ABSTRACT
After a drug or any xenobiotic gains access to the body and distributes within it, there must be some mechanism(s) whereby the molecule has its bioactivity terminated; otherwise, drug effects could last the lifetime of the recipient. For most drugs, their duration of action is inversely proportional to the rate at which they are metabolically inactivated. For example, if hexobarbital (a sedative/ hypnotic drug that can produce sleep) is given to mice and dogs, dogs will sleep, on average, 26 times longer than mice, even if they receive half the dose on a per weight basis. This increased sleeping time in dogs correlates reasonably well with the elevated half-life (time required for the blood level to decrease by one-half) of hexobarbital in that species.
