Editing Partition coefficient (section)

=== 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.<ref>{{cite book | vauthors = Bodor N, Buchwald P | title = Retrometabolic Drug Design and Targeting | date = 2012 | publisher = John Wiley & Sons, Inc. | isbn = 978-1-118-40776-9 | chapter = Chapter 2.2: Pharmacokinetic Phase: ADME | chapter-url = https://books.google.com/books?id=Hjxe9jTGUfQC&q=partition+coefficient+drug+absorption+reach+target&pg=PT38 | department = (secondary) }}</ref> Hence, the log ''P'' of a molecule is one criterion used in decision-making by [[medicinal chemistry|medicinal chemists]] in pre-clinical drug discovery, for example, in the assessment of [[druglikeness]] of drug candidates.<ref name="pmid17971784">{{cite journal | vauthors = Leeson PD, Springthorpe B | title = The influence of drug-like concepts on decision-making in medicinal chemistry | journal = Nature Reviews. Drug Discovery | volume = 6 | issue = 11 | pages = 881–90 | date = November 2007 | pmid = 17971784 | doi = 10.1038/nrd2445 | s2cid = 205476574 }}</ref> Likewise, it is used to calculate [[lipophilic efficiency]] in evaluating the quality of research compounds, where the efficiency for a compound is defined as its [[Potency (pharmacology)|potency]], via measured values of [[IC50|pIC<sub>50</sub>]] or [[EC50|pEC<sub>50</sub>]], minus its value of log ''P''.<ref>{{cite book | title = Role of Physicochemical Properties and Ligand Lipophilicity Efficiency in Addressing Drug Safety Risks | vauthors = Edwards MP, Price DA | doi = 10.1016/S0065-7743(10)45023-X | year = 2010 | pages = 381–391| volume = 45 | series = Annual Reports in Medicinal Chemistry | isbn = 978-0-12-380902-5 }}</ref>

[[File:Log P examples 01.png|thumb|upright=1.7|alt= |Drug permeability in brain capillaries (''y'' axis) as a function of partition coefficient (''x'' axis)<ref name="pmid10837718">{{cite journal | vauthors = Bodor N, Buchwald P | title = Recent advances in the brain targeting of neuropharmaceuticals by chemical delivery systems | journal = Advanced Drug Delivery Reviews | volume = 36 | issue = 2–3 | pages = 229–254 | date = April 1999 | pmid = 10837718 | doi = 10.1016/S0169-409X(98)00090-8 }}</ref>]]

==== Pharmacokinetics ====
In the context of [[pharmacokinetics]] (how the body absorbs, metabolizes, and excretes a drug), the distribution coefficient has a strong influence on [[ADME]] properties of the drug. Hence the hydrophobicity of a compound (as measured by its distribution coefficient) is a major determinant of how [[Druglikeness|drug-like]] it is. More specifically, for a drug to be orally absorbed, it normally must first pass through [[lipid bilayer]]s in the intestinal [[epithelium]] (a process known as [[transcellular]] transport). For efficient transport, the drug must be hydrophobic enough to partition into the lipid bilayer, but not so hydrophobic, that once it is in the bilayer, it will not partition out again.<ref name="Kubinyi_1979a">{{cite journal | vauthors = Kubinyi H | title = Nonlinear dependence of biological activity on hydrophobic character: the bilinear model | journal = Il Farmaco; Edizione Scientifica | volume = 34 | issue = 3 | pages = 248–76 | date = March 1979 | pmid = 43264 }}</ref><ref name="Kubinyi_1979b">{{cite journal | vauthors = Kubinyi H | title = Lipophilicity and biological activity. Drug transport and drug distribution in model systems and in biological systems | journal = Arzneimittel-Forschung | volume = 29 | issue = 8 | pages = 1067–80 | year = 1979 | pmid = 40579 }}</ref> Likewise, hydrophobicity plays a major role in determining where drugs are distributed within the body after absorption and, as a consequence, in how rapidly they are metabolized and excreted.

==== Pharmacodynamics ====
In the context of [[pharmacodynamics]] (how the drug affects the body), the [[hydrophobic effect]] is the major driving force for the binding of drugs to their [[receptor (biochemistry)|receptor]] targets.<ref name="Eisenberg">{{cite journal | vauthors = Eisenberg D, McLachlan AD | title = Solvation energy in protein folding and binding | journal = Nature | volume = 319 | issue = 6050 | pages = 199–203 | year = 1986 | pmid = 3945310 | doi = 10.1038/319199a0 | bibcode = 1986Natur.319..199E | s2cid = 21867582 }}</ref><ref name="Miyamoto">{{cite journal | vauthors = Miyamoto S, Kollman PA | title = What determines the strength of noncovalent association of ligands to proteins in aqueous solution? | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 90 | issue = 18 | pages = 8402–6 | date = September 1993 | pmid = 8378312 | pmc = 47364 | doi = 10.1073/pnas.90.18.8402 | bibcode = 1993PNAS...90.8402M | doi-access = free }}</ref> On the other hand, hydrophobic drugs tend to be more toxic because they, in general, are retained longer, have a wider distribution within the body (e.g., [[intracellular]]), are somewhat less selective in their binding to proteins, and finally are often extensively metabolized. In some cases the metabolites may be chemically reactive. Hence it is advisable to make the drug as hydrophilic as possible while it still retains adequate binding affinity to the therapeutic protein target.<ref name="Pliska">{{cite book | vauthors = Pliska V, Testa B, Van De Waterbed H   |title = Lipophilicity in Drug Action and Toxicology |publisher = John Wiley & Sons Ltd. |year = 1996 |location = New York  |pages = 439 pages |isbn = 978-3-527-29383-4 }}</ref> For cases where a drug reaches its target locations through passive mechanisms (i.e., diffusion through membranes), the ideal distribution coefficient for the drug is typically intermediate in value (neither too lipophilic, nor too hydrophilic); in cases where molecules reach their targets otherwise, no such generalization applies.{{citation needed|date=March 2016}}