Abstract
To clarify the absorption mechanism of 1, 3-bis(2-ethoxycarbonylchromon-5-yloxy)-2-((S)-lysyloxy)propane dihydrochloride (N-556), a prodrug for the oral delivery of disodium cromoglycate (DSCG), a study was made using rats. N-556 gave the highest plasma level of DSCG following its injection into the loop at the upper part of the small intestine. N-556 was stable in acidic washings of gastric contents, but rapidly hydrolyzed to M1 with twin ethyl residues on DSCG in the washings of the small intestinal contents. N-556 and M1 were hydrolyzed to DSCG via M2 having a mono ethyl residue in the homogenate of the small intestinal mucosa. The oral absorption of M1 following its administration in 50% (v/v) propylene glycol solution was essentially the same as that of N-556. That of M1 administered in aqueous suspension was low. After the oral adiministration of N-556, a small amount of M2 and a trace of M3 having L-lysyl residue were detected in the portal plasma, but no hydrolytic intermediate except DSCG could be found in the general plasma. The major absorption mechanism of N-556 may thus be concluded as follows : N-556 given orally is transferred to the small intestine in essentially intact form. N-556 is then rapidly diffused to an aqueous layer on the surface of the mucosal membrane and hydrolyzed to M1. The resultant M1 is transported to the mucosal membrane and hydrolyzed to DSCG via M2. DSCG generated in the mucosal membrane is used for general circulation through the portal blood and liver. A small amount of M2 in the mucosal membrane is transported to the portal blood and hydrolyzed to DSCG in the portal blood and/or liver to make DSCG available for the general circulation.
