Tobramycin

C. diff Risk

Low

Oral Bioavailability

NA

Approximate Cost

Spectrum Of Activity

General Information

Common Usage

It is recommended to use Extended Interval Dosing if possible for optimal bactericidal activity, convenience, potentially reduced risk of nephrotoxicity and reduced cost for administration.

Extended interval aminoglycoside dosing is the preferred dosing regimen but should NOT TO BE USED in the following:

  • Burns >20% TBSA (total burn surface area)

  • Ascites

  • Pregnancy

  • Renal impairment (creatinine clearance < 40 mL/min)

If excluded, refer to Conventional Dosing.

Drug Monitoring

Serum Drug Concentrations
Conventional Dosing:
Desired trough level: < 2 mg/L
Desired peak level: 4 to 10 mg/L

  • Consult Pharmacist for monitoring and dose adjustments

  • Desired trough concentration (taken prior to the 3rd dose)

  • Desired peak concentration (taken 30 minutes after the complete infusion of the 3rd dose)

  • Lower concentrations may be adequate for less severe infections (i.e. UTI)

Extended Interval Dosing:
Desired trough level: < 0.5 mg/L

  • Consult Pharmacist for monitoring and dose adjustments

  • 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

Follow-up Monitoring
If therapy is to be continued for greater than 7 days then:

  • 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

Adverse Effects

Nephrotoxicity (non-oliguric)

Vestibulocochlear toxicity

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

Major Interactions

Avoid concurrent nephrotoxic or ototoxic drugs (e.g. furosemide) whenever possible

Additional Information

Recommended Calculations

Body weight calculation (kg)
ABW = actual body weight
IBW = ideal body weight

  • IBW (male) = 50.0 kg + [2.3 kg x (each inch greater 5 feet)]

  • IBW (female) = 45.5 kg + [2.3 kg x (each inch greater 5 feet)

DBW = dosing body weight

  • DBW = 0.4 x (ABW – IBW) + IBW

For “non-obese” patients use: ABW
For “obese” patients use: DBW

  • Consider “obese” if (ABW - IBW) / IBW is greater than 0.2

Creatinine clearance (mL/min)
CrCl (male) = [(140 – age) x weight x 60] / [50 x serum creatinine (umol/L)]

CrCl (female) = CrCl (male) x 0.85

Age is in years.

Weight (kg) = ABW if non-obese, or = DBW if obese

Pharmacology

Antimicrobial class: Aminoglycoside

Pregnancy category: D