Definition:

Rule of thumb to determine if a chemical compound has physico-chemical properties that would likely make it an orally active drug in humans.

See also: Druglikeness

The Rule of 5 claims to predict that poor absorption or permeation is more likely when there are:

  • more than 5 H-bond donors
  • 10 H-bond acceptors
  • molecular weight (MWT) greater than 500
  • calculated Log P (CLogP) greater than 5 (or Moriguchi Log P MlogP>4.15).

This hypothesis has been called into question in the case of antibiotics. Antibiotics are unique molecules and must be able to penetrate bacterial cells and not just human cells. They have always been an exception to the Lipinski rules.

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