Unit Converter
Gentamicin
(Aminoglycoside Antibiotic – Requires Therapeutic Drug Monitoring for Efficacy & Safety)
Synonyms
- Gentamicin
- Gentamycin (incorrect spelling, but commonly seen)
- Aminoglycoside antibiotic
- Genta
Units of Measurement
- µmol/L
- mg/L
- mg/dL
- mg/100 mL
- mg%
- µg/mL
Key Conversions
(Molecular Weight ≈ 477 g/mol)
1 mg/L = 2.096 µmol/L
1 mg/dL = 10 mg/L
1 µg/mL = 1 mg/L
mg/dL = mg% = mg/100 mL
1 µmol/L = 0.477 mg/L
Description
Gentamicin is a broad-spectrum aminoglycoside antibiotic effective against many Gram-negative bacteria and some Gram-positive organisms (in synergy with β-lactams).
It is commonly used for:
- Sepsis
- Pneumonia
- UTI
- Bacteremia
- Endocarditis
- Neonatal infections
Because of its narrow therapeutic index, serum monitoring is essential to prevent kidney and ear toxicity.
Mechanism of Action
Gentamicin:
- Binds to 30S ribosomal subunit
- Inhibits protein synthesis
- Causes bacterial cell death (bactericidal)
Activity is concentration-dependent.
Clinical Significance
Why Gentamicin Levels Must Be Monitored
Aminoglycosides can cause:
- Nephrotoxicity (reversible)
- Ototoxicity (often irreversible)
- Vestibular toxicity
- Neuromuscular blockade (rare)
Therapeutic drug monitoring (TDM) ensures:
- Effective peak levels
- Safe trough levels
Reference Intervals
(Sanford Guide + IDSA + Mayo Labs + Tietz)
Standard Dosing (Multiple Daily)
- Peak: 5–10 mg/L
- Trough: <2 mg/L
Extended-Interval (Once-daily)
Use Hartford Nomogram
- Random level at 6–14 hours → determine interval
Levels typically lower at trough, higher at peak, but nephrotoxicity less common.
Interpretation
High Peaks (>12 mg/L)
- Increased toxicity risk
- Dose too high
- Renal impairment
- Drug accumulation
High Troughs (>2 mg/L)
- Strong predictor of nephrotoxicity
- Must adjust interval
Low Peaks
- Ineffective therapy
- Under-dosing
- Increased bacterial resistance risk
Diagnostic Uses
1. Therapeutic Drug Monitoring in Adults & Children
- Ensure adequate peak concentration
- Avoid nephro- & ototoxicity
2. Neonatal Dosing
Gentamicin widely used in neonates:
- Sepsis
- UTI
- Meningitis (with ampicillin)
Monitor levels due to immature renal function.
3. Renal Impairment
Requires:
- Extended dosing intervals
- Frequent trough monitoring
4. Endocarditis
Synergistic therapy with β-lactam antibiotics:
- Target peak: 3–5 mg/L
- Target trough: <1 mg/L
Analytical Notes
- Immunoassay or HPLC methods used
- Levels drawn:
- Peak: 30 minutes after end of infusion
- Trough: Immediately before next dose
- Peak: 30 minutes after end of infusion
- Hemolysis has minimal effect
- Must coordinate with pharmacy dosing protocol
Clinical Pearls
- Aminoglycosides show post-antibiotic effect, allowing once-daily dosing.
- Trough level is most important predictor of renal toxicity.
- Gentamicin penetrates poorly into CSF; not used alone for meningitis.
- Avoid use with other nephrotoxic drugs (vancomycin, amphotericin, cisplatin).
- Adjust dosing in obesity using adjusted body weight (AdjBW).
Interesting Fact
Gentamicin is derived from Micromonospora purpurea and was discovered in 1963 - revolutionizing treatment of Gram-negative infections.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Drug Monitoring.
- Sanford Guide to Antimicrobial Therapy - Aminoglycosides.
- IDSA Guidelines - Severe Infections & TDM.
- Mayo Clinic Laboratories - Gentamicin.
- ARUP Consult - Aminoglycoside Pharmacokinetics.
- MedlinePlus / NIH - Gentamicin Test.