Carbenicillin is a bacteriolytic antibiotic belonging to the carboxypenicillin subgroup of the penicillins. It has Gram-negative coverage which includes Pseudomonas aeruginosa but limited Gram-positive coverage. The carboxypenicillins are susceptible to degradation by beta-lactamase enzymes, although they are more resistant than ampicillin to degradation. Carbenicillin is also more stable at lower pH than ampicillin. Aqueous solutions are stable at room temperature for several hours and at +4°C up to 5 days. Prepare a stock solution with a concentration of 50 mg/ml in water and filter sterilize. Store the stock solution at -20°C. The working concentration varies from 20 - 100 µg/ml.