In vitro pharmacological interaction of caffeine and first-line antibiotics is antagonistic against clinically important bacterial pathogens

Abstract

The in vitro antibacterial and interaction of pure caffeine powder with first line antibiotic against bacterial isolates was investigated by macrobroth dilution and the checkerboard assay methods. This study showed that caffeine and the antibiotics exhibited varied degree of antibacterial activities. While caffeine had MICs ranging between 67.19 and 268.75 µg/ml, chloramphenicol had MICs of between 0.98 and 31.25 µg/ml, kanamycin (15.63 – 62.5 µg/ml), nalidixic acid (0.49 – 250 µg/ml), erythromycin (0.49 – 62.5 µg/ml), tetracycline (1.99 to 62.5 µg/ml) and metronidazole (15.63 to 31.25 µg/ml). Combining ½ MICs and MICs of caffeine with the antibiotics as well as direct combination of caffeine and the antibiotics resulted in significant reduction of the effectiveness of the antibiotics. The fractional inhibitory concentration index (FICI) of the combination of ½ MICs of caffeine with the different antibiotics showed antagonistic interactions with the antibiotics except kanamycin having additive and indifferent interactions with caffeine. The (FICI) of the MICs of caffeine combined with antibiotics showed a reduction in the number of antagonistic interactions as chloramphenicol, nalidixic acid and erythromycin showed some indifferent interactions while kanamycin showed indifferent interaction alone. The direct combination of caffeine and the antibiotics resulted in significant antagonistic interactions higher than when caffeine, at the ½ MICs and MICs, was combined with the antibiotics. Although caffeine demonstrated significant antibacterial activity against the selected bacterial isolates, its combination with the selected antibiotics resulted in significant antagonistic interactions. Caffeine should not be combined with antibiotics as this could result in serious therapeutic failure and, possibly, drug toxicity in vivo.