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PARTITION COEFFICIENT

This document discusses the determination of partition coefficients of drug molecules and its importance in preformulation studies. The partition coefficient is the ratio of concentrations of a compound between two immiscible liquids, such as octanol and water, at equilibrium. It is a measure of how hydrophilic or lipophilic a compound is. Determining the partition coefficient provides useful information for developing stable and bioavailable dosage forms as it influences a drug's absorption and distribution in the body. Common methods to determine the partition coefficient include the shake flask method and HPLC. The coefficient affects pharmacokinetic properties like ADME and is an important consideration in preformulation to optimize drug delivery.

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DETERMINATION OF PARTITION COEFFICIENT OF A DRUG MOLECULE AND ITS APPLICATION IN PREFORMULATION STUDIES MOUMITA BANERJEE 24201911013 B.PHARMA 4TH YEAR UNDER GUIDANCE OF:- MR. P.K.DUTTA
WHAT IS PARTITION COEFFICIENT In the Chemical and Pharmaceutical Sciences a partition coefficient is the ratio of concentrations of a compound in the two phases of a mixture of two immiscible liquids at equilibrium. The partition coefficient is a ratio of concentrations of un-ionized compound between the two liquid phases. The logarithm of the ratio of the concentrations of the un-ionized solute in the solvents is called log P: When one of the solvents is water and the other is a non-polar solvent, then the log P value is also known as a measure of lipophilicity. For example, in an octanol-water system:
WHY IS IT REQUIRED TO DETERMINE IN PREFORMULATION STUDIES • It describes the process of optimizing the delivery of drug thorough determination of physical, chemical properties of new drug molecule that affect drug performance and development of an efficacious stable and safe dosage form. • Preformulation studies on a new drug molecule provide useful information for subsequent formulation of a physicochemically stable and bio-pharmaceutically suitable dosage form
METHODS OF DETERMINATION OF PARTITION COEFFICIENT OF A DRUG MOLECULE Shake flask (or tube) method HPLC determination Electrochemical methods
APPLICATIONS 1. Pharmacology - A drug's distribution coefficient strongly affects how easily the drug can reach its intended target in the body, how strong an effect it will have once it reaches its target, and how long it will remain in the body in an active form. 2. Pharmacokinetics - In the context of pharmacokinetics (what the body does to a drug), the distribution coefficient has a strong influence on ADME properties of the drug. 3. Pharmacodynamics - In the context of pharmacodynamics (what a drug does to the body), the hydrophobic effect is the major driving force for the binding of drugs to their receptor targets. 4. Consumer products - Many other industries take into account distribution coefficients for example in the formulation of make-up, topical ointments, dyes, hair colours and many other consumer products. 5. Agrochemicals - Hydrophobic insecticides and herbicides tend to be more active. Hydrophobic agrochemicals in general have longer half lives and therefore display increased risk of adverse environmental impact. 6. Metallurgy - In metallurgy, the partition coefficient is an important factor in determining how different impurities are distributed between molten and solidified metal. It is a critical parameter for purification using zone melting, and determines how effectively an impurity can be removed using directional solidification, described by the Scheil’s equation. 7. Environmental - The hydrophobicity of a compound can give scientists an indication of how easily a compound might be taken up in groundwater to pollute waterways, and its toxicity to animals and aquatic life. Partition coefficient can also used to predict the mobility of radionuclides in groundwater.
HOW IT RELATES TO DRUG ABSORPTION • Drug absorption is determined by the drug's physicochemical properties, formulation, and route of administration. • In the physical sciences, a partition-coefficient (log P) or distribution-coefficient (log D) is the ratio of concentrations of a compound in a mixture of two immiscible phases at equilibrium. These coefficients are a measure of the difference in solubility of the compound in these two phases. • Partition coefficient significances how and what extent the drug will dissociate and then cross the cellular barrier to what extent of absorption. Since drug absorption depends on the chemical nature of the drug molecule as well as the absorption site media pH and other buffering environment, the key role of partition coefficient is to ensure and maintain or perform the absorption in adequate proportion within selective biological environment. For instance, to obtain the absorption of a lipophilic drug there should be a fatty medium where the ratio of the drug to be designed to be more hydrophobic to cross the barrier, lipid> water=1.
RELATION WITH INTESTINAL pH
RECENT STUDIES OF PARTITION COEFFICIENT IN NEW DRUG MOLECULE 1. Relationship of octanol/water partition coefficient and molecular weight to rat brain capillary permeability 2. Estimation of blood-brain barrier crossing of drugs using molecular size and shape, and H-bonding descriptors 3. Fluorine in medicinal chemistry 4. Quantitative approach to biochemical structure-activity relationships 5. Caco-2 monolayers in experimental and theoretical predictions of drug transport 6. IAM chromatography: an in vitro screen for predicting drug membrane permeability
CONCLUTION Preformulation studies on a new drug molecule provide useful information for subsequent formulation of a Physicochemically stable and Biopharmaceutically suitable dosage form. Thorough Preformulation work is the foundation of developing efficacious and economical formulations.
REFERENCES • Ansel’s Pharmaceutical Dosage forms and Drug Delivery Systems, 8th Edition, Loyld V.Allen, Jr. Nicholas G. Popovich Howor, DC.Ansel • The Theory and Practice of Industrial Pharmacy, Leno lachman, Herbert A.Lieberman, Special Indian Edition 2009, CBS Publishers and Distributers Pvt. Ltd. • http://cdn.intechopen.com/pdfs-wm/28116.pdf • http://lab-training.com/landing/aqueous-solubility/ • http://www.academia.edu/7720904/CHAPTER_1_Preformulation_Studies • http://www.pharmainfo.net/reviews/preformulation-need-dosage-form- design • http://www.slideshare.net/manoj2205/solubility-and-partition-coefficient • www.Wikipedia.com
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