Which dose per kilogram does this use?

It uses the conventional extended-interval doses: 7 mg/kg for tobramycin (and gentamicin) on the Hartford regimen, and 15 mg/kg for amikacin. Multiplying by the dosing weight gives the single high dose that maximises the concentration-dependent killing of these drugs.

How is the interval chosen?

The Hartford approach gives the dose every 24 hours when creatinine clearance is at least 60 mL/min, every 36 hours from 40 to 59 mL/min, and every 48 hours from 20 to 39 mL/min. Below 20 mL/min extended-interval dosing is not validated and traditional dosing with levels is recommended.

Why not just give the same dose every day?

Aminoglycosides are concentration-dependent and have a post-antibiotic effect, so a single large dose with a drug-free interval maximises bacterial killing while letting the kidney clear the drug between doses, reducing the risk of accumulation and toxicity in patients with reduced clearance.

What weight should I use?

Use ideal body weight, or adjusted body weight if the patient is more than about 20 percent over their ideal weight, because aminoglycosides distribute into lean tissue rather than fat. Using total body weight in obesity overestimates the dose.

Does this replace level monitoring?

No. Extended-interval dosing still requires a timed level interpreted against the relevant nomogram graph to confirm or extend the interval, plus renal-function monitoring. This tool gives the starting dose and interval band only.

Aminoglycoside Extended-Interval Dosing Nomogram

Extended-interval (once-daily) aminoglycoside dosing gives a single large dose with a drug-free interval to exploit concentration-dependent killing while limiting toxicity. This tool computes the tobramycin or amikacin dose from body weight and selects the dosing interval from creatinine clearance using the Hartford nomogram bands.

How it works

The dose is weight-based and the interval is set by kidney function:

Tobramycin / gentamicin dose = 7 mg/kg × dosing weight
Amikacin dose                = 15 mg/kg × dosing weight

Interval by creatinine clearance (CrCl):
  CrCl >= 60 mL/min  -> every 24 hours
  CrCl 40-59 mL/min  -> every 36 hours
  CrCl 20-39 mL/min  -> every 48 hours
  CrCl < 20 mL/min   -> use traditional dosing with levels

Use ideal or adjusted body weight, not total weight, because these drugs distribute into lean tissue. A timed level still confirms or extends the interval.

Example and notes

A 70 kg patient with a creatinine clearance of 50 mL/min started on tobramycin receives 490 mg (7 mg/kg) given every 36 hours. The same patient on amikacin would receive 1050 mg every 36 hours. Round to a practical vial size, draw a nomogram level at the recommended time, and monitor renal function and trough levels throughout the course. Below a clearance of 20 mL/min, switch to traditional dosing rather than relying on this nomogram.