Diffusion through lipid membrane

Basic terms to get things into head:-


Diffusion:-                   

Typically a random motion of molecules the net movement takes place from a region of high concentration to a region of low concentration.

Permeability coefficient:- 

Number of molecules crossing the membrane per unit area in unit time.

Partition coefficient :-

The measure of lipid solubility i.e. (hydrophobicity/lipophilicity) in a drug, a high partition coefficient substance states that it is more lipophilic.

Non-polar molecules which freely occurs in the lipid membrane continuously diffuse across the cell-membrane ,the number of molecules diffusing through the membrane depends on permeability coefficient(P) and also on concentration gradient. Permeant molecules must be present within the membrane in sufficient numbers and must be mobile within the membrane if rapid permeation is to occur. Two physicochemical factors contribute to P, namely solubility in the membrane  and diffusivity, which is a measure of the mobility of molecules within the lipid and is expressed as a diffusion coefficient (diffusion coefficient varies only modestly between conventional drugs).







In case of drug A the transmembrane concentration gradient is more than drug B(lipid insoluble)   the small molecules or drug molecules diffuses rapidly.














Comments

Post a Comment

Popular posts from this blog

A for Absorption !

Image
Absorption is the movement of drug from its site of administration into the circulation. Not only the fraction of the administered dose that gets absorbed, but also the rate of absorption is important.  Routes of drug administration and absorption of drugs (sr: Rang and Dale's Pharmacology) Except when given intravenous, the drug has to cross biological membranes. Other factors influencing absorption are: Aqueous solubility : Drugs given in the solid form must dissolve in aqueous biophase before they are absorbed. A drug given as watery solution is absorbed faster.  Concentration : Passive diffusion depends on concentration gradient : concentrated drug solution is absorbed faster. Area of absorbing surface : Larger it is, faster the absorption. Vascularity of the absorbing surface : Blood circulation removes drug from site of absorption and maintains concentration gradient. Route of administration : Main routes include oral, sublingual, rectal, topical application, inhalat...
Read more

TESTING FOR TOXICITY,MUTAGENICITY & GENOTOXICITY

Image
Testing for Toxicity Both short-term or acute and long-term or chronic toxicity testing are carried out to determine the toxic effects of the drug and mortality in animal models.All these tests are carried out under a standard procedure of "GOOD LABORATORY PRACTICE" to safeguard the quality, integrity, and safety of the preclinical trials.  Drug Development: Drugs must be approved by the FDA before they can be marketed in the US.  Long, costly, and inherently risky: only 1 of 10-15,000 reach FDA approval.  Toxicology testing is required to demonstrate that drugs are safe before they can be given to humans. Testing of Mutagenicity:- Mutagenicity :- Mutagenicity refers to the induction of permanent transmissible changes in the amount or structure of the genetic material of cells or organisms. These changes may involve a single gene or gene segment , a block of genes or chromosomes. Testings: - Carcinogenicity:- Ames test   is used as one of the initial screen...
Read more

EVOLUTION OF DRUGS

Image
  Definition  Berries of coffee plant     A drug is defined as any chemical agent that affects the living protoplasm. Drug invention vs Drug discovery A drug discovery is not intentional. A drug invention   is defined as the intentional process Poisonous mushroom by which the drug is sculpted by experimentation &   optimization of individual properties .  Early experiences in chemistry Goats went insane after eating the berries of coffee plant  Professional poisoners used mushrooms and Belladona  Atropa belladona source: www.fs.fd.usa Curare was used by South American tribes for hunting Poppy  was used to relieve pain Chinese herb Ma Huang was used as a circulatory stimulant Rise of Organic chemistry PAUL EHLRICH worked on dyes  He invented arsphenamine named as  Salvarsan - Salvation of humankind  PAUL EHLRICH Father of chemotherapy curare   poppy                 ...
Read more