With the aim of improving the in vivo pharmacokinetic profile after rectal administration of the standard rifampicin (RFP) suppository, a new type of suppository containing a solid dispersion of RFP was prepared and evaluated in vitro and in vivo in rats. The RFP solid dispersion was prepared by mixing RFP powder with polyethylene glycol (PEG) # 3000 or #6000 in a weight ratio of 1 : 3 to make an amorphous condition. Based on an in vitro release study on RFP, Witepsol H-32 was selected as the suppository base instead of Witepsol H-15 that is used for the standard suppository. Further, with the Witepsol H-32 suppository, the in vitro release profile of RFP for a solid dispersion in PEG #3000 (H-32/SD 30) was superior to that for a dispersion in PEG #6000 (H-32/SD 60). The area under the concentration vs. time curve (AUC) of RFP from the H-32/SD 30 suppository after rectal administration was 2.8-fold that from the standard suppository. Addition of the absorption enhancers sodium deoxycholate, sodium ursodeoxycholate and gall powder to the H-32/SD 30 suppository increased the AUC of RFP after rectal administration 1.2-fold, 1.5-fold and 1.6-fold, respectively. Moreover, the AUC for the H-32/SD 30 suppository including gall powder was 80% of the AUC in the case of orally administering the same dose of RFP to rats. The results of this study showed that our new type of RFP suppository containing an RFP solid dispersion was effective in improving RFP dissolution and bioavailability after rectal administration.
