Mechanism of drug absorption

Mechanism of drug absorption

1. Passive diffusion
2. Active transport
3. Facilitated diffusion
4. pinocytosis
5. pore transport
6. ion pair formation

1. Passive Diffusion

Passive diffusion is the most common mechanism of drug absorption. In this process, drug molecules move from an area of higher concentration to an area of lower concentration across the cell membrane without the use of energy or carrier proteins. Lipid-soluble and non-ionized drugs are absorbed more readily by this mechanism.

2. Active Transport

Active transport involves the movement of drugs across the cell membrane against their concentration gradient. This process requires energy and specific carrier proteins. It is selective and saturable. Certain drugs structurally similar to endogenous substances, such as levodopa and some vitamins, are absorbed by this mechanism.

3. Facilitated Diffusion

Facilitated diffusion is a carrier-mediated process that does not require energy. Drug molecules move along the concentration gradient with the help of specific transport proteins. Although energy is not required, this mechanism is also saturable.

4. Pinocytosis

Pinocytosis is a process in which drug molecules are engulfed by the cell membrane to form vesicles. This mechanism is mainly important for the absorption of large molecules such as proteins and some biological products.

5. Pore Transport (Filtration)

In pore transport, small water-soluble drug molecules pass through aqueous pores or channels present in the cell membrane. This mechanism is limited to drugs with small molecular size.

6. Ion Pair Formation

In this mechanism, ionized drugs temporarily combine with oppositely charged ions to form neutral complexes. These complexes are more lipid-soluble and can cross biological membranes more easily.