Gentamicin – Warnings


Gentamicin is an antibacterial prescription medicine approved by the U.S. Food and Drug Administration (FDA) for the treatment of several infections caused by certain types of bacteria, such as meningitis, infection of the blood, and serious urinary tract infections.

Gentamicin is a bactericidal aminoglycoside that was discovered and isolated from Micromonospora purpurea in 1963. It is one of the most frequently prescribed aminoglycosides due to its spectrum of activity, low cost, and availability. Gentamicin is effective against both gram-positive and gram-negative organisms but is particularly useful for the treatment of severe gram-negative infections including those caused by Pseudomonas aeruginosa. There is the added benefit of synergy when gentamicin is co-administered with other antibacterials such as beta-lactams. This synergistic activity is not only important for the treatment of complex infections, but can also contribute to dose optimization and reduced adverse effects.

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Properties and Characteristics of Gentamicin

Drug class Aminoglycosides Antibiotics
Brand Names Garamycin, Cidomycin
Synonyms Gentamicin, Garamycin, Gentacycol, Gentavet, Uromycine, Gentamicina
Molecular Formula C21H43N5O7
Molecular Weight 477.6 g/mol
IUPAC Names 2-[4,6-diamino-3-[3-amino-6-[1-(methylamino)ethyl]oxan-2-yl]oxy-2-hydroxycyclohexyl]oxy-5-methyl-4-(methylamino)oxane-3,5-diol
Structural formula of main components Gentamicin Structure.png
Pure active ingredient Gentamicin
Appearance White to buff colored, odorless, hygroscopic powder
Melting point   105 °C
Solubility 12.6 mg/mL
Excretion Excreted primarily by the kidneys
Available as Topical cream, Solution / drops, Intramuscular injection, Intravenous injection
Storage Store at 20°C to 25°C (68°F to 77°F).
Prescription Prescription is required

Uses of Gentamicin

What is it prescribed for?


Bacteremia is the presence of bacteria in the blood. Bacteria can sometimes enter your bloodstream from dental or medical procedures, or from infections. If this condition left untreated it can lead to septicemia which is an infection of the blood caused by bacteria. Gentamicin is used for the treatment of bacteremia.

Intra-abdominal Infection

Intra-abdominal infection (IAI) describes a number of infections such as peritonitis (swelling of the peritoneum-lining of the abdominal wall), pancreatitis (swelling of the pancreas- an organ located behind the lower part of the stomach), diverticulitis (swelling of diverticula- one or more small pouches in the intestine), cholecystitis (swelling of the gallbladder-a small digestive organ that sits just under the liver), and cholangitis (swelling of the bile duct system). Gentamicin is used to treat infections occurring within the abdomen caused by bacteria.

Bacterial Meningitis

Bacterial meningitis is an infection of the meninges, the protective layer that surrounds the brain and spinal cord. It starts when bacteria get into your bloodstream and travel to your brain and spinal cord. Gentamicin is used to treat bacterial meningitis.

Bone and joint infections

Bone and joint infections occur in the bones and joints. Osteomyelitis is an infection of the bone and septic arthritis is an infection in a joint. These infections can occur due to a bone/joint injury or through blood by which bacteria, virus, or fungi invade a bone/joint. Gentamicin is used for the treatment of osteomyelitis and septic arthritis caused by bacteria.

Skin and soft tissue infections

Skin and soft tissue infections occur when the bacteria invade the skin and its supporting structures. Gentamicin is used to treat all skin infections including abscess caused by bacteria.

Urinary tract infections

An infection in any part of your urinary system- the kidneys, bladder, ureters, or urethra is called urinary tract infections (UTIs). UTIs are the most common infections in humans and woman are at greater risk of getting this infection. UTI’s can occur as complicated or uncomplicated urinary tract infections.

Complicated UTI’s are caused by multidrug-resistant bacteria (the bacteria may become non-responsive to more than one antibiotic) and can occur due to structural and functional abnormalities of the urinary tract. Uncomplicated urinary tract infection is an infection of the urinary tract in a healthy individual with a normal and functional urinary tract and no known reasons to develop a UTI. Gentamicin is used to treat complicated and uncomplicated urinary tract infections caused by bacteria.

