There are various databases that provide the physical and chemical properties of the drug. Two of the most common links are given below:
✶ Log P
Log P refers to the lipophilicity of the drug. It is the logarithmic value of the partition coefficient between oil/octanol and water. A higher log P indicates a greater distribution of the drug into organs and tissues.
✶ Log D
D refers to distribution coefficient. Unlike log P, which is independent of pH, log D appropriately describes the distribution of ionizable compounds as this measure is pH dependant.
The pH of a drug solution indicates whether the drug is an acid (pH < 7) , base (pH > 7) or a neutral (pH = 7) compound. A monoprotic acid has one H⁺ in excess to donate and a diprotic has two. Similarly for bases, they have excess OH⁻ ions. A zwitterionic compound has equal number of H⁺ and OH⁻ ions. A neutral compound does not ionize and has a net charge of zero. Note: For monoprotic compounds, only the value in pKa1 is considered, pKa2 is allocated a value of zero. For zwitterions, acidic pKa should be entered in pKa1 box and the basic in pKa2.
pKa is the logarithmic value of the acid dissociation constant i.e. measure of the strength of acid in solution. A small pKa value for an acidic
compound indicates a strong acid and vice versa. The model at present can take an input of only two pKa values.
Note: For zwitterions, please enter the acidic pKa in pKa1 and in pKa2 for the base.
✶ Protein binding
The amount of drug bound to the plasma proteins (albumin, fibrinogen etc.). The higher the percent bound, the slower the elimination rate. The value should be entered as percentage bound to proteins.
✶ Blood-to-plasma ratio
This is the ratio of drug concentration in whole blood compared to its concentration in plasma.