In an attempt to improve the predictions of druglikeness, the rules have spawned many extensions, for example the Ghose filter:
* Partition coefficient log P in −0.4 to +5.6 range
* Molar refractivity from 40 to 130
* Molecular weight from 180 to 480
* Number of atoms from 20 to 70 (includes H-bond donors [e.g. OHs and NHs] and H-bond acceptors [e.g. Ns and Os])
Veber's Rule further questions a 500 molecular weight cutoff. The polar surface area and the number of rotatable bonds has been found to better discriminate between compounds that are orally active and those that are not for a large data set of compounds. In particular, compounds which meet only the two criteria of:
* 10 or fewer rotatable bonds and
* Polar surface area no greater than 140 Å
are predicted to have good oral bioavailability.