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 Cockcroft-Gault using the selected weight in the numerator. This implementation uses actual body weight unless it exceeds 130% of IBW, then uses adjusted dosing weight: IBW + 0.4 × (ABW − IBW). It applies an SCr floor of 0.6 mg/dL. Weight selection, low-SCr handling, and extended-interval eligibility vary by protocol and must be verified locally.

When is extended-interval aminoglycoside dosing NOT appropriate?

Extended-interval dosing is generally avoided in pregnancy, burns >20% BSA, ascites, endocarditis (especially enterococcal synergy regimens), and severe or unstable renal dysfunction. Some institutional protocols also exclude morbid obesity. Traditional dosing with pharmacokinetic monitoring may be preferred; verify local eligibility criteria.

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

Enter patient data and an optional post-dose serum level to estimate an initial gentamicin/tobramycin interval using a simplified Hartford approach.

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, weight selection, renal-function assumptions, and extended-interval eligibility must be verified against the local protocol 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 patient data and an optional post-dose serum level to estimate an initial gentamicin/tobramycin interval using a simplified Hartford approach.

How it works

Enter patient age, sex, height, actual weight, and serum creatinine to estimate CrCl via Cockcroft-Gault using the displayed dosing-weight policy.
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: 2026-09-19 · Reviewed by Nham Vu

Aminoglycoside Dosing Interval Calculator

Patient Parameters

Post-Dose Level (Optional)

Recommended Dosing Interval

Renal Function Estimate

Suggested Starting Dose (7 mg/kg)

Post-Dose Level Evaluation

Summary

How it works

Use cases

Frequently Asked Questions

Aminoglycoside Dosing Interval Calculator

Use the Aminoglycoside Dosing Interval Calculator

Patient Parameters

Post-Dose Level (Optional)

Recommended Dosing Interval

Renal Function Estimate

Suggested Starting Dose (7 mg/kg)

Post-Dose Level Evaluation

Summary

How it works

Use cases

Frequently Asked Questions