What is the appropriate dose of Amikacin (an aminoglycoside antibiotic) for a patient with impaired renal function (creatinine level 2.2 mg/dL) and a weight of 62 kg?

Amikacin Dosing for Impaired Renal Function

For a patient with a creatinine of 2.2 mg/dL and weight of 62 kg, the appropriate amikacin dose is a loading dose of 7.5 mg/kg (465 mg) followed by maintenance doses of 12-15 mg/kg (744-930 mg) administered two to three times per week (not daily). 1, 2

Dosing Calculation and Rationale

Initial Loading Dose

• Calculate loading dose based on actual body weight: 62 kg × 7.5 mg/kg = 465 mg
• This loading dose is necessary to achieve therapeutic concentrations initially 2

Maintenance Dosing

1. Frequency adjustment: With creatinine of 2.2 mg/dL, dosing should be reduced to 2-3 times weekly instead of daily 1
2. Dose calculation: 12-15 mg/kg per dose (744-930 mg)
3. Administration timing: Give after hemodialysis if patient is receiving dialysis 1

Alternative Dosing Method (Fixed Interval)

If using a fixed interval approach with the normal dose (7.5 mg/kg):

• Calculate interval: Serum creatinine × 9 = 2.2 × 9 = 19.8 hours
• Therefore, administer 465 mg approximately every 20 hours 2

Monitoring Recommendations

1. Serum drug concentrations:

   • Measure peak concentrations 30-90 minutes after infusion
   • Target peak: 20-35 μg/mL
   • Avoid peak concentrations >35 μg/mL
   • Target trough: <10 μg/mL (preferably <5 μg/mL) 2

2. Renal function monitoring:

   • Monitor serum creatinine regularly
   • Be alert for further deterioration in renal function 2, 3

3. Ototoxicity monitoring:

   • Assess for hearing loss, tinnitus, or vestibular dysfunction
   • Higher risk in patients with pre-existing renal impairment 1

Important Considerations

• Concentration-dependent bactericidal effect: Maintaining adequate peak concentrations is critical for efficacy, which is why the dose is kept at 12-15 mg/kg but the frequency is reduced 1

• Risk of accumulation: Patients with impaired renal function may experience increasing half-life of amikacin during therapy, requiring dose adjustments 3

• Administration method: Intravenous administration should be over 30-60 minutes 2

• Duration of therapy: Limit treatment to 7-10 days when possible to minimize toxicity 2

• Early optimization: Achieving optimal peak/MIC ratio early in therapy is associated with better clinical and microbiological outcomes 4

Potential Adverse Effects to Monitor

• Nephrotoxicity: More common in patients with pre-existing renal impairment
• Ototoxicity: Can cause permanent hearing loss or vestibular dysfunction
• Neurotoxicity: Rare but can occur, especially at high serum concentrations

Remember that amikacin is almost exclusively eliminated by the kidneys, making dosage adjustments essential in patients with renal impairment to prevent drug accumulation while maintaining therapeutic efficacy 1, 2.