What is the recommended dosage of Amikacin (an aminoglycoside antibiotic) for adults?

Adult Dosage of Amikacin

For adults with normal renal function, administer amikacin 15 mg/kg/day intravenously or intramuscularly, divided into 2 or 3 equal doses (7.5 mg/kg every 12 hours or 5 mg/kg every 8 hours), with a maximum total daily dose not exceeding 15 mg/kg/day or 1.5 grams/day. 1

Standard Dosing Regimens

Once-Daily Dosing (Preferred for Most Infections)

• Administer 15 mg/kg as a single daily dose for severe infections, which provides optimal concentration-dependent bactericidal activity and may reduce nephrotoxicity compared to divided dosing 2, 3, 4
• This regimen achieves peak concentrations of 40-45 mg/L and trough concentrations of 1-2 mg/L 5
• Clinical cure rates of 83% have been demonstrated with once-daily dosing, superior to twice-daily regimens (66% cure rate) 4
• Once-daily dosing results in significantly less nephrotoxicity (21% vs 35% with twice-daily dosing) 4

Divided Dosing (Alternative Approach)

• 7.5 mg/kg every 12 hours or 5 mg/kg every 8 hours for standard infections 1
• This achieves average peak concentrations of 28 mg/L and trough concentrations of 5 mg/L 5
• Only 48% of adult patients achieve therapeutic peak concentrations with twice-daily dosing, compared to 100% with once-daily dosing 6

Special Infection-Specific Dosing

• For plague treatment: 15-20 mg/kg every 24 hours IV or IM 2
• For complicated intra-abdominal infections: 15-20 mg/kg every 24 hours 2
• For uncomplicated urinary tract infections: 250 mg twice daily may be sufficient 1

Age-Related Dose Adjustments

Elderly Patients (>59 Years)

• Reduce dose to 10-11 mg/kg/day when using once-daily dosing 7, 8
• Elderly patients have prolonged elimination half-lives (mean 4.8 hours vs 2 hours in younger adults) 8
• Creatinine clearance correlates better with amikacin clearance (r=0.89) than with half-life (r=0.71) in this population 8

Renal Impairment Dosing

Dosing Interval Extension Method

• Calculate dosing interval by multiplying serum creatinine (mg/dL) by 9 1
• Example: If serum creatinine is 2 mg/dL, administer 7.5 mg/kg every 18 hours 1

Dose Reduction Method

• Administer loading dose of 7.5 mg/kg, then reduce maintenance doses proportionally 1
• Maintenance dose = (observed creatinine clearance / normal creatinine clearance) × loading dose 1
• For severe renal impairment: reduce frequency to every 2-3 days at 12-15 mg/kg 7

Hemodialysis Patients

• Administer after dialysis to facilitate directly observed therapy and prevent premature drug removal 7, 1

Obese Patients

• Calculate dose using: ideal body weight + 40% of excess weight 7
• Standard weight-based dosing may lead to underdosing in obese patients 9

Administration Guidelines

Intravenous Administration

• Infuse over 30-60 minutes in adults 1, 3
• Add 500 mg vial to 100-200 mL of compatible diluent (0.9% sodium chloride or 5% dextrose) 1
• Solutions stable for 24 hours at room temperature at concentrations of 0.25-5 mg/mL 1

Intramuscular Administration

• Same dosing as IV route 1
• Administer as deep intramuscular injection 1

Therapeutic Drug Monitoring

Target Concentrations

• Peak levels (once-daily): 65-80 mg/L for intermittent dosing or 25-35 mg/L for daily dosing 7, 9
• Trough levels: <5 mg/L to prevent toxicity 7, 9
• Peak levels >35 mg/L should be avoided to reduce toxicity risk 1

Monitoring Schedule

• Measure peak levels within the first week of therapy 7, 9
• Measure trough levels weekly for 4 weeks, then every 2 weeks when stable 7, 9
• Monitor renal function monthly during treatment 9
• Perform baseline audiometry and intermittent monitoring to detect ototoxicity (defined as 20 dB loss at one frequency or 10 dB loss at two adjacent frequencies) 9

Duration of Therapy

• Standard duration: 7-10 days 1
• For complicated infections: 4-7 days when adequate source control is achieved 2
• If treatment beyond 10 days is required, re-evaluate necessity and monitor serum levels, renal function, and auditory/vestibular function closely 1

Critical Warnings

Nephrotoxicity Risk

• Occurs in approximately 8.7% of patients receiving standard amikacin dosing 10
• Risk increases with trough levels >5 mg/L 7, 9
• Once-daily dosing reduces nephrotoxicity compared to divided dosing 4

Ototoxicity Risk

• Both auditory and vestibular toxicity can occur 5
• Requires baseline and periodic audiometric monitoring 9
• Risk increases with prolonged therapy and elevated trough concentrations 5

Pregnancy Contraindication

• Amikacin is contraindicated in pregnancy due to risk of fetal nephrotoxicity and congenital hearing loss 7, 10

Common Pitfalls to Avoid

• Do not use fixed 500 mg doses regardless of patient weight, as this ignores weight-based dosing principles and risks treatment failure 9
• Do not use every-other-day dosing for IV amikacin in most clinical scenarios, as this may lead to inadequate drug exposure 9
• Do not exceed 15 mg/kg/day total daily dose by all routes of administration 1
• Do not physically premix amikacin with other drugs; administer separately 1
• Do not continue therapy without clinical response after 3-5 days; recheck antibiotic susceptibility 1