A new powerful antibacterial synergistic combination of trimethoprim and trimeprazine

The antihistaminic phenothiazine trimeprazine (Tz) was found to exhibit significant antibacterial activity on the basis of in vitro and in vivo tests. For the study of synergism due to a combination between Tz and trimethoprim (Tm), drug soaked filter paper discs were placed on young culture lawns of sensitive bacteria on nutrient agar plates. Calculation of the area of inhibition zones for determining the degree of synergism between Tz and Tm showed the increase to be statistically significant (p<0.01) when compared with their individual effects. By the checkerboard assessment procedure, the fractional inhibitory concentration (FIC) index was found to be 0.18, confirming synergism. The protective capacity of this combination was then assessed in Swiss white mice using S. typhimurium as the challenge bacterium, and the level of bacterial load was determined from infected autopsied animals. Statistical analysis of the data by students 't' test finally proved that a combination of Tz+Tm was highly synergistic.