Dear Khalid: to my understanding, there is no reliable equation or formula in use to answer your question. However, you know that the dose of medicine is important, so it is related proportionally to weight, mg/kg. Then, after that test on animals, you should do the next step on human and, on that sample, you will realize how long time you need to recommend that drug to human. Wish you luck.
First, the nature of the drug matters because there are different excretion mechanisms. Some animals lack such pathways. Some drugs that are used in vet. practice is toxic to humans and vise versa.
Second consider the bioavailability, plasma level, and clearance time (half-life).