Characterization of Pharmacokinetic Parameters for Hospital Preparation of a Suppository Containing Gabapentin Tablet

Cancer pain often causes a decreased quality of life in patients. Gabapentin (GBP) is recommended as a supplementary analgesic for cancer-related pain, and can be taken at all steps of the World Health Organization pain relief ladder. However, GBP treatment is limited to oral administration. Therefore, a new route of administration is required for cancer patients who are unable to take oral medications. In this study, we demonstrate the preparation method and characterize the pharmacokinetics of a suppository containing GBP in tablet form. The suppository bases polyethylene glycol (P), Witepsol H-15 (H), and Witepsol S-55 (S) were compared to find the optimal base for the suppositories. We compared intravenous (iv), per os (po), and intrarectal (ir) administration of GBP powder and tablet formulations: (GBPp and GBPt) prepared in a base of P, H, or S (GBPp/P, GBPp/H, GBPp/S, GBPt/P, GBPt/H, and GBPt/S). The hardness of the GBPt group was significantly lower than that of the GBPp group. The drug-release profiles of the GBPt suppository groups were highest, in the order H, P, and S. The drug-release profile of the GBPt/S group was significantly higher than that of the GBPp/S group. The time to maximum drug concentration of the GBPt/S group was significantly increased compared with the po, GBPt/P, and GBPt/H groups. The GBPt/H group had similar pharmacokinetic parameters to the po group. These results suggest that a suppository containing GBP tablet is better than the conventional preparation method for hospital preparation.