Page 103 - Interactive Theoritical Notes of Bioharmaceutics and pharamcokinetics.docx compressed

PharmD clinical pharmacy program Level 3, Semester 2 Biopharmaceutics & Pharmacokinetics (PT608(

ii- Physicochemical and dosage form factors affecting drug absorptions

❑ For a drug to be absorbed it needs to be in solution and, secondly, to pass

across the membrane (the gastrointestinal epithelium).

❑ The physicochemical properties of the drug that will influence

bioavailability can be classified as follows:

I. Factors affecting the dissolution rate

II. Factors affecting the concentration of drug in solution in the GI fluids

III. Factors affecting passage of drug through GI membranes

1. Factors affecting the dissolution rate

(A). Solubility and dissolution

❑ Solid drugs need to dissolve before they can be absorbed
.
❑ The transfer of molecules or ions from a solid state into solution is known as

"dissolution".

❑ "Solubility" of a substance is the amount of it that passes into solution when

equilibrium is established between the solution and excess (undissolved) substance.

The solution that is obtained under these conditions is said to be saturated.

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