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Factors Affecting Drug Absorption: General Factors



These are the general factors that affect drug absorption by all routes.


Aqueous Solubility of the Drug

  • The drug must dissolve in aqueous biophase in order to be able to cross the biological membrane.

  • The aqueous solubility depends on:

    • Disintegration: breaking down of solid dosage form into fine particles.

    • Dissolution: dissolution of active drug molecules from fine particles into the solution.

  • The more the aqueous solubility → the faster the absorption. e.g.:

    • Tablets take time to disintegrate and dissolve → absorption from them is slower.

    • In syrup, the drug is already dissolved and ready to be absorbed → absorption from them is faster.


Concentration of the Drug

Diffusion of drug molecules is driven by concentration gradient

↓

The higher the concentration of drug

↓

The faster the absorption.


Area of Absorbing Surface

The more the absorbing surface area

↓

the more the absorption.


Blood Flow at the Absorbing Surface

Blood flow removes the absorbed drug from the site of absorption

↓

concentration gradient is maintained for absorption of more drugs

↓

so the more the blood flow

↓

the faster the absorption.

 

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