Distribution (pharmacology)
Encyclopedia
Distribution in pharmacology
is a branch of pharmacokinetics
which describes the reversible transfer of drug from one location to another within the body.
The distribution of a drug between tissues is dependent on permeability
between tissues (between blood and tissues in particular), blood flow and perfusion
rate of the tissue and the ability of the drug to bind plasma proteins and tissue. pH parturition
plays a major role as well.
Once a drug enters into systemic circulation by absorption or direct administration, A drug has to be distributed into interstitial and intracellular fluids.The lipid solubility, pH of compartment, extent of binding with plasma protein and tissue proteins, cardiac output, regional blood flow, capillary permeability are associated for distribution of the drug through tissues.The drug is easily distributed in highly perfused organs like liver, heart, kidney etc. in large quantities & in small quantities it is distributed in low perfused organs like muscle, fat, peripheral organs etc. The drug can be moved from the plasma to the tissue until the equilibrium is established (for unbound drug present in plasma).
The volume of distribution
(VD) of a drug is a property that quantifies the extent of distribution.
Redistribution
Highly lipid soluble drugs given i.v or by inhalation initially get distributed to organs with high blood flow, e.g. Brain, heart, kidney,etc.
Later, less vascularbut more bulky tissues (muscle,fat) take up the drug—plasma concentration falls & the drug is withdrawn from these sites. If the site of action of the drug was in one of the highly perfused organs, redistribution results in termination of the drug action.
Greater the lipid solubility of the drug, faster is its redistribution.
Anaesthetic action of thiopentone is terminated in few minutes due to redistribution. However when the same drug is given repeatedly or continuously,over long periods, the low perfusion, high capacity sites get progressively filled up and the drug becomes longer acting.
Pharmacology
Pharmacology is the branch of medicine and biology concerned with the study of drug action. More specifically, it is the study of the interactions that occur between a living organism and chemicals that affect normal or abnormal biochemical function...
is a branch of pharmacokinetics
Pharmacokinetics
Pharmacokinetics, sometimes abbreviated as PK, is a branch of pharmacology dedicated to the determination of the fate of substances administered externally to a living organism...
which describes the reversible transfer of drug from one location to another within the body.
The distribution of a drug between tissues is dependent on permeability
Vascular permeability
Vascular permeability, often in the form of capillary permeability, characterizes the capacity of a blood vessel wall to allow for the flow of small molecules or even whole cells in and out of the vessel. Blood vessel walls are lined by a single layer of endothelial cells...
between tissues (between blood and tissues in particular), blood flow and perfusion
Perfusion
In physiology, perfusion is the process of nutritive delivery of arterial blood to a capillary bed in the biological tissue. The word is derived from the French verb "perfuser" meaning to "pour over or through."...
rate of the tissue and the ability of the drug to bind plasma proteins and tissue. pH parturition
PH parturition
pH partition is the tendency for acids to accumulate in basic fluid compartments, and bases to accumulate in acidic compartments. The reason for this phenomenon is that acids become negatively electric charged in basic fluids, since they donate a proton. On the other hand, bases become positively...
plays a major role as well.
Once a drug enters into systemic circulation by absorption or direct administration, A drug has to be distributed into interstitial and intracellular fluids.The lipid solubility, pH of compartment, extent of binding with plasma protein and tissue proteins, cardiac output, regional blood flow, capillary permeability are associated for distribution of the drug through tissues.The drug is easily distributed in highly perfused organs like liver, heart, kidney etc. in large quantities & in small quantities it is distributed in low perfused organs like muscle, fat, peripheral organs etc. The drug can be moved from the plasma to the tissue until the equilibrium is established (for unbound drug present in plasma).
The volume of distribution
Volume of distribution
The volume of distribution , also known as apparent volume of distribution, is a pharmacological term used to quantify the distribution of a medication between plasma and the rest of the body after oral or parenteral dosing...
(VD) of a drug is a property that quantifies the extent of distribution.
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Redistribution
Highly lipid soluble drugs given i.v or by inhalation initially get distributed to organs with high blood flow, e.g. Brain, heart, kidney,etc.
Later, less vascularbut more bulky tissues (muscle,fat) take up the drug—plasma concentration falls & the drug is withdrawn from these sites. If the site of action of the drug was in one of the highly perfused organs, redistribution results in termination of the drug action.
Greater the lipid solubility of the drug, faster is its redistribution.
Anaesthetic action of thiopentone is terminated in few minutes due to redistribution. However when the same drug is given repeatedly or continuously,over long periods, the low perfusion, high capacity sites get progressively filled up and the drug becomes longer acting.