Studies on the existence of synergism between different antibiotics and a phenothiazine tranquilizer, promazine, possessing antimicrobial property.

Different antibiotics were tested for their capacity to exhibit synergism when used in combination with promazine (Pr), a tranquilizer endowed with powerful antimicrobial property. For this purpose the minimum inhibitory concentration (MIC) of different antibiotics and Pr was first determined by spot inoculation technique on nutrient agar plates to select the concentrations of the antibiotics and Pr to be used as well as the sensitive strains. It was observed that Pr in combination with tetracycline (Tc) demonstrated a marked enhancement of the inhibitory capacity of each drug, both against the Gram-positive and Gram-negative bacteria, following disc diffusion technique. The in vitro findings were further substantiated with the in vivo effects of Pr along with Tc using Salmonella typhimurium NCTC 74 as the challenge strain in mice. The synergism obtained was further corroborated in terms of the increase in the size of their inhibition zones compared with their unaltered individual zones to determine the level of significance. This result was also confirmed by the checkerboard test using doubling dilutions of both the agents.