop
the normal clinical signs of diarrhea. If you can identify oocysts on
fecal exam, the damage has already been done and the protozoa has
completed its reproductive cycle. Drug can not penetrate the oocyst wall
to kill this stage. Treatment at the first signs of a clinical case will
still help to limit the severity and duration of the infection as the
Baycox will kill the single cell stages that have not reproduced
sexually yet.

Try to determine the usual age that you see outbreaks. For example, many
catteries will see diarrhea sometime around day 35. The time to treat is
therefore at day 28. Likely the kittens had an infective dose of oocysts
by this stage but minimal damage has occurred. Treatment will eliminate
the coccidiosis before there is damage and the kittens will not break
with diarrhea. Studies in other species indicate that the animal will
have developed immunity to subsequent exposure.

The dose is 20 mg/kg by oral dosing.

Toltrazuril is quite lipid soluble so absorption and distribution into
tissue is very good. Baycox has a unique mode of action and there is no
reason to be concerned with an adverse reaction or a drug-drug reaction.
We have never had an adverse reaction reported after millions of
treatments, often concurrent with other medications.

I have never heard of any adverse reactions to treatment at this dose
in puppies or kittens or on the repeat seven days later. As Baycox only
has activity against protozoa, there is no effect on upset of intestinal
flora and the formulation is very well tolerated. The only time I have
heard of any reaction occurred when someone used the Baycox 2.5% Poultry
Concentrate by direct oral dosing in 3 day old piglets. This formulation
is designed to be diluted in the drinking water for poultry. To be
soluble in water, the product undiluted is very alkaline, pH 11.4.
Direct oral dosing of the undiluted product is very irritating to
mucous membranes and will cause immediate vomiting. Make sure you are
using the correct formulation.

Bruce Kilmer DVM
Manager, Veterinary Affairs/Product Development Bayer Inc.