How to calculate the dose of amikacin?

Amikacin Dosing Guidelines

For optimal outcomes in terms of morbidity and mortality, amikacin should be dosed at 15 mg/kg per day for adults with normal renal function, administered as a single daily dose intravenously or intramuscularly. 1, 2

Standard Dosing Algorithm

Adults with Normal Renal Function

• Standard dose: 15 mg/kg/day (maximum 1.0 g/day)
• Administration: Single daily dose (preferred) via IV or IM route
• Duration: Initially 5-7 days/week, then reducing to 2-3 times weekly after 2-4 months or culture conversion 1
• Age adjustment: For patients >59 years old, reduce to 10 mg/kg/day (maximum 750 mg) 1

Children with Normal Renal Function

• Standard dose: 15-30 mg/kg/day (maximum 1 g/day)
• Administration: Single daily dose via IV or IM route 1

Renal Impairment Dosing Adjustments

Renal function impairment requires careful dosing adjustment as amikacin is cleared almost exclusively by the kidneys 1:

1. Maintain mg/kg dose but extend interval:

   • Calculate interval (hours) = patient's serum creatinine × 9
   • Example: If serum creatinine is 2 mg/dL, give normal dose every 18 hours 2

2. Reduced dose at fixed intervals:

   • Give loading dose of 7.5 mg/kg
   • Calculate maintenance dose (every 12 hours):

     Maintenance dose = (Patient's CrCl ÷ Normal CrCl) × Loading dose

   • Alternative: Divide normal dose by patient's serum creatinine 2

3. For hemodialysis patients:

   • Dose: 12-15 mg/kg 2-3 times weekly
   • Administer after dialysis to prevent drug removal 1

Therapeutic Drug Monitoring

Monitoring serum concentrations is essential to avoid toxicity:

• Peak levels: 30-90 minutes after injection
• Target peak: <35 μg/mL
• Trough levels: Just before next dose
• Target trough: <10 μg/mL 2

Potential Adverse Effects

1. Ototoxicity:

   • Manifests as hearing loss (24% with high-frequency hearing loss in one study) 1
   • Risk factors: Prolonged treatment, higher doses, concurrent diuretic use 1

2. Nephrotoxicity:

   • Occurs in 8.7% of patients overall; 3.4% in patients without risk factors 1
   • Risk factors: Pre-existing elevated creatinine, higher cumulative doses, concomitant nephrotoxic agents 1

Special Considerations

• Pregnancy: Contraindicated due to risk of fetal nephrotoxicity and congenital hearing loss 1
• CNS penetration: Poor penetration into CSF, even with meningitis 1
• Hepatic disease: No dosage adjustments needed 1

Monitoring Recommendations

• Baseline: Audiogram, vestibular testing, Romberg testing, serum creatinine
• Monthly: Renal function assessment, questioning about auditory/vestibular symptoms
• As needed: Repeat audiogram and vestibular testing if symptoms of eighth nerve toxicity develop 1

The advantage of amikacin over other aminoglycosides is the routine availability of serum concentration measurements, which should be utilized whenever possible to guide therapy and minimize toxicity 1.