Bacterial skin infections

Bacteria enters into the skin through cuts or scratches causing bacterial skin infections such as cellulitis, impetigo, folliculitis, etc. Gentamicin topical (for use on the skin) is used to treat bacterial skin infections that are characterised by redness, warmth, swelling, itching and irritation of the skin.

Bacterial eye infections

Gentamicin eye drops are used to treat bacterial eye infections mainly the infection affecting the conjunctiva (a clear tissue covering the white part of your eye and lines the inside of the eyelid) called conjunctivitis or pink eye. It is also used to treat keratitis, a condition of swelling of the cornea (a transparent layer of tissue at the front of the eye) caused by bacteria. Gentamicin eye drops uses are proven to be safe and effective in treating eye infections.

Bacterial Ear Infections

Gentamicin ear drops are used to treat bacterial ear infections mainly Otitis Externa or Swimmer’s ear, an infection in the ear canal, which connects the outside of the ear to the eardrum.

Community-Acquired Pneumonia

Community-acquired pneumonia (CAP) refers to pneumonia (lung infection) that is acquired outside the hospital. CAP can be bacterial or viral. Gentamicin is used to treat CAP caused by bacteria like Mycoplasma pneumonia, Streptococcus pneumonia, Haemophilus influenzae, etc.

What are the side effects of Gentamicin (Garamycin)?

Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Call your doctor at once if you have:

  • Hearing loss, or a roaring sound in your ears;
  • Severe or ongoing dizziness;
  • Weak or shallow breathing;
  • Numbness or tingly feeling;
  • Twitching, muscle tightness or contraction;
  • Seizure (convulsions);
  • Severe stomach pain, diarrhea that is watery or bloody;
  • Fever, blisters or ulcers in your mouth, red or swollen gums, trouble swallowing;
  • Kidney problems–little or no urinating; painful or difficult urination; swelling in your feet or ankles; feeling tired or short of breath;
  • Signs of an electrolyte imbalance–confusion, weakness, bone pain, increased urination; or
  • Increased pressure inside the skull–severe headaches, ringing in your ears, dizziness, nausea, vision problems, pain behind your eyes.

Side effects may be more likely in older adults.

Common side effects may include:

  • Vision problems;
  • Nausea, vomiting, loss of appetite, weight loss;
  • A light-headed feeling, like you might pass out;
  • Itching or rash;
  • Pain where the medicine was injected;
  • Headache, mood changes; or
  • Joint pain.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects.

Mechanism of action

There are 3 key phases of aminoglycoside entry into cells. The first “ionic binding phase” occurs when polycationic aminoglycosides bind electrostatically to negatively charged components of bacterial cell membranes including with lipopolysaccharides and phospholipids within the outer membrane of Gram-negative bacteria and to teichoic acids and phospholipids within the cell membrane of Gram-positive bacteria. This binding results in displacement of divalent cations and increased membrane permeability, allowing for aminoglycoside entry. The second “energy-dependent phase I” of aminoglycoside entry into the cytoplasm relies on the proton-motive force and allows a limited amount of aminoglycoside access to its primary intracellular target – the bacterial 30S ribosome. This ultimately results in the mistranslation of proteins and disruption of the cytoplasmic membrane. Finally, in the “energy-dependent phase II” stage, concentration-dependent bacterial killing is observed. Aminoglycoside rapidly accumulates in the cell due to the damaged cytoplasmic membrane, and protein mistranslation and synthesis inhibition is amplified. The necessity of oxygen-dependent active transport explains why aminoglycosides are ineffective against anaerobic bacteria. Hence, aminoglycosides have both immediate bactericidal effects through membrane disruption and delayed bactericidal effects through impaired protein synthesis; observed experimental data and mathematical modelling support this two-mechanism model. Inhibition of protein synthesis is a key component of aminoglycoside efficacy. Structural and cell biological studies suggest that aminoglycosides bind to the 16S rRNA in helix 44 (h44), near the A site of the 30S ribosomal subunit, altering interactions between h44 and h45. This binding also displaces two important residues, A1492 and A1493, from h44, mimicking normal conformational changes that occur with successful codon-anticodon pairing in the A site. Overall, aminoglycoside binding has several negative effects including inhibition of translation, initiation, elongation, and ribosome recycling. Recent evidence suggests that the latter effect is due to a cryptic second binding site situated in h69 of the 23S rRNA of the 50S ribosomal subunit. Also, by stabilizing a conformation that mimics correct codon-anticodon pairing, aminoglycosides promote error-prone translation. Mistranslated proteins can incorporate into the cell membrane, inducing the damage discussed above.

