Hartford Nomogram Checker: Can This Gentamicin Level Be Used?
Hartford Nomogram Checker: Can This Gentamicin Level Be Used?
The Hartford nomogram turns one gentamicin or tobramycin level, 6 to 14 hours after a 7 mg/kg dose, into a q24h, q36h or q48h interval — but only for the patients it was built on. This checks the published exclusions, the dose, the weight and the timing, and tells you whether the chart can be used at all. It does not read the level off the chart, because the paper publishes the lines only as a picture.
Hartford nomogram applicability
Patient + dose + timing → can the chart be used?Adult, none of the exclusions, gentamicin 7 mg/kg on actual weight, level at 9 hours from the start, CrCl 60 mL/min or more
The Hartford program (Nicolau 1995)
Level: one random level 6 to 14 hours after the start of the infusion
Starting interval: CrCl 60 or more → q24h · 40–59 → q36h · 20–39 → q48h · below 20 → dose and follow levels
Above the chart: stop scheduled doses; redose when the level is below 1 mg/L
- the lines
- two regression lines on a figure; the paper gives no equations and no values at 6 or 14 hours, so this page does not reproduce them
- exclusions
- ascites, burns over 20%, pregnancy, end-stage renal disease, enterococcal endocarditis, children
Worked example
Adult, none of the exclusions, gentamicin 7 mg/kg on actual weight, level at 9 hours from the start, CrCl 60 mL/min or more
No published exclusion applies
Gentamicin at 7 mg/kg on the right weight, level inside the 6–14 hour window
CrCl 60 mL/min or more → starting interval q24h
Plot the level on the published figure to confirm or change the interval
When the Hartford nomogram does not apply
| Situation | Why | Source |
|---|---|---|
| Pregnancy, burns over 20%, ascites, dialysis or end-stage renal disease, enterococcal endocarditis, children | Excluded from the program: altered volume or clearance, or a different dosing aim | Nicolau 1995 |
| Dose other than 7 mg/kg | The lines assume 7 mg/kg | Nicolau 1995 |
| Amikacin or another aminoglycoside | Figure is for gentamicin and tobramycin | Nicolau 1995 |
| Level outside 6–14 hours from the start of the infusion | No lines outside the window | Nicolau 1995 |
| CrCl below 20 mL/min | No interval assigned; dose and follow levels | Nicolau 1995 |
| CrCl below 30 mL/min, rapidly changing renal function, any gram-positive synergy | Institutional additions | Stanford Health Care protocol |
A chart with two lines, and a list of people it was not drawn for
The Hartford nomogram is one of the most used charts in hospital pharmacy. Nicolau and colleagues gave 7 mg/kg of gentamicin or tobramycin once, took one random level between 6 and 14 hours after the start of the infusion, and read the interval — every 24, 36 or 48 hours — from where the level fell between two lines. Across 2,184 adults, nephrotoxicity was 1.2%. The appeal is obvious: one level, one chart, one answer.
This page does not reproduce the chart as numbers, and the reason is worth stating. The 1995 paper presents the lines as a figure. It gives no equations and no concentrations at 6 or 14 hours, only a description of regression lines drawn through extrapolated levels from 20 patients plus simulation. Every table of Hartford values in circulation is someone’s reading of that picture. Reading a picture by eye and turning it into a calculator produces a confident interval with an unknown error, for a drug whose toxicity is cumulative. So the level is read on the published figure, and this page answers the question that comes first: can the figure be used for this patient at all?
It often cannot. The program excluded pregnancy, burns over 20% of body surface area, ascites, end-stage renal disease and enterococcal endocarditis, and enrolled no children. The lines only mean anything after exactly 7 mg/kg, calculated on actual weight or — above 20% over ideal — on ideal plus 40% of the excess. The level has to be timed from the start of the infusion, not the end. Below a clearance of 20 mL/min the program assigned no interval at all. When any of these fails, the right move is individualised dosing from two levels, which the aminoglycoside half-life calculator calculates, and a conversation with pharmacy. The dosing weight selection page and adjusted body weight calculator check the dosing weight, and the gentamicin unit converter converts levels reported in µmol/L.
Frequently asked questions
What is the Hartford nomogram?
A chart from Nicolau and colleagues (1995) for once-daily gentamicin or tobramycin at 7 mg/kg. One random level taken 6 to 14 hours after the start of the infusion is plotted against time, and where it falls between two lines sets the dosing interval at every 24, 36 or 48 hours. A level above the chart means stopping scheduled doses and following levels until below 1 mg/L.
Who should not be dosed with the Hartford nomogram?
The published program excluded pregnancy, burns over 20% of body surface area, ascites, end-stage renal disease such as dialysis, enterococcal endocarditis and children. It also only applies to gentamicin and tobramycin at 7 mg/kg, with a level timed 6 to 14 hours from the start of the infusion. Many institutions add further exclusions, such as a creatinine clearance below 30 mL/min or rapidly changing renal function.
Can I use the Hartford nomogram after a 5 mg/kg gentamicin dose?
No. The lines assume 7 mg/kg; after a lower dose every level plots low and suggests a shorter interval than the patient needs. Separate nomograms for lower doses exist, but they are different charts. Ask pharmacy, or calculate the half-life from two levels.
Why doesn’t this page read my level off the nomogram?
Because the original paper publishes the two lines only as a figure, with no equations and no values at the ends of the 6 to 14 hour window. Any numeric version is a reading of that picture by eye, with an error nobody has measured. For a drug with cumulative kidney and ear toxicity, this page checks whether the chart applies and sends you to the published figure to read it.
Which weight should the 7 mg/kg dose be based on?
Actual body weight, unless the patient is more than 20% over ideal body weight, in which case the Hartford program used ideal weight + 0.4 × (actual − ideal). An obese patient given 7 mg/kg of actual weight has received more than the chart assumes, and the level will read high.
Related calculators
References
- Nicolau DP, Freeman CD, Belliveau PP, Nightingale CH, Ross JW, Quintiliani R. Experience with a once-daily aminoglycoside program administered to 2,184 adult patients. Antimicrob Agents Chemother. 1995;39(3):650–655. Fixed 7 mg/kg dose; actual body weight unless the patient was obese ("20% over ideal body weight"), when the dose-determining weight was ideal body weight + 0.4 × (actual − ideal); a single level 6–14 hours after the start of the infusion read against the Hartford nomogram; ascites, burns over 20% of body surface area, pregnancy, end-stage renal disease and enterococcal endocarditis excluded, as were children.
- Stanford Health Care. Aminoglycoside dosing guideline (Antimicrobial Stewardship Program). An institutional protocol: Devine for heights over 60 inches with 45 kg for women; total body weight unless obese, then ideal + 0.4 × excess; Cockcroft-Gault on ideal or adjusted weight; extended-interval dosing avoided in pregnancy, gram-positive synergy, ascites, burns over 20% and creatinine clearance below 30 mL/min or rapidly declining renal function.
- Bauer LA, Edwards WA, Dellinger EP, Simonowitz DA. Influence of weight on aminoglycoside pharmacokinetics in normal weight and morbidly obese patients. Eur J Clin Pharmacol. 1983;24(5):643–647. The origin of the 0.4 correction factor in adjusted body weight.
Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.