Tobramycin

C. diff Risk

Low

Oral Bioavailability

NA

Approximate Cost

$12/day

Dosing

Renal

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

General Information

Common Usage

Pseudomonal and other gram negative infections, inhaled form used in cystic fibrosis

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:
Obtain trough concentrations when treatment is anticipated to be longer than 48 hours.
Measure trough level 1 hour prior to second dose.Target trough: less than 1 microgram/mL.If trough is less than 1 microgram/mL, continue current dose and repeat trough every 7 days. If indicated, may measure peak level with first dose 30 minutes following 30 minute IV infusion. Target peak: 15-25 micrograms/mL.

Serum Level Monitoring for EXTENDED Interval Dosing, Neonates:
Check tobramycin level at 22 hours post start of infusion, regardless of the dosing interval that the patient is started on for all patients with an anticipated tobramycin treatment greater than 48 hours.
For patients less than or equal to 7 days of age in whom anticipated tobramycin treatment duration is less than or equal to 48 hours (i.e. clinical suspicion for early-onset sepsis is low), only order 22 hour tobramycin level if any or the following criteria apply:

  • urine output less than 1 mL/kg/h or a serum creatinine greater than or equal to 120 umol/L

  • hypoxic ischemic encephalopathy

  • concurrent ibuprofen/indomethacin administration

  • concurrent furosemide, vancomycin, vasopressor, or inotrope administration

  • severe cardiac anomalies

  • less than or equal to 29 weeks gestation or less than 1500 grams birth weight

Adjust dosing interval based on the 22-hour level drawn with the first dose by referring to the information below or in discussion with the pharmacist.

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

  • 1.3 to 2.6 mcg/mL- give dose every 36h

  • 2.7 to 3.5 mcg/mL- give dose every 48h

  • 3.6 mcg/mL or more- Hold next dose, repeat level in 24 hours
    If levels are within target range continue current dosing regimen. Repeat 22 hour level every 7 days or sooner if clinically necessary. Peak levels are not routinely measured but may be ordered if severe gram negative infection or concern about clinical progress.

Serum Level Monitoring for EXTENDED Interval Dosing, Women's Health:
For anticipated duration of therapy more than 48 hours monitor serum tobramycin levels as follows.
Measure level 18 hours after start of infusion (based on 30 minute infusion) to assess for adequate clearance. Target 18 hour level: 1 microgram/mL or less.
If 18 hour level is within desired range, repeat every 4 days or sooner if clinically necessary.

Adverse Effects

  • Nephrotoxicity (non-oliguric)- less common with once daily dosing; greater toxicity with longer duration and supratherapeutic trough levels; avoid concomitant nephrotoxins

  • Vestibulocochlear toxicity (irreversible)- suggest audiology testing if prolonged use

  • Can exacerbate neuromuscular blockade- e.g. contraindicated in patients with myasthenia gravis.

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

Route of Elimination: With normal renal function, 93% of dose excreted in urine within 24 hours

Average serum half life: Neonates: ≤1200 g: 11 hours, >1,200 g: 2 to 9 hours.
Infants: 4 ± 1 hour.
Children: 2 ± 1 hour.
Adolescents: 1.5 ± 1 hour
Adults: IV: 1-2 hours; directly dependent upon glomerular filtration rate
Adults with impaired renal function: 5- 70 hours