Distribution in pharmacology is a branch of pharmacokinetics which describes the reversible transfer of a drug from one location to another within the body.
Once a drug enters into systemic circulation by absorption or direct administration, it must be distributed into interstitial and intracellular fluids.
The drug is easily distributed in highly perfused organs such as the liver, heart and kidney.
It is distributed in small quantities through less perfused tissues like muscle, fat and peripheral organs.
There are many factors that affect a drug's distribution throughout an organism, but Pascuzzo[1] considers that the most important ones are the following: an organism's physical volume, the removal rate and the degree to which a drug binds with plasma proteins and / or tissues.
It can be defined as the theoretical volume that a drug would have to occupy (if it were uniformly distributed), to provide the same concentration as it currently is in blood plasma.
is equivalent to the dose of the drug that has been administered the formula shows us that there is an inversely proportional relationship between
This gives an indication of the importance of knowledge relating to the drug's plasma concentration and the factors that modify it.
This concept is of clinical interest as it is sometimes necessary to reach a certain concentration of a drug that is known to be optimal in order for it to have the required effects on the organism (as occurs if a patient is to be scanned).
[1] This new concept builds on earlier ideas and it depends on a number of distinct factors: Some drugs have the capacity to bind with certain types of proteins that are carried in blood plasma.
This is important as only drugs that are present in the plasma in their free form can be transported to the tissues.
The binding between a drug and plasma protein is rarely specific and is usually labile and reversible.
On the other hand, at binding rates of greater than 95% small changes can cause important modifications in a drug's tissue concentration.
Perhaps the most important plasma proteins are the albumins as they are present in relatively high concentrations and they readily bind to other substances.
Other important proteins include the glycoproteins, the lipoproteins and to a lesser degree the globulins.
Later, less vascular but more bulky tissues (such as muscle and fat) take up the drug—plasma concentration falls and the drug is withdrawn from these sites.