Distribution of drugs

Distribution of drugs

Definition(Distribution of drug): All the consequences of delivery of drugs to the tissue is called distributation of drug.

Selective distribution of drug: It means special distribution of drug in the certain tissue of the body due to special affinity between particular drug & particular body constituents.

Example:       

  • Chloroquine=Melanin containing tissue(retina).
  • Ephidrine=Iris.
  • Chlorpromazine=Brain.
  • Guanethidine=Heart & skeletal muscle.
  • Digoxin=Heart.

Factors modifying distribution of drug:

Physio-chemical properties of drug:

  • Lipid soluble drug→both intracellular & extracellularly.Mainly intracellularly can cross blood brain barrier.
  • Water soluble drug→Extracellular distributation.
  • Polar or ionized drug→↓Lipid soluble→More extracellular distribution.

Plasma protein binding of drug:

  • Acidic & netural drugs mostly blind with albumin.
  • Basic drugs mostly bind with lipoprotein & α1 acid glycoprotein.
  • Hormone such as steroids,thyroid etc blind with globulin.

Cellular binding of drug:Certain drugs have special affinity for certain tissue & they exist in high conc.Compared to plasma.This phenomenon is called cellular reservoir of drug & tissue are called selective reservoir.e.g

  • Choloroquine→Melanin containing tissue(retina).
  • Tetracycline→containing tissue(Bone & teeth).

Blood placental barrier:The placental membrane which separates maternal & foetal blood.It consists of 4 layers:

  • Endothelial lining of foetal vessels.
  • Connective tissue of villus core.
  • Cytotrophoblastic layer.

Blood brain barrier:The selective barrier between the blood & the brain tissue is known as blood brain barrier.

Structure forming the blood brain barrier:

  • The endothelial cells in the wall of the capillary.
  • A continuous basement membrane.
  • The foot processes of astrocytes.

Cardiac output/Regional blood flow:

  • ↑Blood flow (e.g brain,heart,liver,Kidney)→↑ distribution.
  • ↓Blood flow (e.g muscle,adipose tissue)→↓ distribution.

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