- Select the drug group: gentamicin/tobramycin (7 mg/kg extended-interval) or amikacin (15 mg/kg extended-interval).
- Choose the dosing strategy: extended-interval (once-daily, Hartford-style) or conventional multiple-daily dosing.
- Select the weight, creatinine, and height units to match your records. Switching a unit clears that field.
- Enter age, sex, and the actual body weight; enter the steady-state serum creatinine (not during AKI).
- Enter height (optional) to compute Devine ideal body weight (IBW) and adjusted body weight — the tool automatically uses the adjusted weight when the patient is obese (actual > 1.2 × IBW), and the lower (actual vs adjusted) otherwise.
- The result shows the Cockcroft-Gault CrCl, the dosing weight used, the recommended mg dose (rounded), and the recommended interval — with monitoring guidance.
All computation runs in your browser; no values are stored or transmitted. This is a starting regimen only — verify against your formulary and mandatory therapeutic drug monitoring.
When to Use
Use this tool to select an initial aminoglycoside regimen — drug dose (mg) and dosing interval — for an adult being treated for a systemic gram-negative infection. The interval is driven by Cockcroft-Gault creatinine clearance, the same equation on which the Hartford extended-interval (once-daily) nomogram and conventional renal-dosing tables were built. Two strategies are supported: extended-interval (high once-daily dose exploiting concentration-dependent killing and the post-antibiotic effect, with prolonged drug-free troughs to limit accumulation/nephrotoxicity) and conventional multiple-daily dosing (lower per-dose, more frequent administration) when extended-interval is inappropriate.
Appropriate population
Adults (≥18 years) with stable renal function being treated for a serious gram-negative infection where empiric aminoglycoside therapy is indicated. Extended-interval dosing is the default for most such patients; conventional dosing is used when extended-interval is contraindicated. Enter height to enable Devine ideal/adjusted body weight, which the tool uses automatically in obesity.
When NOT to use it
Do not use this tool for synergy (gram-positive) dosing — endocarditis and enterococcal synergy use much lower doses (e.g. gentamicin 1 mg/kg q8h targeting peaks ~3–4 mg/L), not the regimens here. Avoid extended-interval dosing in pregnancy, extensive burns, ascites/major fluid shifts, CrCl < 20 mL/min, dialysis, and when synergy dosing is intended — use conventional, level-guided dosing instead. The estimate assumes steady-state creatinine; it is unreliable in AKI or rapidly changing renal function. This calculator never replaces mandatory therapeutic drug monitoring.
Pearls & Pitfalls
Dose by the right weight, then monitor levels
Aminoglycosides distribute mainly in lean tissue, so in obesity dose on adjusted body weight (IBW + 0.4 × [actual − IBW]) rather than actual weight — using actual weight overdoses these patients. This tool applies adjusted weight automatically when actual > 1.2 × IBW. After the first dose, the regimen is confirmed by therapeutic drug monitoring, not by the nomogram alone.
Hartford monitoring for extended-interval
For once-daily (7 mg/kg gentamicin/tobramycin) dosing, draw a single random level 6–14 hours after the first dose and plot it on the Hartford nomogram to confirm or lengthen the interval (q24h / q36h / q48h). The pre-dose trough should be undetectable (< 1 mg/L) — a measurable trough means the interval is too short or clearance has fallen. Amikacin uses the same principle at 15 mg/kg.
Pitfalls
(1) Not for synergy/endocarditis dosing — those use far lower q8h regimens. (2) Do not use fixed extended-interval dosing at CrCl < 20 mL/min, in dialysis, pregnancy, burns, or major fluid shifts — switch to conventional, level-guided redosing. (3) The CrCl estimate is invalid in AKI or rapidly changing renal function. (4) Nephrotoxicity and ototoxicity (often irreversible) rise with duration — keep courses as short as possible and avoid concomitant nephrotoxins. (5) Always confirm dose, interval, and targets against your formulary and TDM service.
Why Use It
Aminoglycosides kill in a concentration-dependent manner and exert a prolonged post-antibiotic effect, so a single high daily dose maximizes the peak-to-MIC ratio (efficacy) while the long drug-free interval allows renal washout that limits the saturable proximal-tubular uptake driving nephrotoxicity. Extended-interval dosing therefore tends to be at least as effective as conventional dosing with comparable or lower toxicity, and it simplifies monitoring to a single nomogram level. Because the therapeutic window is narrow and toxicity is dose- and duration-dependent, getting the initial dose and interval right — adjusted for renal function and the correct dosing weight — protects patients from both treatment failure and avoidable nephro-/ototoxicity. Mandatory drug-level monitoring then individualizes the regimen.
Aminoglycoside Dose & Interval Calculator (by CrCl)
Select the drug and dosing strategy, then enter age, sex, weight, and serum creatinine. The tool computes Cockcroft-Gault CrCl, picks the dosing weight (adjusted body weight in obesity), and returns a recommended mg dose and interval for extended-interval or conventional dosing.
