Antimicrobials
Tobramycin

Tobramycin

Low
N/A

Dosing

General Information

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

Pregnancy: 

  • Tobramycin crosses the placenta.
  • No reports linking the use of tobramycin to congenital defects have been located.
  • Ototoxicity, which is known to occur after tobramycin therapy in humans, has not been reported as an effect of in utero exposure. 
  • However, other aminoglycosides (streptomycin) have been associated with infant ototoxicity following in utero exposure. If tobramycin is required to treat a serious maternal infection, benefit likely outweighs potential risk.

Breastfeeding: 

  • Only very small amounts of tobramycin are found in breast milk and tobramycin is poorly orally absorbed.
  • Likely compatible.
  • Monitor infant for gastrointestinal side effects.
  • Maternal use of an ear drop or eye drop that contains tobramycin presents little or no risk for the nursing infant.

Extended interval dosing:

  • Consult Pharmacist for monitoring and dose adjustments
  • Desired trough level: < 0.5 mg/L
  • May consider drawing a trough concentration after the 1st dose to assess for potential drug accumulation, or drawing a trough concentration if there are concerns with renal function

Conventional dosing:

  • Consult Pharmacist for monitoring and dose adjustments
  • Trough target: < 2 mg/L, to be taken prior to the 3rd dose
  • Peak target: 4-10 mg/L, to be taken 30 minutes after the complete infusion of the 3rd dose
    • Lower concentrations may be adequate for less severe infections (i.e. UTI)

If therapy to be continued for greater than 7 days:

  • Twice weekly serum creatinine and BUN to assess for changes in renal function and risk for nephrotoxicity
  • A rise in serum creatinine of 25% from baseline requires reassessment of continued aminoglycoside use
  • Weekly serum trough concentrations to assess for drug accumulation and risk for nephrotoxicity
  • Close monitoring for ototoxicity is required
    • Onset of auditory and vestibular symptoms cannot be readily predicted and may be irreversible once they occur
    • Consider baseline and ongoing audiometric/vestibular testing in patients who are anticipated to have a prolonged duration of therapy (> 14 days) if possible
    • If unable to perform testing for ototoxicity, assess regularly for symptoms related to changes in cochlear (e.g. tinnitus, sense of fullness in ears, loss of hearing) and vestibular (e.g. dysequilibrium, oscillopsia, cognitive dysfunction, visual sensitivity, nausea/vomiting, vertigo, headache, nystagmus) function
  • Avoid concurrent nephrotoxic or ototoxic drugs (e.g. furosemide) whenever possible

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

Vestibulocochlear toxicity (irreversible)- require audiology testing if prolonged use

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

Increased nephrotoxicity with: amphotericin B, cyclosporine, cisplatin, NSAIDS, contrast dye, vancomycin.

Increased ototoxicity: furosemide.

Neuromuscular blockade agents- respiratory paralysis.

Inform patient of risk of ototoxicity to report any symptoms

Contraindicated in patients with myasthenia gravis

Antimicrobial class: Aminoglycoside

Average serum half life: 3.0

Biliary penetration: Moderate

CSF penetration: Poor

Lung penetration: Therapeutic

Urine penetration: Therapeutic