What is the Hartford nomogram?

The Hartford nomogram is a method for extended-interval aminoglycoside dosing developed at Hartford Hospital. It uses a 7 mg/kg starting dose and selects the interval (q24h, q36h, or q48h) based on CrCl, then uses a 6–14 hour post-dose serum level plotted on the nomogram to confirm the interval is appropriate for the individual patient.

How is CrCl estimated?

Creatinine clearance is estimated with the Cockcroft-Gault equation: CrCl = [(140 − age) × weight × (0.85 if female)] / (72 × SCr). For patients with SCr below 0.6 mg/dL, a floor of 0.6 is applied to avoid overestimating CrCl. Weight used is the actual body weight unless the patient is obese, in which case dosing weight (IBW + 0.4 × (ABW − IBW)) is used.

When is extended-interval aminoglycoside dosing NOT appropriate?

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

What does the 6–14 hour post-dose level tell us?

A serum level drawn 6–14 hours after the first dose, when plotted on the Hartford nomogram, falls into one of three zones corresponding to q24h, q36h, or q48h. If the level falls in a longer interval zone than initially selected by CrCl alone, the interval should be extended. This step individualized the initial CrCl-based estimate.

Does this apply to amikacin?

The Hartford nomogram was originally designed for gentamicin and tobramycin (7 mg/kg target dose). Amikacin uses a 15 mg/kg target dose and its own nomogram with different level thresholds. This tool applies to gentamicin and tobramycin only.

Is this tool a replacement for therapeutic drug monitoring?

No. This tool provides initial interval selection only. Serum level monitoring and dose adjustment by a licensed pharmacist or physician are required during therapy.

Aminoglycoside Dosing Interval Calculator

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

Enter creatinine clearance and optional post-dose serum level to determine the recommended gentamicin/tobramycin dosing interval using the Hartford nomogram.

Patient Parameters

Age (years)

Sex

Height (cm)

Actual Weight (kg)

Serum Creatinine (mg/dL)

Drug

Post-Dose Level (Optional)

Hartford nomogram confirmation: draw level 6–14 h after the first dose.

Level (mg/L)

Hours post-dose

Educational reference only. All 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 Interval

Summary

Enter creatinine clearance and optional post-dose serum level to determine the recommended gentamicin/tobramycin dosing interval using the Hartford nomogram.

How it works

Enter patient age, sex, weight, and serum creatinine to estimate CrCl via Cockcroft-Gault.
The tool maps CrCl to the standard Hartford nomogram interval: ≥60 → q24h, 40–59 → q36h, 20–39 → q48h, <20 → not recommended.
Optionally, enter a 6–14 hour post-dose serum level drawn after the first dose.
The post-dose level is compared to the Hartford nomogram zone boundaries for the chosen interval to confirm suitability.
Results display the recommended interval, the Cockcroft-Gault CrCl, and any monitoring guidance.

Use cases

Select the starting q24h/q36h/q48h interval for a new extended-interval gentamicin order.
Confirm the dosing interval using the Hartford nomogram after drawing a 6–14h post-dose level.
Adjust gentamicin or tobramycin interval when renal function changes mid-course.
Educate pharmacy students on applying the Hartford nomogram in clinical practice.
Cross-check an interval recommendation before signing a pharmacokinetic consult.
Screen whether a patient with moderate renal impairment is a candidate for once-daily aminoglycoside therapy.

Frequently Asked Questions

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