After absorption, drugs distribute to tissues and fluids, with lipid-soluble drugs achieving wider distribution. The extent of distribution depends on lipid solubility, ionization, and binding to plasma and tissue proteins. Apparent volume of distribution is defined as the volume needed to provide the measured plasma concentration based on the administered dose, and depends on factors like lipid solubility and plasma protein binding, with more lipid-soluble and protein-bound drugs having a lower apparent volume of distribution. Highly lipid-soluble drugs given intravenously initially distribute to organs with high blood flow like the brain, heart, and kidneys.

2. DISTRIBUTION:
 After a drug is absorbed, it is distributed to various body
tissues and fluids. Drug which easily pass through cell
membrane achieve wide distribution.
 Drugs which do not pass through cell membrane are
limited in their distribution.
 If it gets distributed to other tissues that initially had no
drug, concentration gradient being in the direction of
plasma to tissues.

3.  Extent of drug distribution depends on following
 Lipid solubility
 Ionization
 Extent of binding to plasma and tissue Proteins'.
 Apparent volume of distribution defined as volume
into which the total amount of drug in the body
appears to be uniformly distributed to provide the
concentration of the drug actually measured in the
plasma calculated by Dose administered
I.V/Plasma concentration.
 E.g. Vd=1000/50=20L.

4.  Lipid soluble drugs do not enter into cells.
 Vd=ECF
 E.g. Streptomycin ,Gentamycin is 0.25L/KG.
 Drugs with high lipid soluble and plasma protein
binding remain in vascular compartment and have low
Vd value. E.g. Phenylbutazone and warfarin
vd=0.1L/KG.
 In the case of poisoning drug with large volume of
distribution not easily removed by haemodialysis.

5.  Redistribution: Highly lipid soluble drugs given I.V or
inhalation initially get distributed to organs with high
blood flow. E.g. brain, heart, kidney etc.
