The applicability of a gel delivery system for self-administration of buprenorphine to laboratory mice.

Oral administration of perioperative analgesia to laboratory mice is beneficial compared with administration by injection. The mice become less stressed when allowed to voluntarily ingest the drug in a palatable feed item and it results in high and long-lasting serum concentrations of the drug. We have previously demonstrated sticky nut and chocolate paste to be well-liked by mice and readily ingested in most cases. However, a disadvantage with nut and chocolate paste is its high content of fat and sugar, which may have undesirable effects in some experimental models. Alternatively, a delivery system using an aqueous gel may serve as a supplementary source of fluid post-operatively and as a vehicle for analgesic drugs. In the present study, we investigated the willingness of the mice to ingest a commercially available gel, by measuring the duration from introduction of the gel to first ingestion, as well as the amount ingested overnight. Furthermore, buprenorphine in two different concentrations (5 and 15 µg/mL) was mixed in the gel and the resulting serum concentrations of buprenorphine were investigated. The aqueous gel was ingested by the mice, but their willingness was low and did not increase over time. The serum concentrations of buprenorphine were similar to, or higher than, those following a subcutaneous injection (0.1 mg/kg body weight), but the variation was considerably higher. In conclusion, aqueous gel may serve as a relevant vehicle for the voluntary ingestion of buprenorphine in mice, but the willingness of the mice to ingest the gel needs to be improved.