Extending local anesthetic effects with low‐dose adjuvants

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In a recent continuing education session at Fetch Nashville 2025, Mike Barletta, DVM, MS, PhD, DACVAA; Tasha McNerney, CVT, CVPP, VTS (Anesthesia & Analgesia); and Kristen Ward, BSN-RN, RVT, VTS discussed the clinical value of prolonging local anesthetic effects by incorporating low-dose adjuvants in their session titled “Top 7 Local Blocks for Everyday Practice.” Part of their discussion included the use of 3 primary adjuvants—dexmedetomidine, epidural morphine, and buprenorphine—each of which can be integrated into existing local anesthetic regimens to achieve prolonged analgesia and potentially reduce perioperative opioid requirements.

Dexmedetomidine as a peripheral adjuvant

Barletta described adding dexmedetomidine at a concentration of 1 µg/mL of local anesthetic (eg, 5 µg in 5 mL of bupivacaine) as a reproducible method to prolong peripheral blocks from approximately 6 to 8 hours to 10 to 12 hours without clinically relevant bradycardia or hypotension. He explained that dexmedetomidine’s α₂-agonist properties synergize with sodium-channel blockade while inducing localized vasoconstriction, slowing vascular absorption. Barletta noted that “using these teeny, tiny volumes will still increase the duration of your block, but it does not cause any systemic effect,” implying that microdoses suffice to achieve meaningful extension without sedation or cardiovascular compromise. Ward advised labeling any batch-mixed vials (eg, a 50-mL bottle of bupivacaine plus 50 µg dexmedetomidine) and storing them according to the preservative’s expiration date to streamline workflow and ensure consistency.

Adding morphine to epidural bupivacaine

In the context of neuraxial blocks, Barletta described a standard epidural mixture consisting of bupivacaine (0.5 mg/kg) combined with morphine (0.05 mg/kg). This combination reliably doubles epidural analgesia, he said, extending effects from approximately 6 to 12 hours with bupivacaine alone to 12 to 24 hours when morphine is included. Barletta noted, however, that clinicians must account for morphine‐induced urinary retention, so he would not use this strategy in patients undergoing bladder surgery.

Buprenorphine for peripheral blocks

Ward and Barletta also addressed buprenorphine as an adjunct for peripheral nerve and tissue infiltration blocks, noting that it’s important to pay close attention to managing the administration volume. They cited studies whose results showed that adding buprenorphine at 0.005 to 0.01 mg/kg to local anesthetics can double the block duration.

They explained that given buprenorphine's standard concentration of 0.3 mg/mL, achieving a target dose of 0.005 to 0.01 mg/kg as an additive to local anesthetics can sometimes require a larger volume than ideal for certain blocks. Their recommended strategy involves preparing a consistent mixture of buprenorphine and local anesthetic, and then tailoring the injected volume of this prepared mixture to the specific anatomical site. For example, if 0.4 mL of buprenorphine solution (providing 0.12 mg of buprenorphine) is mixed with 1 mL of local anesthetic, the total volume prepared is 1.4 mL. However, for a site with limited capacity, such as a maxillary dental block, the clinician might opt to administer only half of this prepared mixture. This technique allows for better control of the final injected volume while maintaining the intended proportion of buprenorphine to local anesthetic, they said.

Clinical implications and recommendations

The speakers said that integrating these adjuvants into multimodal analgesia protocols can result in lower systemic opioid administration, reduced inhalant requirements, and improved postoperative comfort. The incremental cost is minimal, and the patient benefits can be substantial, they said.

Reference

Barletta M, McNerney T, Ward K. Top 7 local blocks for everyday practice. Presented at: Fetch dvm360 conference; May 31, 2025; Nashville, Tennessee.