Distribution (pharmacology)

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 (V_D) of a drug is a property that quantifies the extent of distribution.

External links

Distribution of Drugs

Medication > Pharmacology

Pharmacokinetics	ADME: Absorption • Distribution • Metabolism • Excretion (Clearance) Loading dose • Volume of distribution (Initial) • Rate of infusion Compartment • Bioequivalence • Bioavailability Onset of action • Biological half-life • Plasma protein binding Therapeutic index (LD₅₀/ED₅₀)

Pharmacodynamics	Toxicity (Neurotoxicology) • Dose-response relationship (Efficacy, Potency) Antimicrobial pharmacodynamics: Minimum inhibitory concentration/Bacteriostatic • Minimum bactericidal concentration/Bactericide

Agonism and antagonism	Agonist: Inverse agonist • Irreversible agonist • Partial agonist • Superagonist • Physiological agonist Antagonist: Competitive antagonist • Irreversible antagonist • Physiological antagonist Other: Binding • Affinity • Binding selectivity • Functional selectivity

Other	Drug tolerance: Tachyphylaxis Drug resistance: Antibiotic resistance • Multiple drug resistance

Related fields/subfields	Pharmacogenetics • Pharmacogenomics • Neuropsychopharmacology (Neuropharmacology, Psychopharmacology)

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.