In vitro antibacterial activity of some antihistaminics belonging to different groups against multi-drug resistant clinical isolates

Abstract

Antihistaminics are widely used for various indications during microbial infection. Hence, this paper investigates the antimicrobial activities of 10 antihistaminics belonging to both old and new generations using multiresistant Gram-positive and Gram-negative clinical isolates. The bacteriostatic activity of antihistaminics was investigated by determining their MIC both by broth and agar dilution techniques against 29 bacterial strains. Azelastine, cyproheptadine, mequitazine and promethazine were the most active among the tested drugs. Diphenhydramine and cetirizine possessed weaker activity whereas doxylamine, fexofenadine and loratadine were inactive even at the highest tested concentration (1 mg/ml). The MIC of meclozine could not be determined as it precipitated with the used culture media. The MBC values of antihistaminics were almost identical to the corresponding MIC values. The bactericidal activity of antihistaminics was also studied by the viable count technique in sterile saline solution. Evident killing effects were exerted by mequitazine, meclozine, azelastine and cyproheptadine. Moreover, the dynamics of bactericidal activity of azelastine were studied by the viable count technique in nutrient broth. This activity was found to be concentration-dependant. This effect was reduced on increasing the inoculum size while it was increased on raising the pH. The post-antimicrobial effect of 100 g/ml azelastine was also determined and reached up to 3.36 h.

Reversal of antibiotic resistance in Gram‐positive bacteria by the antihistaminic azelastine

“…The number of survivors was further reduced by extra 2-4 log cfu ⁄ mL at pH 7 and 8 compared with the bacterial counts at pH 5 of the cultures treated with the same azelastine-antibiotic combinations. This seems to be due to the effect of pH on the antibacterial activity of azelastine, probably as a result of the pH of the medium on the surface activity and aggregation properties of azelastine, which would affect its influence on bacterial membrane permeability (5). This is of clinical interest in case of the systemic administration where the physiological pH is 7.4.…”

“…Azelastine is a phthalazinone non-sedating new generation antihistaminic drug widely used in the management of allergic conditions. Azelastine possesses certain antibacterial activity against a variety of microorganisms (5) due to its ability to induce alterations in membrane permeability and disruption of its integrity as previously shown (6). However, its interaction with antibiotics was not reported in the literature.…”

Antimicrobial Properties on Non-Antibiotic Drugs in the Era of Increased Bacterial Resistance

“…Azelastine has proven a great ability to provide bactericidal activity on the following Gram-positive bacteria: Staphylococcus aureus and Staphylococcus epidermidis, Enterococcus faecium [35]. While the antihistamine hasa moderate effect on Escherichia coli and Klebsiella spp., there are no results on Ps.…”

“…While the antihistamine hasa moderate effect on Escherichia coli and Klebsiella spp., there are no results on Ps. Aeruginosa [35]. The post-antimicrobial effect of azelastine was studied against Staphylococcus aureus and E. coli isolates [35].…”

“…Aeruginosa [35]. The post-antimicrobial effect of azelastine was studied against Staphylococcus aureus and E. coli isolates [35]. The post-exposure effect was sustained for 3.36 h against the tested Staphylococcus aureus isolate compared to only half an hour for the Escherichia coli isolate [35].…”