Physiological Barriers to Drug Distribution

Physiological Barriers to Drug Distribution

Certain physiological barriers regulate drug distribution, protecting tissues from harmful substances but also limiting drug access:

1. Blood-Brain Barrier (BBB)

   • Composed of tight endothelial junctions, it prevents many drugs from entering the brain.
   • Only highly lipophilic drugs or those using specialized transporters can cross.

2. Blood-Testes Barrier (BTB)

   • Protects developing sperm from harmful substances but restricts drug entry to the testes.

3. Placental Barrier

   • Separates maternal and fetal circulation, protecting the fetus from toxins but limiting drug transfer.

4. Epithelial Barriers

   • Found in the skin, respiratory tract, GIT, and urinary tract.
   • Regulates the movement of molecules but can hinder drug penetration.

5. Renal Barrier

   • Prevents loss of essential proteins while allowing waste excretion, restricting drug passage to the kidneys.

6. Hepatic Barrier

   • Limits harmful substances from entering circulation and plays a role in drug metabolism and excretion.

7. Pulmonary Barrier

   • Protects against airborne toxins while allowing gas exchange but can restrict drug absorption in the lungs.

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