AIf you mean how long is the drug effective at reducing inflammation or how long can it be detected in serum or urine, the answers are different. Also, dosage is a significant factor, as well as how many days in a row the horse is treated.

In general, phenylbutazone is administered on a 24-hour interval to maintain a fairly steady effect. If there is a noticeable response, such as a reduction in lameness, following administration of a standard dose (two grams for a 1,100-pound or 500-kg horse), then daily dosing should maintain the improvement. If this treatment continues for more than a week or 10 days, the level of the drug in the horse’s blood and urine will gradually increase.

I am assuming you want to know how often you need to give the drug to improve the horse’s well-being and control inflammation. The answer to that is daily. If, however, you seek to eliminate the drug from the horse to avoid its detection following some performance event, you need to dig deeper. In that case, there are guidelines established for the various performance events, and you should consult the agency that sponsors or regulates those events as to the dose and time to allow the level of the drug in the horse’s system to reach an acceptable level