Poly(DL:lactic acid-castor oil) 3:7-bupivacaine formulation: Reducing burst effect prolongs efficacy in vivo

Marina Sokolsky-Papkov*, Ludmila Golovanevski, Abraham J. Domb, Carolyn F. Weiniger

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

15 Scopus citations


Prolonged analgesia may be achieved using a single injection of slow-release local anesthetic formulation. The study objective was to improve the efficacy of a previously reported formulation comprising 10% bupivacaine in poly(DL:lactic acid co castor oil) 3:7. The polymer was loaded with 15% bupivacaine and injected through a 22G needle close to the sciatic nerve of ICR mice. Sensory and motor nerve blockade were measured. The efficacy and toxicity of the polymer-drug combination were determined. Sixty percent of the incorporated bupivacaine was released during 1 week in vitro. During in vitro release no burst effect was seen, suggesting low toxicity of the formulation. Single injection of 0.1 mL of 15% polymer-bupivacaine formulation caused motor block that lasted 64 h and sensory block that lasted 96 h. The MTD of the polymer-drug formulation was established as 0.175 mL. Microscopic examination of the injection sites revealed reversible nerve inflammation and normal internal organs. The polymer poly(DL:lactic acid co castor oil) 3:7 is a safe carrier for prolonged activity of bupivacaine up to 96 h. The increase of drug load in the formulation reduces the drug release rates due to stronger polymer-drug interactions and higher overall hydrophobicity of the formulation.

Original languageEnglish
Pages (from-to)2732-2738
Number of pages7
JournalJournal of Pharmaceutical Sciences
Issue number6
StatePublished - Jun 2010
Externally publishedYes


  • Biocompatibility
  • Biodegradable polymers
  • Injectables
  • Polymeric carrier
  • Polymeric drug delivery systems


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