Aminoglycoside Dosing Calculator

Traditional multiple-daily dosing is preferred for: endocarditis (synergy dosing with beta-lactams), pregnancy, burns >20% BSA, cystic fibrosis, ascites/large volume of distribution states, pediatric patients in some protocols, and CrCl <20 mL/min or dialysis patients.

Aminoglycosides are hydrophilic and distribute primarily into lean body mass and extracellular fluid. Adipose tissue has limited aminoglycoside penetration (~40% compared to lean tissue). Using actual body weight in obese patients would overdose them; ABW = IBW + 0.4 × (ABW - IBW) corrects for partial adipose distribution.

The Hartford nomogram is a graphical tool for monitoring extended-interval aminoglycoside dosing. A single random drug level drawn 6-14 hours post-dose is plotted against time to determine if the current dosing interval (q24h, q36h, or q48h) is appropriate. It simplifies monitoring by requiring only one level instead of peak and trough.

Nephrotoxicity (5-25% incidence): rising creatinine, typically reversible. Ototoxicity (cochlear: high-frequency hearing loss, often irreversible; vestibular: dizziness, vertigo, ataxia). Neuromuscular blockade: rare, associated with rapid IV push or concurrent neuromuscular blocking agents. Monitor creatinine daily and audiometry for courses >5-7 days.

Aminoglycoside duration should be minimized to reduce toxicity risk. Most indications require 3-5 days of empiric coverage, stepping down to less toxic alternatives based on culture susceptibility. Prolonged courses (>7 days) significantly increase nephrotoxicity and ototoxicity risk and require daily creatinine monitoring and audiometry.

Concurrent nephrotoxins (vancomycin, amphotericin B, NSAIDs, IV contrast, loop diuretics) significantly increase nephrotoxicity risk. When combination therapy is necessary, more frequent renal monitoring (daily creatinine), aggressive hydration, and shorter aminoglycoside courses are essential risk mitigation strategies.

For hemodialysis: administer the full dose post-dialysis (aminoglycosides are ~50-70% dialyzed). Redose based on pre-dialysis levels. For CRRT: dosing depends on the CRRT modality and flow rates; typically 5-7 mg/kg q24-48h with level-guided adjustment. Close collaboration with clinical pharmacy is essential.

The post-antibiotic effect (PAE) is continued bacterial suppression after drug levels fall below the MIC. Aminoglycosides exhibit a PAE of 2-8 hours against gram-negative organisms, which supports extended-interval dosing. During the PAE period, bacterial regrowth is suppressed even without drug present, extending the effective duration of each dose.

Level monitoring is recommended for: therapy exceeding 48-72 hours, renal impairment, obesity, pregnancy, critically ill patients with fluctuating renal function, concurrent nephrotoxins, and traditional dosing regimens. For empiric short courses (≤48 hours) in patients with stable normal renal function, monitoring may not be necessary.