Gentamicin is a broad-spectrum aminoglycoside antibiotic used to treat serious bacterial infections caused mainly by Gram-negative organisms. It works by inhibiting bacterial protein synthesis, leading to cell death, and is commonly used in conditions such as sepsis, complicated urinary tract infections, and severe respiratory infections, often in hospital settings. Gentamicin was discovered in the early 1960s from the soil bacterium Micromonospora purpurea and was introduced into clinical practice shortly thereafter as part of the aminoglycoside class development, which significantly improved treatment options for severe hospital-acquired infections. Over time, it became an essential antibiotic in critical care due to its strong bactericidal activity, although its use is carefully monitored because of potential kidney and ear toxicity.
BRAND NAMES
Systemic/Injection: Gentamicin brands include Garamycin, Cidomycin, and Septopal.
Ophthalmic (Eye/Ear): Genoptic, Gentak, Garamycin Ophthalmic, Gentacidin, and Gentasol.
Topical: Garamycin Topical and G-Myticin.
Other potential brands: Genticyn, Merigenta, Genta, and Magenta.
MECHANISM OF ACTION
Gentamicin is an aminoglycoside antibiotic that exerts its bactericidal effect by binding irreversibly to the 30S subunit of the bacterial ribosome. This binding interferes with the initiation of protein synthesis and causes misreading of messenger RNA (mRNA), leading to the production of abnormal, nonfunctional proteins. The accumulation of defective proteins disrupts bacterial cell membrane integrity and ultimately results in cell death. Because of this irreversible inhibition of protein synthesis, gentamicin is particularly effective against aerobic Gram-negative bacteria and is often used in severe systemic infections.
PHARMACOKINETICS
Absorption: Peak serum concentration is achieved within 30–90 minutes.
Distribution: Primarily distributed in extracellular fluid (0.22–0.3 L/kg), with low protein binding.
Elimination: Mainly eliminated via the kidneys through glomerular filtration, and clearance is closely related to creatinine clearance.
PHARMACODYNAMICS
Gentamicin is a bactericidal aminoglycoside antibiotic that works by irreversibly binding to the 30S ribosomal subunit, which leads to misreading of mRNA and inhibition of bacterial protein synthesis. It demonstrates concentration-dependent bactericidal activity along with a notable post-antibiotic effect (PAE), meaning its effectiveness depends on achieving high peak serum concentrations in relation to the minimum inhibitory concentration (MIC).
DOSAGE AND STRENGTH
Available strengths: Common injectable concentrations include 10 mg/mL, 40 mg/mL, and 80 mg/2 mL (varies by formulation and brand).
Usual adult dosing (systemic infections):
5–7 mg/kg once daily (extended-interval dosing) OR
1–2 mg/kg every 8 hours (conventional dosing)
Severe infections: Higher doses may be used under strict monitoring of drug levels and kidney function.
Pediatric dosing: Typically 5–7.5 mg/kg/day, adjusted based on age, weight, and infection severity.
Renal impairment: Dose and interval are adjusted according to creatinine clearance.
Administration route: Given intravenously (IV) or intramuscularly (IM); not effective orally for systemic use.
Therapeutic drug monitoring: Peak and trough levels are regularly checked to ensure efficacy and prevent toxicity.
FOOD INTERACTIONS
Gentamicin generally has no significant direct interactions with food, so patients can usually maintain their normal diet. However, because it can affect kidney function, adequate hydration is important during treatment. In some cases, monitoring of electrolytes such as magnesium and calcium may be recommended, and dietary intake of calcium may need attention in susceptible patients.
DRUG INTERACTIONS
Gentamicin is a potent antibiotic with important drug interactions, mainly associated with an increased risk of nephrotoxicity (kidney damage) and ototoxicity (hearing loss). Significant interactions occur with other aminoglycosides, certain antibiotics, and strong diuretics, which can enhance toxicity. In total, more than 200 drugs may interact with gentamicin, so careful monitoring of serum levels and renal function is essential during therapy.
CONTRAINDICATIONS
Gentamicin is contraindicated in individuals with known hypersensitivity to gentamicin or other aminoglycosides such as amikacin and tobramycin. It should be used with great caution, or avoided when possible, in patients with myasthenia gravis or severe renal impairment because of the risk of neuromuscular blockade and increased toxicity.
SIDE EFFECTS
Nephrotoxicity
Ototoxicity
Neuromuscular effects
Injection site reactions
Gastrointestinal effects
Allergic reactions
Electrolyte imbalance
Superinfection (Overgrowth of non-susceptible organisms with long-term therapy)
OVERDOSE
An overdose of Gentamicin is a medical emergency that may lead to severe and potentially irreversible nephrotoxicity (kidney damage) and ototoxicity (damage to hearing and balance). Symptoms can include decreased urine output, dizziness, vertigo, and ringing in the ears (tinnitus). There is no specific antidote; management involves immediate discontinuation of the drug, supportive care, and in many cases, urgent hemodialysis to help remove the drug from the bloodstream.
TOXICITY
Gentamicin toxicity is a serious adverse effect that most commonly involves damage to the kidneys (nephrotoxicity) and the inner ear (ototoxicity) due to drug accumulation in these tissues. Clinical features may include vertigo, hearing impairment, tinnitus, ataxia, and signs of renal failure. While kidney toxicity is often reversible after stopping the drug, inner ear damage is frequently permanent.
