Gentamicin

Oral Antibiotics

Drug class: Aminoglycoside Antibiotics

Gentamicin (Garamycin)（中文：慶大霉素）

Common Strengths

• Injectable Solutions:
  • 40 mg/mL
  • 140 mg/mL
  • 80 mg/2 mL
  • 280 mg/2 mL

Drug Trade Names

Garamycin

Drug Usage

Gentamicin is indicated for the treatment of:

• Blood infections (septicemia)
• Meningitis
• Urinary tract infections (UTIs)
• Lung infections (e.g. pneumonia)
• Skin infections, including severe burns
• Bone and joint infections
• Endocarditis

Mechanism of Action

Gentamicin binds to the 30S ribosomal subunit of bacteria, inhibiting protein synthesis essential for bacterial growth. This binding interferes with the initiation of translation and elongation processes, ultimately leading to bacterial cell death.

Route of Administration

• Intravenous (IV)
• Intramuscular (IM)
• Topical (for skin and eye infections)
• Otic (ear drops)

Dosages

General Dosing Guidelines:

• Adults:
  • Conventional dosing: 3-5 mg/kg/day IV/IM divided every 8 hours.
  • Extended interval dosing: 4-7 mg/kg IV once daily.
• Renal Dosing Adjustments Based on eGFR:
  • CrCl >90 mL/min: every 8 hours
  • CrCl 60-90 mL/min or age ≥60: every 12 hours
  • CrCl 25-60 mL/min: every 24 hours
  • CrCl 10-25 mL/min: every 48 hours
  • CrcL <10 mL/min: every 72 hours

Side Effects

Frequency	Adverse reactions
Common Side Effects	Nausea or vomiting
	Fatigue or tiredness
	Rash or itching
	Pain at the injection site
Serious Side Effects	Nephrotoxicity (kidney damage)
	Ototoxicity (hearing loss)
	Allergic reactions, including anaphylaxis
	Neuromuscular blockade

Pharmacokinetics

Absorption: The aminoglycosides are not absorbed from the gut and must therefore be given by injection for systemic infections. The onset of action for gentamicin:

• After IV administration, gentamicin can begin exerting its effects within 30 minutes, making it suitable for urgent infections where immediate therapeutic action is needed.

Gentamicin has a half-life of approximately:

• IV Administration: ~75 minutes
• IM Administration: ~104 minutes

It is primarily eliminated by the kidneys, with renal clearance correlating closely with creatinine clearance. Monitoring serum levels is crucial to avoid toxicity, especially in patients with renal impairment.

Drug Precautions

Pregnancy

Gentamicin should only be used during pregnancy if the benefits outweigh the risks due to potential fetal harm, including ototoxicity and renal damage.

Breastfeeding

Gentamicin is excreted in breast milk but poses minimal risk to infants when used appropriately. Monitoring may be necessary if the infant has gastrointstinal issues.

Children and Elderly

Caution is advised in children, especially neonates and premature infants. Elderly patients may have increased risk due to potential renal impairment.

Drug Monitoring Items

Monitoring should include:

• Serum creatinine levels
• Auditory functions tests (hearing tests)
• Peak and trough gentamicin levels (target peak: 5-10 mg/L; trough: <2 mg/L for conventional dosing).

Drug Interactions

Gentamicin may interact with various medications, increasing the risk of nephrotoxicity or ototoxicity including:

• Nephrotoxic Agents: The risk of kidney damage is heightened when gentamicin is used alongside other nephrotoxic drugs. Such as:
  • Vancomycin
  • Amphotericin B
  • Cisplatin
  • Indomethacin
  • Loop diuretics (e.g. furosemide, bumetanide) can also increase the risk of nephrotoxicity and ototoxicity.
• Nonsteroidal Anti-Inflammatory Drugs (NASIDs): Medications like ibuprofen and naproxen may reduce the renal clearance of gentamicin, potentially leading to elevated serum levels and increased toxicity.
• Neuromuscular Blocking Agents: Drugs such as pancuronium and atracurium can enhance neuromuscular blockade when used with gentamicin, increasing the risk of respiratory depression.