Gentamicin

Restricted
Restricted

C. diff Risk

Low

Oral Bioavailability

NA

Approximate Cost

Dosing

Adult

Once Daily/Extended Interval Dosing
7mg/kg dosing body weight (DBW) IV q24h

Multiple Daily Dosing
1.5-2mg/kg dosing body weight (DBW) loading dose then 1.5 mg/kg DBW IV q8h

Gram positive - synergy dosing
1mg/kg/dose dosing body weight (DBW) IV q8h

DBW = Dosing body weight - see Additional information

General Information

Common Usage

Empiric (in combination) or targeted therapy for suspected or confirmed Gram negative infections.

Empiric therapy for pyelonephritis.

Used synergistically in Gram positive infections (e.g Enterococcus spp. endocarditis)

Drug Monitoring

Monitor serum creatinine, BUN 2-3 times/week. Discontinue if any signs of ototoxicity.

For once daily/extended interval dosing dosing:

  • Peak levels are not recommended

  • NO level is required in patients with good renal function and therapy anticipated to be less than 8 days

  • Patient populations to consider a serum concentration independent of duration of therapy:

    • critically ill patients
    • rapidly changing renal status
    • increased or rapidly changing Vd (e.g. ascities, burn)
    • serum Cr unreliable indicator of renal function
    • concurrent nephrotoxic therapy (amphotericin B, vancomycin, chemotherapy, high furosemide, cyclosporine or tacrolimus etc.)

A single serum concentration can be drawn between 6 to 14 hours after the start of the aminoglycoside infusion (typically a 8-10 hour post concentration is drawn.)

  • Contact pharmacy for monitoring set up, level interpretation and dose individualization.

For conventional multiple times per day dosing:

  • Target Peak 3-10 mg/L, Trough <2 mg/L. Peak levels usually not required but if drawn, record time of dose and time of level draw as accurately as possible.

  • Contact pharmacy for monitoring set up, level interpretation and dose individualization

NB: Trough level is 30-60min BEFORE next dose dose, and peak is 30-60min AFTER dose infused.

For Gram-positive synergy dosing:

  • Target Peak 3-5 mg/L, Trough <1 mg/L. Peak levels usually not required but if drawn, record time of dose and time of level draw as accurately as possible.

  • Contact pharmacy for monitoring set up, level interpretation and dose individualization

For Intermittent OR Continuous dialysis:

  • Contact pharmacy for monitoring set up, level interpretation and dose individualization

Adverse Effects

Nephrotoxicity (non-oliguric)

  •  Avoid concomitant nephrotoxins

  •  Less common with once daily dosing

  •  Greater toxicity with longer duration and supratherapeutic trough levels

Vestibulocochlear toxicity

  • Irreversible

  • Require audiology testing if prolonged use

Can exacerbate neuromuscular blockade

  •  Contraindicated in patients with myasthenia gravis

Major Interactions

Increased nephrotoxicity

  •  Amphotericin

  •  Vancomycin

  •  Cyclosporin

  •  NSAIDs

  •  Contrast

Increased ototoxicity

  •  Loop diuretics (e.g. furosemide)

Non-depolarizing muscle relaxants may be potentiated

Additional Information

  • Perform baseline and ongoing weekly otovestibular toxicity assessment. Formal audiology assessment required if symptoms develop.

  • Inform patient of risk of ototoxicity and to report any symptoms.

Calculation of Dosing Body Weight (DBW)
DBW = IBW + [(ABW - IBW) x 0.4]

where:
IBW male = 50kg + 0.906kg [Height (cm) - 152.4cm]
IBW female = 45kg + 0.906kg [Height (cm) - 152.4cm]

Dosing Body Weight = DBW
Ideal Body Weight = IBW
Actual Body Weight = ABW

Pharmacology

Antimicrobial class: Aminoglycoside

Pregnancy category: D

Average serum half life: 2 hours

Biliary penetration: Moderate

CSF penetration: Poor

Lung penetration: Therapeutic

Urine penetration: Therapeutic