Example

What is the solubility of benzylpenicillin G at a pH sufficiently low to allow only the nondissociated form of the drug to be present?

The pKa of benzylpenicillin G is 2.76 and the solubility of the drug at pH 8.0 is 0.174 mol dm 3. (From R. E. Notari, Biopharmaceutics and Pharmacokinetics, 2nd edn, Marcel Dekker, New York, 1978.)

Answer

If only the undissociated form is present at low pH then we need to find S0. This can be obtained from the information given using equation (5.11):

[OH-] Ka S0 Taking logarithms, or

0 0

Post a comment