Usage
Gentamicin is an aminoglycoside antibiotic prescribed for serious bacterial infections. It is effective against a wide range of gram-negative bacteria, including Pseudomonas aeruginosa, Proteus species, Escherichia coli, Klebsiella pneumoniae, Enterobacter, and Serratia. It also has activity against some gram-positive bacteria, including Staphylococcus aureus (including methicillin-resistant strains).
Pharmacological Classification: Aminoglycoside antibiotic.
Mechanism of Action: Gentamicin inhibits bacterial protein synthesis by irreversibly binding to the 30S ribosomal subunit, leading to misreading of mRNA and ultimately cell death.
Alternate Names
Gentamicin sulfate.
Brand Names: Garamycin, G-mycetin, and others.
How It Works
Pharmacodynamics: Gentamicin exerts a concentration-dependent bactericidal effect. Higher concentrations achieve greater bacterial killing. Post-antibiotic effect is observed, meaning bacterial growth remains suppressed even after serum concentrations fall below the minimum inhibitory concentration (MIC).
Pharmacokinetics:
- Absorption: Poorly absorbed orally; administered parenterally (IV, IM).
- Distribution: Widely distributed in extracellular fluid; low penetration into cerebrospinal fluid, ocular tissues, and bone. Does not readily cross the placental barrier but is found in breast milk.
- Metabolism: Not significantly metabolized.
- Elimination: Primarily excreted unchanged by glomerular filtration.
Mode of Action: Gentamicin binds to the 30S ribosomal subunit of bacteria. This binding interferes with the initiation of protein synthesis, causes misreading of mRNA, and leads to the production of non-functional proteins. This disruption of protein synthesis ultimately results in bacterial cell death. Gentamicin’s action is primarily bactericidal.
Elimination pathways: Renal excretion.
Dosage
Standard Dosage
Adults: 1.5 mg/kg every 8 hours or 5-7 mg/kg once daily (extended-interval dosing), administered IV or IM.
Children: Dosing varies depending on age:
- Neonates (0-7 days): 2.5-4 mg/kg every 12-24 hours
- Infants and children (1 month to 12 years): 2-2.5 mg/kg every 8 hours or 4-7 mg/kg/day, once daily.
Special Cases:
- Elderly Patients: Dosage adjustments based on renal function are essential.
- Patients with Renal Impairment: Reduced dosage and extended dosing intervals based on creatinine clearance (CrCl). Monitor serum gentamicin levels.
- Patients with Hepatic Dysfunction: Usually no dose adjustment is required.
- Patients with Comorbid Conditions: No specific adjustments are mentioned other than renal dysfunction.
Clinical Use Cases:
Dosing adjustments are based on serum levels and the infection’s severity. Extended-interval dosing is preferred in most cases. For specific clinical use cases: consult an infectious disease specialist or refer to local guidelines.
Dosage Adjustments:
Monitor serum gentamicin levels, especially in patients with renal impairment, to ensure therapeutic levels and minimize toxicity. Nomograms or individualized pharmacokinetic monitoring can guide dose adjustments.
Side Effects
Common Side Effects:
- Pain or irritation at the injection site.
- Nausea, vomiting, loss of appetite.
Rare but Serious Side Effects:
- Nephrotoxicity: Renal damage can occur, especially with high doses or prolonged treatment.
- Ototoxicity: Both auditory (hearing loss) and vestibular (balance problems, vertigo) toxicity are possible, especially with pre-existing renal impairment.
- Neuromuscular Blockade: Rarely, respiratory paralysis can occur, especially when given with neuromuscular blocking agents.
Long-Term Effects: Ototoxicity and nephrotoxicity can be irreversible with prolonged or high-dose gentamicin therapy.
Adverse Drug Reactions (ADR): As above.
Contraindications
- Hypersensitivity to gentamicin or other aminoglycosides.
- Myasthenia gravis (relative contraindication).
