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  Discussion on Aspirin
Author Message

Posted on Friday, Apr 28, 2000 - 9:48 pm:

HI, Dr Oglesby,

I am a biology student in hight school. I also show and own quarter horses. I have been reading the Medication Menu. I have a question. I don't understand what you mean when you say" the half life of aspirin in plasma is 7 minutes and it is no longer detectable in plasma after 1 and 1/2 hours. Does this mean that the aspirin can not be detected by a blood sample after 1 and 1/2 hours? Also you state that detection time is about 2 days, so I am very confused, are these different? Does this mean that after 2 days the aspirin can be detected or does it mean that it will take 2 days for the aspirin to leave the blood stream? I would like to major in biology in regard to medications for horse, livestock and pets. Thank you for the info. Britni

Posted on Saturday, Apr 29, 2000 - 9:12 am:

Hello Debbie,
Well it is easy to see why you would be confused: the article has two apparently conflicting pieces of information. The reason is that these are taken from two different sources and they may either represent the state of detection at the time the source was written or may represent the difference between the detectability in the serum versus that found in the urine, a common way of testing for drugs on the race track.

I think it is important to understand that detectability is not only a function of the way the drug behaves in the horse but also on how sensitive the technology is and that this is getting better all the time. What was once detectable for only a day is now detectable for weeks. If drug detection may be a problem you should always use the numbers least likely to land ou in trouble.
DrO

Posted on Saturday, Apr 29, 2000 - 5:25 pm:

Hi Again,
I still don't really understand your reply, I think you said this- If you give a drug of any kind, the life of the drug in plasma can be detected for many days, even though it continues to be eliminated by the horse every so many minutes. So in the instance of aspirin, even though it is eliminated by 1/2 every 7 minutes, and even though it will be eliminated from plasma completely in 1 and 1/2 hours that it is still detectable in plasma two days later?
Is this right? And if so, how can it be detected when it's not there?
Thank you, I hope I don't sound to stupid.

Posted on Saturday, Apr 29, 2000 - 5:38 pm:

OH, just an after thought. If the aspirin leaves the blood stream by 1/2 every 7 minutes, and is completely gone in 1 and 1/2 hours, then at the 1 and 1/2 hour mark it is still in the urine. And if it is in the urine, then it would be detectable. But if a blood test was taken instead it would not be detectable. Is this right? Thanks again

Posted on Sunday, Apr 30, 2000 - 8:28 am:

Hello Debbie,
No it is not "eliminated from the blood" but 1/2 is eliminated from the blood. We speak of the 1/2 life of drugs in the blood stream because this best describes the rate of drug elimination. In theory a drug is never completely gone from the body once ingested: If you half the number of molecules every 7 minutes when the horse dies he will still have some drug in him, but what is important from a practical standpoint is how long can it be detected. I think you continue to confuse "detection in the blood" with "presence in the blood".

And yes, you are correct the detection of many (but not all) drugs is easier in the urine than the blood because the urine concentrates the drug. I am not sure however if the time given in the article was blood or urine, you should assume it is detectable in either for at least a couple of days and since that article and perhaps longer.
DrO
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