An in vivo study on extended-release formulation of buprenorphine in Sprague-Dawley rats

Buprenorphine, an opium derivative, is approved as an analgesic. In this study, we aimed to evaluate the in vivo performance of an extended-release subcutaneous injection formulation of buprenorphine.

The extended-release formulation of buprenorphine was developed by Nano Daru Pharmaceutical Company to exhibit in vivo characteristics comparable to Sublocade^®. We assessed the in vivo release profile, pharmacokinetic parameters, and histopathological characteristics of the prepared formulation in Sprague-Dawley rats.

Following subcutaneous administration of the liquid formulation, a semi-solid drug reservoir was formed. The dimensions of the implant progressively diminished as a result of polymer biodegradation, with the largest size observed on Day 1 and the smallest on Day 35. A mean release of 84% of buprenorphine was observed over a 35-day period from the implant. No significant inflammatory cell infiltration was detected at the site of administration around the implants at different time points during the study period. The plasma concentration-time profile of the formulation showed an initial peak on Day 1 post-administration; buprenorphine levels then declined gradually, reaching their lowest concentration on Day 3. Subsequently, the concentration increased, reached a secondary peak, and then declined slowly thereafter.

According to the results, the plasma buprenorphine concentrations indicate sustained delivery of buprenorphine over a one-month period.