Re: Withdrawal Rates (fwd)

[Trish Dowling <dowling@skyway.usask.ca>]

> 
> Date: Sun, 26 Jul 1998 14:28:54 -0700
> From: krisolko@juno.com (Kristen L Olko)
> To: ridecamp@endurance.net
> Subject: Withdrawal rates
> Message-ID: <19980726.142856.3662.0.krisolko@juno.com>
> 
> What's the withdrawal rate for azium?I have a horse with scratches who's
> being treated with it and a ride in 1 week. I want to know when to take
> her
> off it. 

Kristen,
The bottom line is that we are a no drug sport, so if they detect any level of a drug, it's a violation. The 
recommended withdrawal times are based on data from a limited number of horses, so that some horses will fall 
outside the average when it comes to withdrawal times. So it always pays to be conservative about any drug 
withdrawal, and remember that even if you followed a published withdrawal time, if your horse tests positive, you 
are held responsible. Compounding the problem is that there are many different methods of drug analysis, so the 
level of dection may depend on the lab running the sample. And they keep their methodology very confidential. 
Also, I'm assuming that you are talking about applying the dexamethasone topically - right on the skin. To my 
knowledge, there are no guidelines pertaining to topically applied steroids. But we do know that they are absorbed. 
 In Canada, for racehorses we have a recommendation for a 24 hour withdrawal for 20 mg of dexamethasone 
(Azium brand) given IV or IM but an Australian article I have lists 48 hrs.
> 
So what you have to do is make an educated guess on the conservative side. And rely on prevention and 
nonmedicated therapies.

>  Also, where could I find a book that
> has the withdrawal times of all the drugs listed in it?
> 

The closest thing you will find is from the racetrack organizations. In Canada, Agriculture Canada publishes a little 
book called Race Track Division Schedule of Drugs. I will try to find out where to get copies. Drug detection is a bit 
of a game between the latest rage in drugs and the ability of the labs to develop the test methodology. In AHSA, 
they allow "layering" of drugs like bute and Banamine - giving lower doses of both drugs together, keeps either 
drug from testing over the limit. At the moment, they are not testing for ketoprofen (Ketofen), a new non-steroidal 
anti-inflammatory drug.

> Can a horse compete with scratches if it's not lame?

Mine does all the time. He is extremely susceptible and it makes me crazy.

And on the Vitamin E/Selenium issue: my neighbor down the hall runs the toxicology lab for Western Canada, so I 
asked him about Vit E and selenium in our area. They actually did a study looking at over 400 horses from Alberta 
and Saskatchewan and did not identify selenium deficiences. Some horses were low in Vitamin E, mostly in the 
wintertime when on poor hay diets.

Cheers,
Trisha


Trisha Dowling, DVM, MS, Diplomate ACVIM & ACVCP
Associate Professor, Veterinary Clinical Pharmacology
Western College of Veterinary Medicine
Saskatoon, SK S7N 5B4
306-966-7359/FAX 306-966-7376