Larson and others studied the stability of lidocaine 2% with epinephrine 1:100 000 buffered by mixing 30 mL of this solution with 3 mL of 8.4% (1 mmol/mL) sodium bicarbonate under a sterile hood. The solution remained stable for 2 weeks when stored with refrigeration and for less than 1 week when stored at room temperature. Bartfield and others studied the chemical stability of plain buffered lidocaine solutions and found them to be stable for 7 days when stored at room temperature. However, both of these studies lacked proper validation of the methods and robust study design, which brings the validity of their results into question.
Several studies have evaluated clinical outcomes with buffered lidocaine. Bartfield and others performed concur­rent testing of the 1-week-old buffered lidocaine with 24 patients and found that it caused less pain during infiltration than lidocaine alone. Li and Brainard12 conducted a double- blind study comparing fresh and 2-month-old buffered lidocaine stored at room temperature. They found no difference between the 2 solutions in terms of analgesia; however, this method is not a true measure of chemical stability. A solution containing only 80% of the initial concentration may cause analgesia that is clinically indistinguishable from that produced by a freshly prepared solution, but it would not meet pharmaceutical standards.

Both epinephrine and lidocaine are more stable under acidic conditions and degrade under alkaline conditions. Under more aggressive alkaline conditions, the lidocaine amide moiety would be cleaved by the base, giving rise to 2,6-dimethylaniline. However, under mildly alkaline conditions only a minimal decrease in concentration would be expected. In this study, when the alkaline forced-degradation sample was heated for 9 days at 50°C, the concentration declined by only 19%. Oxidation of the lidocaine sample might lead to 2 new N-oxide products. Of the 2 active ingredients, epinephrine is more sensitive to these conditions and was therefore analyzed more frequently. The starting pH ranged from 7.45 to 7.8 and might not have been high enough to cause cleavage of the lidocaine molecule’s amide bond to create 2,6-dimethylaniline, but it would have been sufficient to accelerate degradation of the epinephrine. Epinephrine is also very sensitive to oxygen, and exposure to air during the compounding process would accelerate the degradation process; in contrast, lidocaine is more resistant to oxidation. Evidence of these 2 factors was seen in the results of accelerated degradation and was confirmed by the need to assign a shorter expiry date to the product containing epinephrine.
In conclusion, both 1% and 2% buffered lidocaine diluted (10:1) with 8.4% sodium bicarbonate were chemically stable for 28 days when packaged in polypropylene syringes and stored at 5°C with protection from light. Buffered lidocaine solutions containing epinephrine (1:100 000) remained stable for only 7 days when stored in polypropylene syringes at 5°C with protection from light. Because these expiry dates are based on physical compatibility and chemical stability only, institutions should assign their own expiry dates on the basis of results from sterility testing. levitra plus

These results are particularly important in facilitating the availability of buffered lidocaine for use when inserting IV lines, which will be helpful for younger children who require immediate placement of an IV line and for adults who require placement of a central IV line.