Testing a new sustained-release local anesthetic formulation specifically designed for spine surgery in a sheep model

Area of Science:

• Biomaterials Science
• Anesthesiology
• Spinal Surgery

Background:

• Instrumented spinal surgery causes significant pain, often requiring opioids.
• Opioids have side effects, including dependence and addiction.
• Current non-opioid analgesics have limited duration, creating a pain management gap.

Purpose of the Study:

• To assess a hydrogel's feasibility for sustained bupivacaine delivery co-implanted with pedicle screws.
• To evaluate localized, three-day analgesia for spinal surgery pain.
• To establish an in-vivo/in-vitro release correlation (IVIVC).

Main Methods:

• A robust hydrogel loaded with bupivacaine was designed for co-implantation with pedicle screws.
• Fifteen sheep received hydrogel rings on pedicle screws (220 mg total dose).
• Wound/systemic drug levels, hydrogel degradation, and histology were assessed; IVIVC was determined.

Main Results:

• Hydrogel rings remained in place, releasing bupivacaine via first-order kinetics over 72 hours with excellent IVIVC.
• Wound fluid bupivacaine levels were 2300-fold higher than plasma levels, remaining below toxic thresholds.
• Histology showed a subsiding foreign-body response; hydrogels degraded completely within 9 months.

Conclusions:

• The developed hydrogel provides safe, localized, and sustained bupivacaine delivery.
• This technology has potential to significantly improve postoperative pain management after instrumented spinal surgery.
• It addresses the mismatch between pain duration and non-opioid analgesic efficacy.