Aminoglycoside dosing (gentamicin, tobramycin, amikacin)

Extended-interval and traditional dosing, and adjustment from levels, with a live drug-level curve.

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Inputs

Drug
Method

Patient Shared with every calculator

SexUsed by the equation
Actual (total) body weight
Enter, or fill the patient
mL/min

Open the CrCl calculator

How this dose was built

  1. Pick the right weight

    Aminoglycosides stay mostly in water, not fat. Use ideal weight, or adjusted weight if the patient is more than 20% above ideal.

  2. Kidneys clear the drug

    Elimination speed (k) depends on kidney function. Slower kidneys need longer gaps between doses.

  3. High peak kills bacteria

    Aminoglycosides kill harder at higher peaks, and keep working after levels fall (post-antibiotic effect).

  4. Low trough protects kidneys and ears

    Time with almost no drug lets the kidneys and inner ear recover. That is why extended-interval dosing works.

When to use
  • Gram-negative infections and synergy regimens requiring aminoglycosides.
Pearls and pitfalls
  • Extended interval is not well studied in pregnancy, burns over 20%, ascites, dialysis, or CrCl below 20 mL/min.
  • Synergy dosing for endocarditis uses lower targets.
  • Check a level after the first extended-interval dose per your nomogram or protocol.
Method and formulas
k=0.00293×CrCl+0.014
V=0.25×DW
Dose=Cpk×k×V×tinf×(1−e−kτ)1−e−k×tinf
where
k
Elimination rate constant, h⁻¹
V
Volume of distribution, L
DW
Dosing weight, kg
Cpk
Target peak, mg/L
tinf
Infusion time, h
τ
Dosing interval, h
Evidence
  1. Primary Nicolau DP, Freeman CD, Belliveau PP, et al. Experience with a once-daily aminoglycoside program administered to 2,184 adult patients. Antimicrob Agents Chemother. 1995;39(3):650-655.
  2. Primary Sarubbi FA Jr, Hull JH. Amikacin serum concentrations: prediction of levels and dosage guidelines. Ann Intern Med. 1978;89(5 Pt 1):612-618.
  3. Primary Sawchuk RJ, Zaske DE. Pharmacokinetics of dosing regimens which utilize multiple intravenous infusions: gentamicin in burn patients. J Pharmacokinet Biopharm. 1976;4(2):183-195.