What is the appropriate dosing and administration of Amikacin (intramuscular injection) for a patient with normal renal function and no history of hearing loss?

Amikacin Intramuscular Dosing and Administration

For adults with normal renal function and no hearing loss, administer amikacin 15 mg/kg/day (maximum 1.0 g/day) intramuscularly as a single daily dose, or divided into 7.5 mg/kg every 12 hours or 5 mg/kg every 8 hours. 1

Standard Dosing Protocol

Adults

• 15 mg/kg/day intramuscularly (maximum 1.0 g/day), administered as a single daily dose 5-7 days per week initially 2, 1
• Alternative divided dosing: 7.5 mg/kg every 12 hours OR 5 mg/kg every 8 hours 1
• For patients >59 years: reduce to 10 mg/kg/day (maximum 750 mg) due to decreased renal reserve 2
• After 2-4 months or culture conversion, frequency can be reduced to 2-3 times weekly depending on efficacy of concurrent medications 2

Children and Infants

• 15-30 mg/kg/day intramuscularly (maximum 1 g/day) as a single daily dose 2
• Newborns: Loading dose of 10 mg/kg, followed by 7.5 mg/kg every 12 hours 1

Duration

• Typical treatment duration: 7-10 days 1
• Limit treatment to short-term whenever feasible 1
• If treatment beyond 10 days is required, reevaluate necessity and intensify monitoring 1

Preparation and Administration

• Available as aqueous solution in 500 mg and 1 g vials for intramuscular injection 2
• Calculate dosing based on pretreatment body weight 1

Target Serum Concentrations

• Peak levels (30-90 minutes post-injection): aim for <35 mcg/mL 1
• Trough levels (just before next dose): maintain <10 mcg/mL 1
• Measure both peak and trough concentrations intermittently during therapy whenever possible 1

Mandatory Baseline and Monitoring Requirements

Before Initiating Therapy

• Baseline audiogram 2, 3
• Vestibular testing and Romberg testing 2, 3
• Serum creatinine measurement 2, 3, 1

During Therapy

• Monthly renal function assessments 2, 3
• Monthly questioning regarding auditory or vestibular symptoms 2, 3
• Repeat audiogram and vestibular testing if any symptoms of eighth nerve toxicity develop 2
• Serum drug concentration monitoring to ensure adequate but not excessive levels 1

Toxicity Profile and Risk Factors

Ototoxicity

• High-frequency hearing loss occurs in up to 24% of patients, with higher rates in those receiving longer treatment or higher cumulative doses 2, 3
• Amikacin causes deafness more commonly than vestibular dysfunction 2
• Risk increases with concurrent diuretic use 2, 3
• Cumulative dose >100-120 g significantly increases risk 2

Nephrotoxicity

• Renal impairment occurs in 8.7% of patients overall 2, 3
• Only 3.4% nephrotoxicity rate in patients without risk factors 3
• Higher frequency in patients with baseline elevated creatinine, larger cumulative doses, and concurrent nephrotoxic agents 2, 3
• Amikacin is more nephrotoxic than streptomycin 2, 3

Critical Clinical Pitfalls to Avoid

Dosing Errors

• Never reduce the milligram dose in patients with any degree of renal impairment—this compromises the concentration-dependent bactericidal effect 4, 3
• Instead, maintain the 12-15 mg/kg dose but extend the dosing interval to 2-3 times weekly 2, 4, 3
• Smaller doses reduce drug efficacy 2

Monitoring Failures

• Failure to obtain baseline audiometry prevents detection of drug-induced hearing loss 2, 3
• Relying on BUN alone is unreliable for assessing renal function—use serum creatinine or creatinine clearance 1

High-Risk Populations

• Elderly patients require dose reduction to 10 mg/kg/day due to age-related decline in renal function 2
• Patients with baseline renal impairment face highest risk for both ototoxicity and nephrotoxicity 3

Absolute Contraindications

• Pregnancy: amikacin is absolutely contraindicated due to risk of fetal nephrotoxicity and congenital hearing loss 2, 3

Clinical Efficacy Data

• In a large multicenter trial of 697 evaluable patients, 81% achieved clinical cure with standard dosing of 7.5 mg/kg every 12 hours intramuscularly 5
• Efficacy rates: 90% for genitourinary infections, 85% for septicemia, 70% for skin/soft tissue/bone infections, and 69% for lower respiratory tract infections 5
• 88% efficacy against gentamicin-resistant pathogens 5
• Uncomplicated infections should respond within 24-48 hours; if no response by 3-5 days, discontinue and recheck susceptibility 1