Abstract: Pharmaceutical compositions with heretofore unknown and enhanced physical, chemical, and biological properties are prepared by combining known biologically active parent compounds with oxo thia azabicyclo compounds, such as lactam and .beta.-lactam compounds, capable of rapidly transporting the parent compounds in undegraded form to their target sites of action. A process for combining the parent compound with .beta.-lactam compounds consists of dissolving the parent compound in a polar solvent, adding a .beta.-lactam compound, incubating the resulting mixture, followed by drying, and subjecting the remaining solid material to solvent washing or extraction to further purify the new pharmaceutical composition. The new pharmaceutical composition possesses the biological and therapeutic activity of the parent compound and the barrier penetrating characteristics of the .beta.