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Gentamicin injection is indicated for the following conditions, when caused by susceptible organisms;
1. Urinary tract infections; (Not indicated for the treatment of uncomplicated urinary tract infections).
2. Systemic infections, e.g. Septicaemia, peritonitis;
3. Bone and soft-tissue infections, e.g. osteomyelitis, wound and soft-tissue infections.;
4. Infected burns;
5. Infections of the respiratory tract e.g. Pneumonia.
Hypersensitivity to gentamicin is a contraindication to its use. A history of hypersensitivity or serious toxic reactions to other aminoglycosides may contraindicate use of gentamicin because of the known cross-sensitivity of patients to drugs in this class.
It can produce irreversible, cumulative ototoxicity affecting both the cochlea (manifest as hearing loss of higher tones) and more common, the vestibular system (manifest as dizziness and vertigo). Concurrent use of an anti-emetic eg. dimenhydrinate may mask the early symptoms of vestibular ototoxicity.
Reversible nephrotoxicity may occur and acute renal failure has been reported, often in association with the concurrent administration of other nephrotoxic agents eg. other aminoglosides, vancomycin, some cephalosporins, or potentially ototoxic agents such as ethacrynic acid and furosemide.
Renal impairment is usually mild, although acute tubular necrosis and interstitial nephritis have occurred. Decreased glomerular filtration rate is usually seen only after several days, and may even occur after therapy has been discontinued.
Aminoglycosides possess a neuromuscular blocking action and respiratory depression and muscular paralysis have been reported and care is required when another neuromuscular blocking agent is given concomitantly. Neurotoxicity has occurred, both peripheral neuropathies and central symptoms including encephalopathy, confusion, lethargy, hallucinations, convulsions and central depression.
Cross-sensitivity may occur between aminoglycosides. Hypersensitivity reactions, anaphylactic reactions and endotoxic shock has been reported. Infrequent effects reported include blood dyscrasias, purpura, nausea and vomiting, stomatitis, and signs of liver dysfunction eg. increased serum aminotransferase values and increased serum - bilirubin concentrations. Great care is required in patients with myasthenia gravis, parkinsonism and other conditions characterised by muscle weakness. It is desirable to determine dosage requirements by individual monitoring. Dosage should be adjusted to avoid peak plasma concentrations above 10 to 20 µg/mL, or trough concentrations exceeding 2 µg/ml. Monitoring is important in patients receiving high doses or prolonged courses, in infants and the elderly and in patients with renal failure.
Use of aminoglycosides during pregnancy may damage the 8th cranial nerve of the foetus.
Some affected drugs include: amikacin, tobramycin, amphotericin B, cidofovir, cisplatin, polymyxin B, cephalosporins such as cephaloridine, nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen, "water pills"/diuretics such as furosemide, among others. Although most antibiotics probably do not affect hormonal birth control such as pills, patch, or ring, some antibiotics may decrease their effectiveness.
Precautions & Warning:
Due to the risk of ototoxicity and neurotoxicity with prolonged use of aminoglycosides, gentamicin must be restricted to the therapy of life-threatening infections in which a less toxic antimicrobial agent is not suitable. Serum peak levels of 10 µg/mL must be avoided as this could be toxic. Serum trough levels of more than 2 µg/mL may be the best indication of accumulation of gentamicin which may be associated with toxicity.
To ensure safe and effective therapy, dosages should be monitored with serum peak and trough levels. Where practical, regular determination of plasma creatinine levels is advised.
Toxic levels may be reached when gentamicin is administered in normal doses to patients with impaired renal function.