Studies on the promoting effects of carboxylic acid derivatives on the rectal absorption of .BETA.-lactam antibiotics in rats.

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Abstract
The promoting effects of sodium salts of N-acyl-L-phenylalanines, p-substituted benzoic acids, saturated straight-chain fatty acids, saturated straight-chain .alpha.-bromofatty acids and N-acyl-N-methylglycines on the rectal absorption of sodium ampicillin (ABPC Na) were investigated in rats. The absorption-promoting effect of each carboxylic acid sodium salt was parabolically correlated with its lipo-hydrophilic character (log P). The optimal log P value (log Po) of carboxylic acids exerting the maximum rectal absorption-promoting effect was in the range of 4.2.sbd.4.8. Among these carboxylic acids, sodium caprate was selected for examination of its rectal absorption-promoting action on 4 penicillins (ampicillin, sulbenicillin, piperacillin and mezlocillin) and 8 cephalosporins (cephacetrile, ceftizoxime, cephalothin, cefazolin, cefmetazole, cefotiam, cefoperazone and cefpiramide). The extents of rectal absorption of the .beta.-lactam antibiotics coadministered with sodium caprate correlated well with the permeability of the drugs to cellulose membrane.