In view of the large number of incompatibilities among drugs, the possibility was examined that lidocaine hydrochloride, 2 gm/100 ml, might inactivate antibiotics with which it was mixed for local injection. Incubation of this anesthetic with each of seven antimicrobial agents resulted in no loss of antibacterial activity when measured by agar-diffusion bioassay.
Barza M, Ernst C, Baum J, Weinstein L. Effect of Lidocaine on the Antibacterial Activity of Seven Antibiotics. Arch Ophthalmol. 1974;92(6):514–515. doi:10.1001/archopht.1974.01010010528014