UVA CLINICAL PHARMACOLOGY / ANTIBIOTICS / GENTAMICIN 1 Adverse Reactions to Gentamicin: Recognition, Treatment, and Prevention Indunil Karunarathna 1 , P Gunasena 1 , S Gunathilake 1 , T Hapuarachchi 1 , U Ekanayake 1 , S Rajapaksha 1 , K Gunawardana 1 , P Aluthge 1 , Sau Bandara 1 , Asoka Jayawardana 1 , Kapila De Alvis 1 1. Ministry of Health / Teaching Hospital Badulla / University of Colombo. Abstract: Gentamicin is an aminoglycoside antibiotic primarily used to treat aerobic gram-negative bacterial infections. Due to its minimal gastrointestinal absorption, gentamicin is administered parenterally via systemic, topical, or ophthalmic routes. It demonstrates bactericidal activity against a broad spectrum of pathogens, including members of the Enterobacteriaceae family, Pseudomonas aeruginosa, and certain strains of Neisseria, Moraxella, and Haemophilus. Clinical use of gentamicin should be guided by culture and susceptibility data, but it can also be indicated based on local epidemiological patterns, particularly in cases of bacterial septicemia, meningitis, urinary tract infections, gastrointestinal infections, and soft tissue infections. This review will outline the indications, mechanism of action, contraindications, and key considerations for gentamicin use, with a focus on administration routes, adverse effects, and the importance of monitoring. Combination therapy, particularly with beta-lactams, is highlighted for its synergistic effects in severe infections such as bacterial endocarditis and enterococcal bacteremia. Keywords: Gentamicin, aminoglycoside antibiotic, gram-negative bacteria, bactericidal, infections, beta-lactam, synergy, parenteral administration, adverse effects, nosocomial infections Key Points: Indications: Gentamicin is indicated for the treatment of bacterial septicemia, meningitis, urinary tract infections, peritonitis, and soft tissue infections caused by gram- negative organisms. Mechanism of Action: Gentamicin works by binding to bacterial ribosomes, inhibiting protein synthesis, and causing bacterial cell death. Combination Therapy: Often combined with beta- lactam antibiotics to increase penetration into bacteria and improve efficacy, especially against gram-positive organisms. Adverse Effects: Nephrotoxicity and ototoxicity are notable adverse effects, necessitating careful monitoring of serum levels. Contraindications and Precautions: Should be avoided in patients with known hypersensitivity to aminoglycosides and used with caution in patients with pre-existing renal impairment. Introduction: Gentamicin, a widely used aminoglycoside antibiotic, is an effective agent against various aerobic gram-negative bacteria. Its primary mechanism of action is the inhibition of bacterial protein synthesis by binding irreversibly to the 30S subunit of the bacterial ribosome, resulting in bactericidal effects. This antibiotic is generally administered via parenteral routes due to its poor gastrointestinal absorption, with common forms including intravenous, intramuscular, topical, and ophthalmic preparations. Gentamicin is effective in the treatment of various infections, including those of the bloodstream, urinary tract, gastrointestinal system, and soft tissues, particularly when the causative organisms are resistant to other antibiotics. In clinical settings, gentamicin's use should be supported by microbiological data whenever possible. In certain urgent or severe cases, such as septicemia or meningitis, empirical use of gentamicin may be considered based on local epidemiological trends, patient presentation, and the likelihood of encountering gentamicin-susceptible pathogens. The drug is especially effective against members of the Enterobacteriaceae family (e.g., Escherichia coli, Klebsiella pneumoniae), Pseudomonas aeruginosa, and select species from the genera Neisseria, Moraxella, and Haemophilus. While gentamicin remains a cornerstone for treating gram-negative infections, its clinical use is tempered by the potential for adverse effects, including nephrotoxicity and ototoxicity. Careful dosing and monitoring are therefore critical to maximizing efficacy while minimizing harm. Combination therapy with beta-lactam antibiotics can further enhance gentamicin's penetration into bacterial cells and is