Drug Interactions with Gentamicin

Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are receiving this medicine, it is especially important that your healthcare professional know if you are taking any of the medicines listed below. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.

Using this medicine with any of the following medicines is not recommended. Your doctor may decide not to treat you with this medication or change some of the other medicines you take.

  • Ataluren

Using this medicine with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.

  • Agalsidase Alfa
  • Alcuronium
  • Aspirin
  • Cholera Vaccine, Live
  • Cidofovir
  • Cisatracurium
  • Decamethonium
  • Digoxin
  • Doxacurium
  • Ethacrynic Acid
  • Fazadinium

Using this medicine with any of the following medicines may cause an increased risk of certain side effects, but using both drugs may be the best treatment for you. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.

  • Indomethacin
  • Methoxyflurane
  • Polygeline

Other Interactions

Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Using alcohol or tobacco with certain medicines may also cause interactions to occur. Discuss with your healthcare professional the use of your medicine with food, alcohol, or tobacco.

Other Medical Problems

The presence of other medical problems may affect the use of this medicine. Make sure you tell your doctor if you have any other medical problems, especially:

  • Asthma or
  • Sulfite allergy, history of—This medicine contains sodium metabisulfite which may cause an allergic reaction in patients with these conditions.
  • Hypocalcemia (low calcium in the blood) or
  • Hypokalemia (low potassium in the blood) or
  • Hypomagnesemia (low magnesium in the blood)—Should be corrected before receiving this medicine. If these conditions are not corrected, this medicine may increase risk for more serious side effects.
  • Kidney disease—Use with caution. The effects may be increased because of slower removal of this medicine from the body.
  • Kidney disease, severe or
  • Muscle problems or
  • Myasthenia gravis (severe muscle weakness) or
  • Nerve problems—Use with caution. May make these conditions worse.

What is the dosage for gentamicin?

The dose of gentamicin is usually based on body weight. The total daily dose and duration of treatment depend on the condition or infection being treated. Dose adjustment is necessary for patients who have impaired kidney function. Doses are adjusted to target peak and trough levels.

  • Usual dosage ranges for IM or IV:
  • Conventional dosing: Administer 1 to 2.5 mg/kg/dose every 8-12 hours.
  • Once daily dosing: Administer 4 to 7 mg/kg/day.


Injection: Since gentamicin injection is administered in the hospital or clinical setting by a qualified healthcare professional, the likelihood of an overdose is very low. However, emergency medical treatment will be initiated by the doctor if an overdose is suspected.

Topical forms: Seek emergency medical attention in case of an overdose with gentamicin eye drops.

What are warnings and precautions for Gentamicin?


  • Patients with dementia-related psychosis who are treated with antipsychotic drugs are at increased risk for death, as shown in short-term controlled trials; deaths in these trials appeared to be either cardiovascular (e.g., heart failure, sudden death) or infectious (e.g., pneumonia) in nature.
  • This drug is not approved for the treatment of patients with dementia-related psychosis.
  • This medication contains gentamicin. Do not take Modecate, Modecate Concentrate, Moditen, Prolixin, or RhoGentamicin if you are allergic to gentamicin or any ingredients contained in this drug.
  • Keep out of reach of children. In case of overdose, get medical help or contact a Poison Control Center immediately.

Gentamicin Pregnancy Warnings

Animal studies have failed to reveal evidence of fetotoxicity, fetal harm, or impaired fertility with this drug. There are reports of total irreversible, bilateral congenital deafness in children whose mothers’ used streptomycin during pregnancy. Evidence of (probably reversible) damage to immature nephrons of the fetal kidney associated with use, and eighth cranial nerve damage associated with aminoglycoside exposure in utero have been reported. There are no controlled data in human pregnancy.

Gentamicin Breastfeeding Warnings

Use is not recommended and a decision should be made to discontinue breastfeeding or discontinue the drug, taking into account the importance of the drug to the mother. It is excreted into human milk.

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