Is a single dose of gentamicin (an aminoglycoside antibiotic) sufficient for treating Serratia marcescens infections?

Treatment of Serratia marcescens Infections: Multiple Doses of Gentamicin Required

For Serratia marcescens infections, a single dose of gentamicin is NOT sufficient; multiple daily doses are required for effective treatment.

Gentamicin Dosing Recommendations for Serratia marcescens

The American Heart Association guidelines clearly state that gentamicin should be administered in daily multiple divided doses rather than as a single daily dose for serious infections 1. For patients with normal renal function:

• Recommended dosing: 3 mg/kg/day IV divided into multiple doses (typically every 8 hours) 1, 2
• Target serum levels: 1-hour concentration of approximately 3 μg/mL and trough concentration of <1 μg/mL 1
• Duration: Based on the type and severity of infection (typically 7-14 days for most infections)

Why Multiple Doses Are Necessary

1. Pharmacokinetic considerations: Studies comparing single daily dosing versus multiple daily dosing for serious infections have yielded conflicting results 1

2. Guideline recommendations: Until more convincing data demonstrate that once-daily dosing is as effective as multiple dosing, gentamicin should be administered in daily multiple divided doses 1

3. Clinical efficacy: For serious infections like Serratia bacteremia, multiple daily dosing ensures consistent antimicrobial activity throughout the dosing period 2

Serratia marcescens Susceptibility

Recent studies show that Serratia marcescens generally maintains good susceptibility to gentamicin:

• A 2019 study found very low resistance rates (0.6%) to gentamicin among Serratia marcescens isolates 3
• Gentamicin remains one of the most suitable antibiotics for Serratia treatment 3

Monitoring Recommendations

When using gentamicin for Serratia infections:

• Therapeutic drug monitoring: Essential for courses >3 days 2
• Renal function monitoring: Regular assessment of serum creatinine, BUN, and electrolytes 2
• Dose adjustment: Based on changing renal function and drug levels 2

Special Considerations

Renal Impairment

• For patients with creatinine clearance <50 mL/min, dosage adjustment and close serum concentration monitoring are required 1, 2
• For severe renal impairment (creatinine clearance <20 mL/min), consider alternative agents or consult infectious disease specialists 2

Elderly Patients

• Lower doses may be needed (e.g., starting at 10 mg/kg/day divided into multiple doses) 2
• Multiple daily dosing is preferred over once-daily dosing in patients >65 years 2

Common Pitfalls to Avoid

1. Inadequate dosing: Underdosing may lead to treatment failure and resistance development 4
2. Failure to monitor drug levels: Can result in toxicity or subtherapeutic levels 2
3. Overlooking drug interactions: Avoid concurrent use with other nephrotoxic medications when possible 2
4. Assuming once-daily dosing is appropriate for all patients: Multiple daily dosing remains the standard for serious infections 1, 2

Combination Therapy Considerations

For severe or complicated Serratia infections, combination therapy may be considered:

• Gentamicin plus fosfomycin has shown synergistic effects against Serratia 5
• For multi-drug resistant strains, combination therapy may improve outcomes 6, 5

In conclusion, while once-daily aminoglycoside dosing has gained popularity for some indications, current guidelines still recommend multiple daily doses of gentamicin for treating serious infections like those caused by Serratia marcescens.