- Pre-existing hearing loss or vestibular dysfunction (relative contraindication).
Drug Interactions
- Nephrotoxic drugs: Concurrent use with other nephrotoxic agents (e.g., amphotericin B, vancomycin, NSAIDs) increases the risk of renal damage.
- Ototoxic drugs: Concurrent use with other ototoxic drugs (e.g., loop diuretics) increases the risk of hearing loss or balance problems.
- Neuromuscular blocking agents: Gentamicin can potentiate the effects of these agents, increasing the risk of respiratory paralysis.
Pregnancy and Breastfeeding
- Pregnancy: Gentamicin crosses the placenta and can cause fetal harm (ototoxicity, nephrotoxicity). Use only if the potential benefit outweighs the risk to the fetus. Pregnancy category C or D (source dependent).
- Breastfeeding: Gentamicin is excreted in breast milk in low concentrations. Monitor the infant for diarrhea, thrush, and other signs of gastrointestinal disturbance.
Drug Profile Summary
- Mechanism of Action: Inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit.
- Side Effects: Nephrotoxicity, ototoxicity, neuromuscular blockade.
- Contraindications: Hypersensitivity to aminoglycosides, myasthenia gravis.
- Drug Interactions: Nephrotoxic and ototoxic drugs, neuromuscular blocking agents.
- Pregnancy & Breastfeeding: Use with caution in pregnancy (Category C/D); monitor infants for adverse GI effects during breastfeeding.
- Dosage: Adults: 1.5 mg/kg q8h or 5-7 mg/kg q24h; Children: dose varies with age.
- Monitoring Parameters: Serum gentamicin levels, renal function (serum creatinine, urine output), hearing and balance.
Popular Combinations
Gentamicin is often used in combination with beta-lactam antibiotics (e.g., penicillin, ampicillin) for synergistic effects against gram-negative bacteria, especially for serious infections like sepsis or endocarditis.
Precautions
- General Precautions: Renal function monitoring. Hearing and balance assessments. Monitor serum gentamicin levels.
- Specific Populations: As detailed in earlier sections.
- Lifestyle Considerations: No specific lifestyle modifications are mentioned.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Gentamicin?
A: Adults: 1.5 mg/kg IV or IM every 8 hours, or 5–7 mg/kg once daily. Pediatric doses vary depending on age and weight.
Q2: What are the most serious side effects of Gentamicin?
A: Nephrotoxicity (kidney damage) and ototoxicity (hearing loss and balance problems) are the most serious potential side effects.
Q3: How is Gentamicin administered?
A: Gentamicin is usually given intravenously (IV) or intramuscularly (IM). It is not well absorbed orally.
Q4: Can Gentamicin be used during pregnancy?
A: Gentamicin should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. It is classified as Pregnancy Category C or D (source dependent) and can cause fetal harm (ototoxicity and nephrotoxicity).
Q5: Can Gentamicin be used during breastfeeding?
A: Gentamicin is excreted in breast milk in small amounts. Closely monitor the infant for diarrhea, thrush, or other gastrointestinal problems.
Q6: What are the signs of gentamicin toxicity?
A: Decreased urine output, ringing in the ears (tinnitus), hearing loss, dizziness, loss of balance, and persistent nausea or vomiting could indicate toxicity.
Q7: How often should gentamicin levels be monitored?
A: The frequency of monitoring depends on the patient’s renal function and clinical status. Frequent monitoring is essential for patients with renal impairment.
Q8: What infections is Gentamicin commonly used to treat?
A: Gentamicin is used to treat serious bacterial infections, including urinary tract infections, respiratory tract infections, sepsis, endocarditis, and other severe systemic infections caused by susceptible bacteria.
Q9: What drugs interact with Gentamicin?
A: Gentamicin can interact with other nephrotoxic or ototoxic medications, such as certain other antibiotics, loop diuretics, and NSAIDs. It can also interact with neuromuscular blocking agents. Consult drug interaction resources for a complete list.
