The "Rule of 5" by Lipinski et al can help identify a drug that is likely to have poor absorption or intestinal permeability. The rules are based on the chemical characteristics of the drug.
Poor absorption is likely if:
(Rule 1) The number of H-bond donors > 5.
(Rule 2) The number of H-bond acceptors > 10.
(Rule 3) The molecular weight of the drug > 500.
(Rule 4) The log P > 5.
Exception (Rule 5): Compound class that is a substrate for a biological transporter.
where:
• The number of H-bond donors is expressed as the sum of OHs and NH3s.
• The number of H-bond acceptors is expressed as the sum of Ns and Os.
• Log P is the solvent to water partition coefficient, typically for 1-octanol to water. This is a measure of lipophilicity (page 36).
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