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.