To investigate the in vitro effects of interactions between ciprofloxacin (CP) and magnesium-aluminium hydroxide (MA) combined against selected Gram-positive and Gramnegative bacteria. The interaction between CP and MA was accessed by agar diffusion method. Comparing the susceptibility of the isolates to CP alone with those of Ciprofloxacin-Magnesiumaluminum hydroxide (CPMA) combined showed that there were significant antagonistic and synergistic interactions in vitro. Antibacterial activities of ciprofloxacin were increased with 4.5-6.0 μg/ml of the MA but were drastically decreased with concentrations lower and higher than 4.5-6.0 μg/ml while development of resistant colonies within these zones of inhibitions was recorded. The susceptibility of the isolated resistant colonies was lesser than those obtained from the original isolates. The combination of ciprofloxacin (CP) and magnesium-aluminum hydroxide (Maalox) (MA) against bacterial isolates could result in development of resistant colonies. The roles of aluminum and magnesium in resistance development at the molecular level require further studies.