Dose:    75 mg/kg/dose IV, IM

Frequency: Q 12 hours if < 1 week of age
                     Q    8 hours if > 1 week of  age
                      See comments if VLBW or > 1 month of age            
                      Adjustments for hepatic or renal failure.

Comments: Mezlocillin is a ureidopenicillin and should be considered a second-line antibiotic. It is effective in the treatment of gram negative bacteria, especially in the treatment of Pseudomonas infections. Though it has a wide spectrum of activity, it does not have greater intrinsic activity than penicillin g against penicillin-susceptible organisms. Mezlocillin is also active against beta-lactamase positive and negative H. influenza though there is no specific indication to use the drug for this purpose. Mezlocillin should not be used alone in the treatment of Pseudomonas infections (Eliopoulous and Moellering. An Int Med 1982; 97:755). When used with gentamicin, a modest in vitro synergism has been noted; however, the main reason for using an aminoglycoside is to prevent the development of bacterial resistance during treatment. Unfortunately, this combined therapy negates its minimal nephrotoxicity. Therapeutic concentrations are reached in most tissues and fluids.

    Aminoglycosides are inactivated by mezlocillin; therefore, the drugs should be given separately. The interaction becomes clinically significant if assays for aminoglycoside levels in serum are delayed, a falsely lowered level may result. In neonates, the dose is 75 mg/kg given every 12 hours if less than one week of age, and every 8 hours if one week to one month of age. The dosage interval for infants one to six months of age is 50 mg/kg given every 4 to 6 hours. The appropriate dose and intervals for VLBW infants are not well established though recent work demonstrates that clearance of the drug increases with gestational age and postnatal age (Jungbluth, Dev Pharmacol Ther 1988; 11:317).

Toxicity:  Adverse reactions occur infrequently and tend to be minor. These reactions include maculopapular rashes (similar to "ampicillin rashes"), eosinophilia, and leukopenia which improve after discontinuing the drug. See adverse reactions associated with penicillin .

Preparation: Mezlocillin (Mezlin) is available in a 1 gram vial.  Add 10 ml of sterile water for injection to the vial to obtain a 100 mg/ml concentration.  Refrigerate, stable for 24 hours after vial entered.   Infuse over 3 to 5 minutes.  For IM administration, each gram of mezlocillin should be reconstituted using 3 to 4 ml of sterile water for injection.

Compatibility: Compatible with TPN if given by "Y-site" infusion but no information available about filter.  Compatible with D5W, D10W, sterile water for injection, and normal saline.  It is also compatible with aztreonam, famotidine, heparin, morphine, and propofol.    Mezlocillin is incompatible with amiodarone, any aminoglycoside (amikacin, gentamicin, and tobramycin are most likely to be used in the NICU), and filgrastim.