Duration of absorption-enhancing effect of sodium octanoate, sodium hexanoate or glycery-1-monooctanoate on rectal absorption of gentamicin in rabbits.

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Abstract
The duration of the absorption-enhancing effect of sodium octanoate (C8), sodium hexanoate (C6) and glyceryl-l-monooctanoate (MO) on the rectal absorption of gentamicin (GM) using the hollow-type suppository was investigated in rabbits. To evaluate the duration of the absorption-enhancing effect by pretreatment (treatment of absorption enhancer before GM administration), suppository I containing each absorption enhancer in the cavity was administered into the rectum. Then suppository II containing GM in the cavity was administered at predetermined times (0.33, 2, 6 and 24 h) after the administration of suppository I. Plasma GM levels obtained by the pretreatment with absorption enhancer were compared with those obtained by the simultaneous administration of GM with absorption enhancer. The AUC and Cmax of GM significantly decreased with the pretreatment of C8 (6 and 24 h), C6 (2 and 6 h) or MO (6 and 24 h) before rectal GM administration, as compared with the simultaneous administration of GM with C8, C6 or MO. A marked decrease in the absorption-enhancing effect of C8, C6 and MO on rectal GM absorption was observed by the prolongation of the period between the pretreatment of each absorption enhancer and GM administration. The duration of the absorption-enhancing effect of C6 was shorter than that of C8, whereas this duration of MO was similar to that of C8. The effect of these absorption enhancers disappeared 24 h after the pretreatment. These results suggested that the lowering of the membrane transport barrier function recovered about one day after the administration of C8 or MO.