The distribution of a drug in the body is influenced by several physiological properties:
1) Lipid Solubility
Highly lipid-soluble drugs (e.g., diazepam, propofol) distribute more readily into lipid-rich tissues like the brain and adipose tissue.
2) Ionization State
The ionization of a drug affects membrane permeability.
Acidic drugs accumulate in acidic tissues (e.g., stomach), while basic drugs accumulate in basic tissues (e.g., liver).
3) Molecular Size and Shape
Smaller and more compact molecules cross membranes more easily and distribute faster than larger, bulkier molecules.
4) Protein Binding
Many drugs bind to plasma proteins (e.g., albumin), limiting their availability for tissue distribution.
Only unbound (free) drugs are available for active distribution.
5) Blood Flow
Organs with high blood flow (e.g., liver, kidneys, brain) receive drugs more rapidly than low-perfusion tissues (e.g., adipose tissue).
6) Capillary Permeability
The ease with which a drug crosses capillary membranes influences its distribution.
Barriers like the blood-brain barrier (BBB) restrict drug entry, while other capillaries (e.g., in the liver) allow easier passage.
