Lipinski's rule of five

Etymology
The rule was formulated by Christopher A. Lipinski in 1997. Five refers to the multiples of five that occur in all of the criteria.

Proper noun

 * 1)  A rule of thumb stating that a chemical compound is likely to be an orally active drug in humans unless it violates more than one of these criteria: (i) no more than 5 hydrogen bond donors (the total number of nitrogen–hydrogen and oxygen–hydrogen bonds); (ii) no more than 10 hydrogen bond acceptors (all nitrogen or oxygen atoms); (iii) a molecular mass less than 500 daltons; (iv) an octanol-water partition coefficient (log P) that does not exceed 5.