Buffered lidocaine hydrochloride solution with and without epinephrine: stability in polypropylene syringes

Pain associated with infiltrating the skin with lidocaine can be reduced by buffering the solution with sodium bicarbonate.

To determine the physical compatibility and chemical stability of lidocaine hydrochloride solution buffered with 8.4% sodium bicarbonate, with and without epinephrine, packaged in polypropylene syringes and stored at 5°C with protection from light.

Lidocaine solutions (1% and 2%), with and without epinephrine 1:100 000, were diluted 10:1 with 8.4% sodium bicarbonate, packaged in 3-mL polypropylene syringes, and stored at 5°C (range 3°C to 8°C). On each of days 0, 3, 7, 10, 14, 17, 21, 24, and 28, the contents of 3 syringes for each solution of lidocaine combined with epinephrine were collected separately in glass vials and frozen at -70°C for subsequent analysis. In addition, on days 0, 7, 14, 21, and 28, the contents of 3 syringes for each lidocaine solution without epinephrine were collected separately in glass vials and frozen at -70°C for subsequent analysis. Chemical stability was determined with a validated, stability-indicating high-performance liquid chromatography method. Changes in colour, clarity, and pH were used to determine physical compatibility of the solutions.

All buffered lidocaine solutions containing epinephrine (1:100 000) retained at least 93.3% of the original concentration of epinephrine and 97.5% of the lidocaine concentration for 7 days when stored at 5°C with protection from light. In contrast, the epinephrine-free solutions retained at least 94.7% of the initial concentration of lidocaine for the duration of the study (28 days). All samples remained clear, colourless, and free of precipitate throughout the study, and there were no significant changes in pH.

Extemporaneously prepared buffered lidocaine (1% and 2%) packaged in polypropylene syringes remained stable for up to 28 days when properly refrigerated with protection from light. A 7-day expiry date was established for buffered lidocaine solutions containing epinephrine, packaged in polypropylene syringes, and stored with refrigeration and protection from light.