Lidocaine and bupivacaine syringe stability study

Introduction:

Mixtures of lidocaine with bupivacaine are used for sensory blockade to control pain at the time of a procedure and to decrease discomfort. Combining the two anesthetic agents in one syringe offers an advantage of the rapid onset of lidocaine and the prolonged duration of bupivacaine. 

Objectives:

The purpose of this study was to test the stability of a mixture yielding 1% lidocaine and 0.25% bupivacaine in a 5 mL BD syringe at room temperature without protection from light over the course of nine days.

Study Design:

This was a compatibility and stability study of lidocaine and bupivacaine mixture. 

Methods:

We used the previously established HPLC method using an Agilent SB-C18 3.5 µm 4.6x250 mm column with a mobile phase of 30 mM potassium dihydrogen phosphate buffer (0.16% triethylamine, pH adjusted to 4.85) and acetonitrile in a ratio of 63:37 (v/v) with UV detection at 220 nm. Peak areas were used to determine the concentration of a compound in the sample.  A mixture of 1% lidocaine and 0.25% preservative-free bupivacaine was prepared and used to fill three 5 mL BD syringes. The samples were kept at room temperature and were not protected from light. The treatment with acid, base, oxidation, and heat provided insight into degradation pathways and products. 

Results:

Calibration curves were constructed for each analyte over the concentration range of 5-15 mg/mL of lidocaine and 1.5-3.5 mg/mL of bupivacaine. A regression analysis for each standard yielded an R² ≥0.995. The retention times for lidocaine and bupivacaine were 4.6 and 7.2 minutes, respectively. The graph of concentration of each analyte as a function of time showed no degradation over the period of nine days.  

Conclusions:

This study showed that solution of lidocaine 2% and bupivacaine 0.5% will be stable when stored in a BD syringe at room temperature without protection from light for nine days.