The effects of absorption enhancers on the pulmonary absorption of recombinant human granulocyte colony-stimulating factor (rhG-CSF) in rats.

Pulmonary absorption of recombinant human granulocyte colony-stimulating factor (rhG-CSF) with various surfactants and protease inhibitors were examined in rats. The relative bioavailabilities of rhG-CSF with surfactants, such as polyoxyethylene 9-lauryl ether (Laureth-9) and sodium glycocholate (SGC), after intratracheal (i.t.) administration by intravenous (i.v.) and subcutaneous (s.c.) means were 37% (i.v.), 88% (s.c.), 84% (i.v.) and 197% (s.c.), respectively. These values were evaluated from the ratio of the area under the curve (AUC) of the plasma rhG-CSF concentration versus time for 8 h. In the presence of various kinds of protease inhibitors, such as (p-amidinophenyl) methanesulfonyl fluoride x HCl (p-APMSF), aprotinin and bestatin, an increase in the plasma rhG-CSF concentration was observed, and the effect with p-APMSF was maximal. The relative bioavailabilities of rhG-CSF with p-APMSF after i.t. administration by i.v. and s.c. means were increased about 2-fold. To clarify the absorption mechanism of rhG-CSF, rhG-CSF was intratracheally administered with both Laureth-9 and p-APMSF. The AUC of rhG-CSF increased with both agents, and was approximately equal to that with SGC, which has both an enhancing effect on membrane permeation and an inhibitory effect on enzymatic degradation after i.t. administration. Consequently, it was considered that permeation and enzymatic degradation were rate-determining steps in the pulmonary absorption of rhG-CSF after i.t. administration.