Antibacterial Activity of Ambodryl and Benadryl

Of nine antihistamines screened for in vitro antibacterial activity, ambodryl (bromodiphenhydramine hydrochloride) and benadryl (diphenhydramine hydrochloride) were the most active. At 50 to 100 μ/ml concentrations these inhibited a large number of Gram negative and Gram positive bacteria in vitro , with ambodryl having a broader spectrum. In vivo tests showed that the compounds at single doses of 3 and 1.5 μg/g body weight protected mice against a challenge with a virulent strain (LD₅₀) of Salmonella typhimurium , and also significantly reduced the multiplication of this organism in the liver, spleen and blood of the protected animals in comparison with the unprotected controls.