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PharmD clinical pharmacy program Level 3, Semester 2 Biopharmaceutics & Pharmacokinetics (PT608(
Example: antifungal miconazole
It shows poor oral bioavailability owing to its poor solubility.
However, in the presence of cyclodextrin the solubility and dissolution rate of
miconazole are significantly enhanced.
(B). Adsorption
➢ The concurrent administration of drugs and medicines containing solid adsorbents
(e.g. antidiarrhoeal mixtures) may result in the adsorbents interfering with the
absorption of drugs from the GIT.
➢ The adsorption of a drug on to solid adsorbents such as kaolin or charcoal may
reduce its rate and/or extent of absorption, owing to a decrease in the effective
concentration of the drug in solution available for absorption.
➢ A consequence of the reduced concentration of drug in solution at the site of
absorption will be a reduction in the rate of drug absorption.
➢ Whether there is also a reduction in extent of absorption will depend on whether the
drug-adsorbent interaction is readily reversible.
➢ If the drug is not readily released from the solid absorbent in order to replace the
free drug that has been absorbed, there will also be a reduction in the extent of
absorption.
➢ Examples of interactions that give reduced extents of absorption are:
➢ Promazine – charcoal
➢ Lincomycin-kaopectate
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