Gentamicin

C. diff Risk

Low

Oral Bioavailability

NA

Approximate Cost

$10-30/d

Dosing

Renally cleared, requires dosage adjustment with changes in renal function. Consult a pharmacist for renal dosing.

General Information

Drug Monitoring

Monitor creatinine at least weekly and more often if levels are elevated or other signs of renal dysfunction arise. Discontinue if any signs of ototoxicity (tinnitus, fullness in ears, dizziness).

Serum Level Monitoring for EXTENDED Interval Dosing, pediatrics: For most patients and indications, no levels are necessary, unless: Patients suspected at high risk for development of nephrotoxicity or renal dysfunction, or duration of treatment more than 5 days. In these cases check trough level prior to any dose to ensure that it is less than 1 mg/L. In cases where there is concern regarding treatment efficacy due to lack of response or severe infection treated with monotherapy, for cystic fibrosis (CF) or febrile neutropenia: Draw TWO levels, one 2 to 3 hours and one 6 to 8 hours after first dose. Refer to Calgary Zone Once Daily Aminoglycoside Calculator (in monograph) to calculate target parameters

Serum Level Monitoring for EXTENDED Interval Dosing, neonates: If plan is to discontinue gentamicin pending 48-hour culture results, no levels are required unless indicated for renal dysfunction. If plan is to continue antibiotics beyond 48 h culture results draw a 22 hour level on all neonates regardless of ordered dosing interval.

  • If 22 h level is: 1.2 mcg/mL or less- give every 24h.

  • 1.3 to 2.6 mcg/mL- give every 36h

  • 2.7 to 3.5 mcg/mL- give every 48h

  • 3.6 mcg/mL or more- Hold next dose, repeat level in 24 hours. Base interval on time to reach trough level less than 2 mcg/mL. Repeat 22h level if therapy continues beyond 7 days.

Serum Level Monitoring for CONVENTIONAL Dosing: Obtain drug levels with the third or fourth dose. Peak serum levels are drawn 30 minutes after the end of an IV infusion or one hour post-IM injection. Peak levels are: 5 to 10 mcg/mL and 12 to 15 mcg/mL in cystic fibrosis. Trough levels are drawn just prior to the next dose and should be less than 2 mcg/mL.

Serum Level Monitoring for Synergistic Dosing: Levels are typically not required. If done, targets are: Peak 3 to 5 mg/L and trough less than 2 mg/L.

Major Interactions

Enhanced nephrotoxic effect with concomitant use of other nephrotoxins

Enhanced ototoxicity with loop diuretics (e.g. furosemide).

Non-depolarizing muscle relaxants may be potentiated.

Pharmacology

Antimicrobial class: Aminoglycoside

Average serum half life: - Neonates: 3-11.5 hours

  • Infants: 4 ± 1 hour

  • Children: 2 ± 1 hour

  • Adolescents:1.5 ± 1 hour

  • Adolescents: 1.5 ± 1 hour

  • Adults: 1.5- 3 hours; End stage renal disease: 30-70 hours

Route of Elimination: Almost completely by glomerular filtration of unchanged drug with excretion into urine.