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.
- Chloroquine=Melanin containing tissue(retina).
- Guanethidine=Heart & skeletal muscle.
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.