Studies on sustained-release suppositories. I. Effect of alginic acid addition on rectal absorption of bacampicillin in rabbits.

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Abstract
Sustained-release suppositories of bacampicillin (BAPC) were prepared by the use of the adduct which was precipitated from an aqueous solution containing BAPC and alginic acid (Alg). As the suppository base, Witepsol H-15 and macrogol were used. Absorptions of BAPC from the suppositories were prolonged in rabbits, but the bioavailabilities were decreased compared to that after administration of BAPC alone. However, these absorptions were improved enormously by the addition of surface-active agents, that is, an excellent prolonged absorption and high bioavailability were obtained. Interestingly, similar prolonged absorption could be obtained only by mixing Alg with BAPC in a suppository base. Further, this absorption rate was found to be contolled by the amount of Alg addition. The absorption profiles from a suppository containing the mixture differed from that containing the adduct in exhibiting both high plasma level and prolonged absorption. This may be due to simultaneous fast absorption of BAPC itself and formation of the adducts. Thus, it seemed that BAPC preparations containing Alg may be practically useful as a rectal preparation with prolonged action and giving a high plasma level.