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Printed on 6/29/2026
For informational purposes only. This is not medical advice.
This calculator estimates initial gentamicin dosing based on body weight and renal function. Extended-interval dosing (5–7 mg/kg q24–48h) is preferred for most indications. Traditional dosing (1.5–2 mg/kg q8–12h) may be used for specific infections. Always monitor drug levels. Calculate Creatinine Clearance (required input) with [CrCl Calculator](/tools/creatinine-clearance) or [24-Hour Creatinine Clearance](/tools/creatinine-clearance-24h). Monitor for AKI with [eGFR Calculator](/tools/egfr-calculator) and [BUN/Creatinine Ratio](/tools/bun-creatinine-ratio). For MRSA coverage instead, use [Vancomycin AUC/MIC Calculator](/tools/vancomycin-dosing).
Formula: Extended: 5 mg/kg IV, interval by CrCl (q24–48h). Traditional: 1.7 mg/kg IV q8–12h adjusted for renal function.
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Input the patient's adjusted body weight (ABW) — use actual body weight for patients within 20% of ideal body weight; for obese patients use ABW = IBW + 0.4 × (actual − IBW). Enter age, sex, and serum creatinine to calculate creatinine clearance via Cockcroft-Gault, which determines the dosing interval for extended-interval therapy.
Choose extended-interval dosing (5–7 mg/kg IV once daily) for most gram-negative infections — this exploits concentration-dependent killing and the post-antibiotic effect. Adjust interval based on CrCl: CrCl >60 = q24h; 40–59 = q36h; 20–39 = q48h. Choose traditional 3-times-daily dosing (1–1.7 mg/kg q8h) for endocarditis synergy, pregnancy, and patients with ascites or extensive burns.
For extended-interval dosing: draw a single serum level 6–14 hours post-dose (the Hartford nomogram window). If the level falls below the nomogram line, the q24h interval is safe. If above the line, extend to q36h or q48h based on the nomogram. For traditional dosing: obtain peak (30–60 min post-infusion) targeting 5–10 mg/L and trough (<30 min pre-dose) targeting <2 mg/L.
Infectious Disease & Hospitalists
First-line empiric coverage for gram-negative bacteremia, often combined with a beta-lactam for synergy. Extended-interval dosing (5 mg/kg q24h) achieves a high peak-to-MIC ratio exploiting concentration-dependent bactericidal activity against Enterobacteriaceae and Pseudomonas aeruginosa.
Emergency Medicine & Urology
Single-dose or short-course extended-interval gentamicin is a cost-effective option for uncomplicated pyelonephritis, especially in penicillin-allergic patients. Single 5–7 mg/kg IV dose then oral step-down is guideline-supported in selected patients.
Cardiology & Infectious Disease
Low-dose gentamicin synergy (1 mg/kg q8h) is used with a cell-wall active agent (penicillin, ampicillin) for streptococcal and enterococcal endocarditis. Traditional TID dosing is required here — extended-interval is not appropriate for this indication. Note: gentamicin synergy is no longer recommended for S. aureus endocarditis (per IDSA 2009).
Surgery & Critical Care
Gentamicin combined with metronidazole or a beta-lactam/beta-lactamase inhibitor provides broad gram-negative and anaerobic coverage for intra-abdominal infections. Extended-interval preferred in patients with normal or mildly impaired renal function.
Pulmonology & CF Centers
Aminoglycosides (typically tobramycin, sometimes gentamicin) are key for Pseudomonas aeruginosa exacerbations in CF. CF patients have altered pharmacokinetics with increased volume of distribution and clearance — doses of 8–10 mg/kg/day are common. Tobramycin is typically preferred over gentamicin in CF due to higher intrinsic activity against mucoid Pseudomonas.
Pulmonology & Critical Care
As part of combination therapy for hospital-acquired or ventilator-associated pneumonia when Pseudomonas or other drug-resistant gram-negatives are suspected. Combined with a broad beta-lactam. Duration should be as short as clinically feasible to minimize nephrotoxicity.
Meta-analyses consistently show that extended-interval aminoglycoside dosing (once-daily) has equivalent or better efficacy and less nephrotoxicity compared to traditional TID dosing for most indications. The pharmacodynamic rationale: aminoglycosides are concentration-dependent killers — a high peak kills better than sustained moderate levels.
Traditional 3x/day dosing is required for: (1) endocarditis synergy (streptococcal/enterococcal) — extended-interval is not validated here; (2) pregnancy — limited safety data; (3) extensive burns or significant ascites — altered pharmacokinetics require individualized TDM.
Nephrotoxicity risk correlates with trough exposure (time above the nephrotoxicity threshold) — keep traditional troughs <2 mg/L. Monitor serum creatinine every 48–72 hours during therapy. If SCr rises ≥50% from baseline: consider dose reduction, interval extension, or discontinuation. Reassess necessity of aminoglycoside therapy.
