Disclaimer to the On-line Edition
This Manual has been designed for use in the NICU at London Health Sciences Centre (LHSC), London, Ontario, Canada, and represents clinical practice at this institution. The information contained within the Manual may not be applicable to other centres. If users of this Manual are not familiar with a drug, it is recommended that the official monograph be consulted before it is prescribed and administered. Any user of this information is advised that the contributors, Editor and LHSC are not responsible for any errors or omissions, and / or any consequences arising from the use of the information in this Manual.



  • imipenem/cilastatin is indicated for use in neonates at LHSC in the following instances:
    1. empiric therapy for seriously ill infants after standard therapy (aminoglycoside, ampicillin, ceftizoxime) has been considered and/or used.
    2. treatment of infections secondary to pathogens with documented resistance to first line antibiotics.


  • Primaxin(R) is an antibiotic with a broad in vitro antimicrobial spectrum. It consists of 2 components:
    1. imipenem, which is a carbapenem (a new class of beta-lactam), antibiotic, and
    2. cilastatin, an inhibitor of dehydropeptidase-1 (an enzyme located in the kidney that metabolizes and inactivates imipenem).
  • imipenem is bactericidal against aerobic and anaerobic Gram-positive and Gram-negative bacteria.
  • imipenem inhibits cell-wall synthesis by binding to penicillin-binding proteins.
  • in a study of 41 premature infants the elimination half life was 2.5h and 9.1h, for imipenem and cilastatin, respectively.(97) In this study renal clearance averaged 16% of total body clearance (comparative adult values for renal clearance have averaged approximately 50%).
  • Primaxin(R) is NOT active against Chlamydia spp, methicillin-resistant staphylococci S.epidermidis and S.aureus) or enterococci, among others. Because of the development of resistance, PrimaxinR should not be used alone to treat Pseudomonas aeruginosa infections.

Side Effects

  • local: phlebitis/thrombophlebitis, pain, induration (all < 2% incidence).
  • systemic:diarrhea, vomiting (< 2% incidence)
    : pseudomembranous colitis has been reported to occur in adults
  • CNS adverse reactions (eg. myoclonic activity, seizures) have been reported (in adults); this has occurred especially when recommended doses based on renal function have been exceeded and/or patients have a pre-existing CNS disorder (eg. brain lesion, history of seizures). IN CONSIDERATION OF THE ADULT EXPERIENCE, SPECIAL CONSIDERATION SHOULD BE GIVEN TO THE USE OF PRIMAXIN(R) IN INFANTS WITH POOR RENAL OR HEPATIC FUNCTION AND/OR PRE-EXISTING CNS DISEASE (eg. SEIZURES, IVH).


  • an imipenem dose of 20mg/kg q12h in infants < 36 weeks post conceptional age has been recommended. (It is suggested that the trade name be used when ordering this medication, ie, PrimaxinR _____mg IV Q12H).
  • administer via slow IV infusion (ie. over 30 minutes)


  • 5mg/mL (of both imipenem and cilastatin) syringe prepared by Pharmacy.
  • keep the syringes in the refrigerator.
  • if a vial (500 mg) of PRIMAXIN(R) is obtained when the Pharmacy is closed, it should be reconstituted as follows:
    1. Transfer approximately 10 mL from a 100 mL bag to the vial
    2. Shake the vial well
    3. Return the contents of vial to the remaining solution in the bag
    4. Repeat the above process using 10 mL of the diluted solution to ensure complete transfer of the contents of the vial to 100 mL bag solution
    5. There is now 500mg PRIMAXIN(R) in 100 mL of IV solution (this is equal to 5 mg/mL)


  1. Krogh CME et al (ed): Compendium of Pharmaceuticals and Specialties, Canadian Pharmaceutical Association, 1992.
  2. "Primaxin(R)", Product Information, Merck, Sharp and Dohme, Canada, 1987.
  3. Reed MD, Kliegman RM and Yamashita TS: Clinical pharmacology of imipenem and cilastatin in premature infants during the first week of life, Antimicrobial Agents and Chemotherapy 1990; 34: 1172-1177.
  4. Imipenem-cilastatin sodium (PrimaxinR), The Medical Letter, 1986 (March 14); 28: 29-30.

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