What body weight is used for aminoglycoside dosing?

For patients at or below ideal body weight (IBW), actual body weight (ABW) is used. For obese patients (ABW > 1.3 × IBW), a dosing weight (DW) is calculated as IBW + 0.4 × (ABW − IBW). This calculator auto-selects the appropriate weight and displays which one was used.

What is extended-interval dosing?

Extended-interval (or once-daily) aminoglycoside dosing gives a larger single dose — typically 5–7 mg/kg for gentamicin/tobramycin or 15 mg/kg for amikacin — once every 24, 36, or 48 hours depending on renal function. This exploits the concentration-dependent killing and post-antibiotic effect of aminoglycosides while minimizing nephrotoxicity during the drug-free trough period.

How is creatinine clearance estimated?

CrCl is estimated with the Cockcroft-Gault equation: CrCl = [(140 − age) × weight × (0.85 if female)] / (72 × SCr). Weight used is the actual or dosing weight as selected. For patients with SCr below 0.6 mg/dL, a floor of 0.6 is applied to avoid overestimating CrCl.

Why are aminoglycosides dosed differently from other antibiotics?

Aminoglycosides exhibit concentration-dependent bactericidal activity and a prolonged post-antibiotic effect. Higher peak concentrations relative to the MIC improve killing. Nephrotoxicity is linked to sustained drug levels in renal tubular cells, so a drug-free interval (low trough) reduces toxicity. These properties favor large infrequent doses over small frequent ones.

When should extended-interval dosing NOT be used?

Extended-interval dosing is generally avoided in pregnancy, burns covering > 20% BSA, ascites, endocarditis (especially enterococcal synergy dosing), and CrCl < 20 mL/min. Traditional dosing with pharmacokinetic monitoring is preferred in these populations. Always verify with institutional guidelines.

Is this calculator a replacement for therapeutic drug monitoring?

No. Aminoglycosides require serum level monitoring (peaks and troughs or Hartford 6–14 h levels) to individualize therapy. This tool provides initial dose estimates only. Dosing must be adjusted based on measured levels and clinical response by a licensed pharmacist or physician.

Aminoglycoside Dosing Calculator

Name: Aminoglycoside Dosing Calculator
Availability: InStock
Author: Nham Vu

Calculate weight-based initial doses and extended-interval (Hartford nomogram) dosing for gentamicin, tobramycin, and amikacin based on patient weight and renal function.

Patient Parameters

Age (years)

Sex

Height (cm)

Actual Weight (kg)

Serum Creatinine (mg/dL)

Aminoglycoside

Educational reference only. All dosing results must be verified by a licensed pharmacist or physician. This tool does not replace clinical judgment or therapeutic drug monitoring.

Enter patient data and click Calculate Dose

Summary

Calculate weight-based initial doses and extended-interval (Hartford nomogram) dosing for gentamicin, tobramycin, and amikacin based on patient weight and renal function.

How it works

Enter patient age, sex, actual body weight, and serum creatinine.
Select the aminoglycoside: gentamicin, tobramycin, or amikacin.
The tool calculates creatinine clearance using the Cockcroft-Gault equation.
Traditional dosing is shown: standard mg/kg dose divided into q8h, q12h, or q24h intervals adjusted for CrCl.
Extended-interval dosing is calculated using the Hartford nomogram target dose (7 mg/kg for gentamicin/tobramycin; 15 mg/kg for amikacin) with interval selected by CrCl.
Results display the calculated dose per interval, total daily dose, and the estimated dosing interval.

Use cases

Calculate an initial gentamicin dose for gram-negative bacteremia.
Determine tobramycin dosing for a patient with mild renal impairment.
Apply Hartford nomogram extended-interval amikacin for serious infections.
Estimate CrCl before selecting aminoglycoside dosing interval.
Support pharmacy students learning aminoglycoside pharmacokinetics.
Cross-check a clinical dose recommendation during rounds.
Compare traditional versus extended-interval strategies side by side.
Screen for dose adjustments needed in elderly or renally impaired patients.

Frequently Asked Questions

Last updated: 2026-07-01 · Reviewed by Nham Vu