Dr. Li Partition

define partition/distribution coefficient

its the measure of the ability of a compound to distribute in two immiscible phases

what does this equation defined as?

defined as the partition/ distribution coefficient

define partition coefficient

distribution of an unionized compound between two immiscible liquid phases at equilibrium

often expressed as Log P or K

what do these equations signify?

partition coefficients

what happens when log = 0?

equally soluble in water and partition solvent

what happens when log is = 1 or higher (+) numbers?

more soluble in partition solvent

what happens when log is = -1 or any (-) numbers?

more soluble in water

how do you determine partition coefficient?

• typically in octanol and water

• some other solvents used for organic phase

  • chloroform, ether, hexane

what is the partitioning of weak electrolytes?

• expression of partition coefficient is valid for non-electrolytes

• expression of distribution coefficient takes ionized species into account

  • liquid phase only unionized form of drug

  • aqueous phase contains both ionized and unionized form of drug existing in equilibrium

what does this equation identify?

partitioning of weak electrolytes

what does this equation identify?

partition of weak electrolytes between organic and aqueous phase

[HA]w in water ionizes to [H+] + [A-]

what does this equation identify?

partition of weak electrolytes between organic and aqueous phase

what does this equation identify?

partition of weak electrolytes between organic and aqueous phase

what does this equation identify?

partition of weak electrolytes between organic and aqueous phase

what is K and D

• distribution constant

• same for unionized compound

• K relates to unionized or neutral compounds

• D is only used for ionizable compounds

• D is pH dependent

what is extraction?

the efficiency with which one solvent extracts a compound from another immiscible solvent is dependent upon the distribution and is used in

• isolation of pure compounds from crude mixtures

• separation of analytes from plasma samples during pharmacokinetic studies

what does this equation refer to?

extraction

W and W1 = weight of solute added

V1 and V2 are volumes of extracting and original solvents

what is multiple extraction?

• extraction efficiency can be improved by extracting multiple times using same volume of extracting solvent

what is the range for good oral absorption?

logP = 0-3

what does it mean when you have a high logP (log P > 4)

retained in lipophilic region, e.g. deposit in cellular membrane or fatty issue

what does is mean for a low log P?

highly water soluble and poor permeation across biological membrane