The amount of an orally taken drug that makes it to the site in the body at which it exerts its effects is much lower than the amount of an intravenously administered drug and it varies considerably between individuals. One reason for this is that a substantial proportion of more than half of all orally prescribed medications are broken down in the intestine and liver, by an enzyme known as CYP3A, before reaching their site of action (a process known as first-pass metabolism). In a new study, Alfred Schinkel and colleagues from The Netherlands Cancer Institute, have developed a new mouse model for predicting the loss in available drug due to metabolism by CYP3A.
