Gentamicin Sulfate
Gentamicin is a potent parenteral **aminoglycoside antibiotic** primarily used for serious gram-negative aerobic bacterial infections. Key pharmacological features include: * **Spectrum of Activity**: Excellent against gram-negative aerobes (e.g., *E. coli, Klebsiella, Proteus, Pseudomonas, Salmonella*) and some staphylococci. It is inactive against anaerobes, fungi, and viruses. * **Concentration-Dependent Bactericidal Activity**: Efficacy is driven by achieving a high peak serum concentration relative to the Minimum Inhibitory Concentration (MIC) of the pathogen. * **Post-Antibiotic Effect (PAE)**: Bacterial growth remains suppressed even after drug concentrations fall below the MIC, which supports the modern practice of **once-daily dosing**. * **Toxicity Profile**: Because of significant risks for **nephrotoxicity** and **ototoxicity**, systemic use is generally reserved for severe infections where less toxic alternatives are ineffective. > **Clinical Pearl**: Risk factors for toxicity include preexisting renal disease, age (neonates and geriatrics), fever, sepsis, and dehydration. Cats are particularly sensitive to the vestibular (ototoxic) effects.
กลไกการออกฤทธิ์: Gentamicin is a **concentration-dependent bactericidal** antibiotic. * **Mechanism**: It actively transports across the bacterial cell membrane via an **oxygen-dependent mechanism** → irreversibly binds to the **30S ribosomal subunit** → causes misreading of mRNA → inhibits bacterial protein synthesis, leading to cell death. * **Environmental Factors**: Antimicrobial activity is significantly enhanced in an **alkaline environment** and inhibited in acidic, purulent, or necrotic environments. * **Resistance**: Because the transport mechanism requires oxygen, **anaerobic bacteria are inherently resistant** to all aminoglycosides.
ขนาดยาตามชนิดสัตว์
- Empiric therapy for susceptible infections · 5-8 mg/kg · IV, SC, IM · q24h · Route not specified in text; assumed IV, SC, IM by Plumb.
- Susceptible infections · 6-8 mg/kg · Not specified · q24h · Neutropenic or immunocompromised patients may need q8h dosing (divided).
- Susceptible infections · 8 mg/kg q24h OR 2-4 mg/kg q8h · IV, IM, SC · q24h or q8h
- Localized, urinary infections · 2.2 mg/kg · IV, IM, SC · q24h · <7 days · Monitor renal function.
- Bacteremia, sepsis · 4.4 mg/kg · IV, IM, SC · q24h · <7 days · Monitor renal function.
- Colibacillosis in neonates · 5 mg · PO, IM · Once · Once · Garacin Pig Pump and Piglet Injection.
- Colibacillosis in weanlings and other swine · 1.1 mg/kg/day in drinking water (concentration of 25 mg/gallon) · PO · Daily · 3 days
- Swine dysentery (Treponema hyodysenteriae) · 2.2 mg/kg/day in drinking water (concentration of 50 mg/gallon) · PO · Daily · 3 days
- Susceptible infections · 5 mg/kg · SC, IM · q24h · Use with caution or avoid use.
วิธีการให้ยา
ข้อห้ามใช้
- Known hypersensitivity to aminoglycosides
- Use with extreme caution in preexisting renal disease
- Use with caution in working dogs (e.g., seeing-eye, herding, hearing-impaired assistance dogs) due to irreversible ototoxicity
- Use with caution in patients with neuromuscular disorders (e.g., myasthenia gravis)
- Do not use in animals with botulism
- Use with caution in rabbits (adversely affects GI flora)
- Use with caution in neonates, geriatrics, and dehydrated patients
- Perforated tympanum (for aural preparations)
- Concurrent use of other nephrotoxic drugs
- Systemic use exceeding 7 days
- Pregnancy
อาการไม่พึงประสงค์
- Nephrotoxicity (tubular necrosis)
- Ototoxicity (auditory and vestibular; cats are highly sensitive to vestibular effects)
- Neuromuscular blockade
- Facial edema
- Pain or inflammation at the injection site
- Peripheral neuropathy
- Hypersensitivity reactions
- Rarely: GI signs, hematologic, and hepatic effects
- Nephrotoxicity (acute tubular necrosis)
- Ototoxicity (auditory and vestibular)
- Neuromuscular blockade (rare)
- Delayed epithelial healing of corneal ulcers (ophthalmic use)
- Local irritation
อันตรกิริยาระหว่างยา
- Beta-lactam antibiotics (penicillins, cephalosporins) · Synergistic effects against some bacteria; however, potential for in vitro inactivation of aminoglycosides (do not mix in the same syringe/bag) and in vivo inactivation in patients with renal failure. · major
- Cephalosporins · Potential additive nephrotoxicity (well documented with older cephalosporins like cephalothin).
- Loop or Osmotic Diuretics (e.g., furosemide, torsemide, mannitol) · Concurrent use may increase the nephrotoxic or ototoxic potential of aminoglycosides.
- Other Nephrotoxic Drugs (e.g., cisplatin, amphotericin B, polymyxin B, vancomycin) · Increased risk for nephrotoxicity.
- Neuromuscular blocking agents & General anesthetics · Concomitant use could potentiate neuromuscular blockade.
- Amphotericin B · Increased risk of nephrotoxicity and ototoxicity · major
- Furosemide · Increased risk of nephrotoxicity and ototoxicity · major
- Heparin · In vitro chemical inactivation (do not mix in same syringe) · major
- Non-depolarizing muscle relaxants (Atracurium, Pancuronium, Vecuronium) · Enhanced neuromuscular blockade · major
การติดตาม
- Clinical efficacy (resolution of clinical signs, negative cultures)
- Renal toxicity: Baseline and ongoing urinalysis (casts in urine are often the initial sign of impending nephrotoxicity), serum BUN, and creatinine
- Gross monitoring for vestibular (balance) or auditory (hearing) toxicity
- Therapeutic Drug Monitoring (TDM): Serum levels drawn at 1, 2, and 4 hours post-dose. Peak should be >20 mcg/mL; 4-hour trough should be <10 mcg/mL
- Urinalysis (monitor for cellular casts as an early indicator of tubular damage)
- Serum creatinine and BUN
- Hydration status
- Therapeutic Drug Monitoring (TDM): Peak >20 μg/ml, Trough <1 μg/ml
- Auditory and vestibular function
การได้รับยาเกินขนาด
In the event of an inadvertent overdose, three treatments are recommended: 1. **Hemodialysis**: Very effective in reducing serum levels, but rarely a viable option in veterinary medicine. 2. **Peritoneal dialysis**: Reduces serum levels but is much less effective than hemodialysis. 3. **Complexation**: Administration of ticarcillin (12-20 g/day in humans) is reportedly nearly as effective as hemodialysis in complexing and deactivating the drug.
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