Diazepam (DPM) suppositories are effective in the treatment of febrile convulsions in children, and acetaminophen (AAP) suppositories are used for antipyretics in combination. When DPM and AAP suppositories are administered at the same time, the absorption ratio of DPM is reduced because DPM dissolves in the oil base in the AAP suppository. Therefore, the AAP suppository is administered 30 min after the administration of the DPM suppository in clinical practice. In the present study, improvement against the absorption reduction of DPM was performed by delaying the DPM melting by the AAP suppositories. We specifically investigated the feasibility of simultaneous administration of the DPM suppository and AAP suppository by coating the AAP suppositories with purified shellac.

The flow-through cell tube method was used to measure the drug release from each suppository. The suppository combinations used in the release study were DPM suppository alone, AAP suppository alone, a combination of DPM suppository + AAP suppository, and a combination of DPM suppository + shellac-coated AAP suppository (shellac-coating concentration:1.5%, 3.0%, 5.0%). Both DPM and AAP showed decreased absorption when the both DPM suppository and AAP suppository were taken at the same time. DPM absorption improved when taking the DPM suppository and shellac-coating AAP suppository at the same time. However, the high coating amount of purified shellac reduced the AAP release. Thus, the coating amount of purified shellac was considered best at 1.5%.

These results suggested that the DPM suppository and AAP suppository can be administered simultaneously by coating the AAP suppository with purified shellac.