Page 125 - Interactive Theoritical Notes of Bioharmaceutics and pharamcokinetics.docx compressed

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

1. Solutions

 Drugs are generally absorbed more rapidly from solution.

 The rate-limiting step is likely to be gastric emptying, particularly when the drug

is administered after meals.

 However, dilution of an aqueous solution may result in precipitation in the

following cases:

1. Poorly water-soluble drug whose aqueous solubility had been increased by

formulation techniques such as cosolvency, complex formation or solubilization

can result in precipitation of the drug in the gastric fluids.

2. Exposure of an aqueous solution of a salt of a weak acidic compound to gastric

pH can also result in precipitation of the free acid form of the drug.

 In most cases the extremely fine nature of the resulting precipitate permits a

more rapid rate of dissolution than if the drug had been administered in other

types of oral dosage forms, such as suspension, hard gelatin capsule or tablet.

2. Suspensions

 A well-formulated suspension is second to a solution in efficiency of absorption.

 Dissolution is the rate-limited factor in absorption of a drug from a suspension.

 However, drug dissolution from a suspension can be rapid if very fine or

micronized powders are used. (These have a larger surface area or specific

surface.)

3. Capsules

 Unlike the tablets, drug particles in a capsule are not subjected to high

compression forces, which tend to compact the powder or granules and reduce

the effective surface area.

 Hence, upon disruption of the shell, the encapsulated powder mass should

disperse rapidly to expose a large surface area to the GI fluid.

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