Physico-chemical properties of the active metabolites of the isoxazolylpenicillins as deduced from their chromatographic behaviour.

Reversed-phase chromatography of the active metabolites of the isoxazolylpenicillins revealed that the metabolites of oxacillin, cloxacillin, and dicloxacillin have the same fractional increase in hydrophilicity. The metabolite of flucloxacillin showed a much lesser decrease in lipid solubility. Regarding the relationship between the free-energy related hydrophobicity parameter pi and structure, it is concluded that the biotransformation of the isoxazolylpenicillins results in the same structural alteration of oxacillin, cloxacillin, and dicloxacillin. Flucloxacillin is handled differently by the drug metabolizing systems.