ADME is an
acronymin pharmacokineticsand pharmacologyfor absorption, distribution, metabolism, and excretion, and describes the disposition of a pharmaceuticalcompound within an organism. The four criteria all influence the drug levels and kineticsof drug exposure to the tissues and hence influence the performance and pharmacological activityof the compound as a drug:
:Before a compound can exert a pharmacological effect in tissues, it has to be taken into the
bloodstream— usually via mucoussurfaces like the digestive tract( intestinalabsorption). Uptake into the target organs or cells needs to be ensured, too. This can be a serious problem at some natural barriers like the blood-brain barrier. Factors such as poor compound solubility, chemical instability in the stomach, and inability to permeate the intestinal wall can all reduce the extent to which a drug is absorbed after oral administration. Absorption critically determines the compound's bioavailability. Drugs that absorb poorly when taken orally must be administered in some less desirable way, like intravenously or by inhalation(e.g. zanamivir).
:The compound needs to be carried to its effector site, most often via the bloodstream. From there, the compound may distribute into tissues and organs, usually to differing extents.
:Compounds begin to be broken down as soon as they enter the body. The majority of small-molecule drug metabolism is carried out in the liver by
redoxenzymes, termed cytochrome P450enzymes. As metabolism occurs, the initial (parent) compound is converted to new compounds called metabolites. When metabolites are pharmacologically inert, metabolism deactivates the administered dose of parent drug and this usually reduces the effects on the body. Metabolites may also be pharmacologically active, sometimes more so than the parent drug.
:Compounds and their metabolites need to be removed from the body via excretion, usually through the kidneys (urine) or in the feces. Unless excretion is complete, accumulation of foreign substances can adversely affect normal metabolism.
:There are three sites where drug excretion occurs. The kidney is the most important site and it is where products are excreted through urine. Biliary excretion or faecal excretion is the process that initiates in the liver and passes through to the gut until the products are finally excreted along with waste products or faeces. The last method of excretion is through the lungs e.g. anaesthetic gases.
:Excretion of drugs by the kidney involves 3 main mechanisms:::*Glomerular filtration of unbound drug.::*Active secretion of (free & protein-bound) drug by transporters e.g. anions such as urate, penicillin, glucuronide, sulphate conjugates) or cations such as choline, histamine.::*Filtrate 100-fold concentrated in tubules for a favourable concentration gradient so that it may be reabsorbed by passive diffusion and passed out through the urine.
Sometimes, the potential or real
toxicityof the compound is taken into account (ADME-Tox or ADMET). When the Liberation of the substance (from protective coating, or other excipients) is considered, we speak of LADME.
route of administrationcritically influences ADME.
Lipinski's Rule of Five
* [http://www.netsci.org/Science/Special/feature06.html The Emerging Role of A.D.M.E. in Optimizing Drug Discovery and Design]
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