⚕ CrCl by Cockcroft-Gault: [(140 − age) × weight(kg) × (0.85 if female)] / (72 × SCr mg/dL). Dosing weight = adjusted BW (IBW + 0.4×[actual − IBW]) when actual > 1.2 × IBW, else the lower of actual vs adjusted (actual if no height). Extended-interval: gentamicin/tobramycin 7 mg/kg, amikacin 15 mg/kg; interval q24h (CrCl ≥60) / q36h (40–59) / q48h (20–39); CrCl <20 → use conventional level-guided dosing. Conventional: gentamicin/tobramycin ~1.7 mg/kg, amikacin 7.5 mg/kg; interval q8h / q12h / q24h / q48h by CrCl. A starting regimen only — mandatory therapeutic drug monitoring required. Not for synergy/endocarditis dosing. Source: Nicolau DP et al. Antimicrob Agents Chemother. 1995;39(3):650–655 (Hartford nomogram).
Next Steps
Use the result as a starting regimen — then individualize with drug levels.
- Give the calculated dose, then obtain therapeutic drug monitoring: for extended-interval, a single random level 6–14 h after the first dose plotted on the Hartford nomogram; for conventional dosing, a peak and trough around the third dose.
- Target levels — gentamicin/tobramycin: conventional peak 5–10 mg/L, trough < 2 mg/L; amikacin: peak 20–30 mg/L, trough < 10 mg/L. Extended-interval troughs should be undetectable (< 1 mg/L).
- Recheck renal function and creatinine at least every 2–3 days (daily if unstable); recompute the regimen if creatinine changes.
- Keep the course as short as clinically appropriate; reassess the need for the aminoglycoside daily and de-escalate once cultures allow.
- Involve clinical pharmacy / nephrology for CrCl < 20 mL/min, dialysis, rising creatinine, hearing/vestibular symptoms, or pregnancy/burns/major fluid shifts.
Evidence & References
Formula & Equations
| Quantity | Equation |
|---|---|
| Creatinine clearance (mL/min) | [(140 − age) × weight in kg × (0.85 if female)] ÷ (72 × SCr in mg/dL) |
| Ideal body weight — men (Devine) | 50 + 2.3 × (height in inches − 60) |
| Ideal body weight — women (Devine) | 45.5 + 2.3 × (height in inches − 60) |
| Adjusted body weight | IBW + 0.4 × (actual weight − IBW) |
| Dosing weight rule | Adjusted BW when actual > 1.2 × IBW (obesity); otherwise the lower of actual vs adjusted (actual when no height given) |
| SI conversion | SCr (mg/dL) = SCr (µmol/L) ÷ 88.4; weight (kg) = lb ÷ 2.2046; height (in) = cm ÷ 2.54 |
Extended-interval (once-daily) dosing
| CrCl (mL/min) | Interval | Dose (of dosing weight) |
|---|---|---|
| ≥ 60 | q24h | Gentamicin / tobramycin 7 mg/kg · Amikacin 15 mg/kg |
| 40–59 | q36h | |
| 20–39 | q48h | |
| < 20 | Do NOT use fixed extended-interval — switch to conventional, level-guided redosing | |
Conventional (multiple-daily) dosing
| CrCl (mL/min) | Interval | Dose per dose (of dosing weight) |
|---|---|---|
| ≥ 60 | q8h | Gentamicin / tobramycin ~1.7 mg/kg (1.5–2) · Amikacin 7.5 mg/kg |
| 40–59 | q12h | |
| 20–39 | q24h | |
| < 20 | q48h or by levels |
Target levels
| Drug / regimen | Peak | Trough |
|---|---|---|
| Gentamicin / tobramycin — conventional | 5–10 mg/L | < 2 mg/L |
| Amikacin — conventional | 20–30 mg/L | < 10 mg/L |
| Extended-interval (any agent) | Random level on Hartford nomogram (6–14 h post-dose) | Undetectable (< 1 mg/L) |
Doses are rounded to a practical increment (nearest 10–20 mg) and are a starting point only. Confirm against local protocols and adjust to measured drug levels. These regimens are not for synergy/endocarditis dosing, which uses lower doses (e.g. gentamicin 1 mg/kg q8h). KDIGO highlights aminoglycosides as an avoidable cause of nephrotoxic AKI — use the shortest effective course and avoid concomitant nephrotoxins.
Evidence & References
Extended-interval aminoglycoside dosing exploits concentration-dependent killing and the post-antibiotic effect; the Hartford program (Nicolau 1995) standardized a 7 mg/kg once-daily gentamicin/tobramycin regimen with a single nomogram level, achieving efficacy comparable to conventional dosing with low nephrotoxicity. CrCl is estimated by Cockcroft-Gault (1976) and dosing weight by the Devine ideal/adjusted body-weight method (1974). KDIGO cautions that aminoglycosides are a leading reversible/avoidable nephrotoxic insult.
- 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.
- Cockcroft DW, Gault MH. Prediction of Creatinine Clearance from Serum Creatinine. Nephron. 1976;16(1):31–41.
- Devine BJ. Gentamicin Therapy. Drug Intell Clin Pharm. 1974;8(11):650–655.
- Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Int. 2024;105(4S):S117–S314.
