Mezlocillin and related antibiotics

Chemical manipulations produce a seemingly endless series of beta-lactam antibiotic derivatives with highly specialized antimicrobial activities. A new class called the ureidopenicillins includes mezlocillin (Mezlin®, Miles Pharmaceuticals) and azlocillin. Mezlocillin has recently been approved by the Food and Drug Administration for clinical use in pediatric patients including newborns. Azlocillin is not yet approved for general use. Its major difference from mezlocillin is greater in vitro activity against Pseudomonas aeruginosa at the expense of somewhat lesser activity against Gram-neglative enteric organisms. Piperacillin (Pipracil®, Lederle Laboratories) is not a ureidopenicillin but its spectrum of activity is the same. Piperacillin has not been approved for use in infants and children. For the clinician, it is simplest to think of mezlocillin as a new ticarcillin or carbenicillin, the drugs which invite comparison because of range of activity and potency within the spectrum.