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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.

GENTAMICIN

Indication

  • the treatment of suspected or documented bacterial infections, normally caused by Gram-negative organisms. The combination of gentamicin - ampicillin provides good initial coverage for most cases of suspected neonatal sepsis in the first week of life.

Pharmacology

  • gentamicin is an aminoglycoside antibiotic
  • aminoglycosides, which are generally bactericidal, are believed to act by irreversibly binding to 30S ribosomal subunits, thereby inhibiting protein synthesis
  • aminoglycosides are active against many aerobic Gram-negative bacteria and some Gram-positive bacteria; their clinical application is usually reserved for Gram-negative organisms
  • aminoglycosides are inactive against fungi, viruses and most anaerobic bacteria
  • the average serum half life of gentamicin in neonates (< 1 week) varies between 3 and 12 hours; the half life is inversely correlated to birth weight and gestational age

Side Effects

  • 8th nerve damage, deafness, ataxia, vestibulitis
  • renal failure
  • these effects are somewhat dose related, ie. the higher the dose, the greater the potential for toxicity

Precautions

  • never inject into a closed space (eg. pleural space or peritoneal cavity) in the neonate because there have been some reported incidences of sudden respiratory arrest in association with the injection
  • gentamicin may cause renal damage; therefore, accurate in and outs should be done
  • levels should initially be monitored before and after the dose on the fourth day of therapy if antibiotic therapy is to continue
  • take peak values 30 minutes after the end of the 30 minute infusion (should be 6-10 mg/L )
  • take trough values immediately before the next dose (should be < 1.4 mg/L )

Drug Interactions

  • furosemide and ethacrynic acid - increase ototoxicity
  • ticarcillin inactivates gentamicin if mixed together in vitro
  • cephalosporins - increased nephrotoxicity
  • skeletal muscle relaxants (eg. vecuronium) - gentamicin may potentiate muscle relaxation
  • vancomycin - concurrent use increases the risk of nephro and ototoxicity. Although it is generally not recommended, if this combination is used, then monitor serum levels of both drugs and renal function closely

Dose

  1. The following guidelines are for the FIRST WEEK OF LIFE.

    GESTATIONAL AGE

    > 35 weeks
    < 35 weeks

    DOSE AND FREQUENCY

    3.5 mg/kg q24h
    3 mg/kg q24h

    • pre and post levels with4th dose
    • given IV by slow infusion
  2. AFTER THE FIRST WEEK OF LIFE, a larger dose (3.5 mg/kg) with the frequency based on postconceptional age, may be appropriate.

    POST CONCEPTIONAL AGE

    < 26 weeks
    27-32 weeks
    > 32 weeks

    FREQUENCY

    q24h
    q18h
    q12h

Supplied

  • 5 mg/mL, wardstock vial prepared by pharmacy; stored in main medication fridge
  • 5 mg/mL patient specific syringe, prepared by Pharmacy

Reference

  1. McEvoy G K (ed): AHFS Drug Information, American Society of Hospital Pharmacists, 1991.
  2. Roberts, RJ: Drug Therapy in Infants, W.B. Saunders, Toronto, 1984.
  3. Watterberg KL, Kelly HW, Angelus P and Backstrom C: The need for a loading dose of gentamicin in neonates, Ther Drug Monitor 1989; 11:16-20.
  4. Bloome MR, Warren AJ, Ringer L and Walker PC: Evaluation of an empirical dosing schedule for gentamicin in neonates, Drug Intelligence and Clinical Pharmacy 1988; 22: 618-622.
  5. Taketomo CK, Hodding JH and Kraus DM: Pediatric Dosage Handbook, Lexi-Comp Inc., Cleveland, 1992.



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