Aminoglycoside cochlear toxicity (high-frequency hearing loss) is permanent and cumulative. Risk is highest with prolonged therapy (>7 days), elevated trough levels, and concurrent loop diuretics (furosemide). Limit course duration where possible. Consider baseline and post-treatment audiometry for patients receiving >7–10 days of therapy.
Furosemide and other loop diuretics synergistically increase both nephrotoxicity and ototoxicity risk when combined with aminoglycosides. When co-administration is unavoidable, monitor renal function more frequently and consider alternative analgesics/diuretics if possible.
Gentamicin distributes into lean tissue. Using actual body weight in obese patients leads to overdose and toxicity. Adjusted body weight = IBW + 0.4 × (actual weight − IBW). This accounts for the partial distribution into adipose tissue.
Hospitalized patients, especially those with sepsis or AKI, may have rapidly changing creatinine. Recalculate CrCl and adjust gentamicin dosing whenever SCr changes by >25% from baseline. A dose that was appropriate on day 1 may be toxic by day 3 in a patient developing AKI.
Avoid or minimize concurrent use of vancomycin, NSAIDs, IV contrast, and other nephrotoxins during aminoglycoside therapy. When vancomycin and gentamicin are both required, monitor renal function daily. Consider whether both are truly necessary.
For extended-interval dosing, the Hartford nomogram level (not a true peak) guides interval selection. For traditional dosing: peak targets are 5–10 mg/L for gram-negative infections and 3–5 mg/L for low-dose endocarditis synergy. Higher peaks (8–10 mg/L) may be needed for serious infections like bacteremia or pneumonia.
Aminoglycoside-related nephrotoxicity and ototoxicity are time- and exposure-dependent. Keep courses as short as clinically feasible. Many gram-negative infections can be stepped down to oral fluoroquinolones or beta-lactams after culture sensitivities confirm susceptibility, allowing aminoglycoside discontinuation.
Extended-interval aminoglycoside dosing meta-analysis: Nicolau et al. (Antimicrob Agents Chemother 1995) and Barza et al. (BMJ 1996): equivalent efficacy with reduced nephrotoxicity vs traditional dosing. Hartford Nomogram: Nicolau et al. (Antimicrob Agents Chemother 1995). IDSA Endocarditis Guidelines recommend low-dose gentamicin synergy for streptococcal endocarditis (Baddour et al., Circulation 2015). IDSA 2009 noted gentamicin synergy not recommended for S. aureus endocarditis (Wilson et al.). Renal toxicity: Mingeot-Leclercq & Tulkens (Antimicrob Agents Chemother 1999).
Your calculated gentamicin dose provides an initial starting point based on body weight and renal function. For extended-interval dosing, the typical dose is 5-7 mg/kg of adjusted body weight given intravenously once daily. The dosing interval is determined by creatinine clearance: every 24 hours for CrCl above 60 mL/min, every 36 hours for CrCl 40-60 mL/min, and every 48 hours for CrCl 20-40 mL/min. For CrCl below 20 mL/min, extended-interval dosing is generally not recommended and traditional dosing with level monitoring should be used.
For traditional dosing, the typical dose is 1.5-2 mg/kg every 8-12 hours with target peak levels of 5-10 mcg/mL and trough levels below 2 mcg/mL. This is an initial estimate only. Therapeutic drug monitoring (TDM) with measured serum levels is essential for all patients receiving gentamicin, as individual pharmacokinetics vary significantly based on volume of distribution, renal function changes, and other factors.
Use this calculator when initiating gentamicin therapy for serious gram-negative infections such as pyelonephritis, intra-abdominal infections, bacteremia, or as part of combination therapy for endocarditis (synergy dosing). Extended-interval dosing is the preferred method for most indications due to its favorable pharmacodynamic profile (concentration-dependent killing and prolonged post-antibiotic effect) and potentially reduced nephrotoxicity.
Traditional dosing should be selected for specific clinical scenarios: infective endocarditis (where synergy dosing of 1 mg/kg q8h is standard), pregnancy (limited safety data for extended-interval dosing), patients with extensive burns (altered volume of distribution and enhanced clearance), patients with significant ascites, and patients receiving hemodialysis. Always obtain baseline renal function before starting therapy.
This calculator provides initial dose estimates only and cannot replace therapeutic drug monitoring. Gentamicin has a narrow therapeutic index, and individual pharmacokinetics are highly variable. Factors not captured by this calculator include third-spacing (ascites, pleural effusions), burn injury (which increases volume of distribution and clearance), critical illness hemodynamics, and concurrent nephrotoxic medications.
The calculator uses adjusted body weight, but weight-based dosing assumes a standard volume of distribution of 0.25-0.3 L/kg, which may be significantly altered in critically ill patients. Renal function can change rapidly during treatment, requiring dose re-adjustment. Extended-interval dosing nomograms (such as the Hartford nomogram) require a measured level at a specific time point (typically 6-14 hours post-dose) to verify appropriate clearance, and this calculator does not replace that monitoring step. For patients on renal replacement therapy, dosing must be individualized based on the dialysis modality and schedule.
Disclaimer: This tool is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with questions about your health.
April 21, 2026 · trust-baseline
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