Studies on synergism between penicillins and ambodryl (bromodiphenhydramine HCl), an antihistamine with antimicrobial property.

With respect to 31 different selected test bacteria, all sensitive to benzyl penicillin (Pc), ampicillin (Ap), methicillin (Me), ceporan (Ce), cloxacillin (Cx), streptomycin (Sm), kanamycin (Km), gentamicin (Gm), chloramphenicol (Cm), tetracycline (Tc), polymyxin (Pm) as well as ambodryl [Am; an antihistamine (bromodiphenhydramine HCl) with distinct antimicrobial properties], it was found that Am in combination either with Pc, Ap, Ce or Me consistently showed enhancement of antimicrobial effects resulting from synergism. A combination of Am with either Sm, Km, Gm or Tc, on the other hand, showed only additive effects. An interaction of the activities of Am with Pm also resulted in indifference effects. Determination of the area of inhibition zone, calculated from its diameter for the degree of synergism in case of Am and Pc, showed these synergistic effects to be significant (P less than 0.05) in comparison with their individual effects: this was corroborated by the determination of the fractional inhibitory concentration (FIC) index which was found to be less than 0.5. The synergism of Am-Pc combination was confirmed by in vivo studies by challenging mice with a virulent strain of S. typhimurium and looking for protection.