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

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

❑ The rate and extent of absorption of a drug depend on the effective concentration

of that drug, i.e. the concentration of drug in solution in the GI fluids which is in
an absorbable form.

❑ The principal physicochemical properties that can influence the effective drug
concentration in the GI fluids are:

(A) Complexation

➢ Complexation of a drug may occur within the dosage form and/or in the GI fluids.

➢ Complexation can be beneficial or detrimental to absorption.

1. Complexes that reduce drug absorption

a-Complexation with mucin

▪ Mucin, a normal component of GI fluids, complexes with some drugs.

▪ The antibiotic streptomycin binds to mucin, thereby reducing the available
concentration of the drug for absorption. This may contribute to its poor

bioavailability.

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