Interactions with supplements
Alpha-Lipoic Acid
Look Up > Drugs > Gentamicin
U.S. Brand Names
Generic Available
Pharmacological Index
Pregnancy Risk Factor
Adverse Reactions
Drug Interactions
Mechanism of Action
Usual Dosage
Dietary Considerations
Monitoring Parameters
Reference Range
Test Interactions
Mental Health: Effects on Mental Status
Mental Health: Effects on Psychiatric Treatment
Dental Health: Local Anesthetic/Vasoconstrictor Precautions
Dental Health: Effects on Dental Treatment
Patient Information
Nursing Implications
Dosage Forms

(jen ta MYE sin)

U.S. Brand Names
Garamycin® Injection; Garamycin® Ophthalmic; Garamycin® Topical; Genoptic® Ophthalmic; Genoptic® S.O.P. Ophthalmic; Gentacidin® Ophthalmic; Gentak® Ophthalmic; G-myticin® Topical; Jenamicin® Injection

Generic Available


Gentamicin Sulfate

Pharmacological Index

Antibiotic, Aminoglycoside; Antibiotic, Ophthalmic; Antibiotic, Topical


Treatment of susceptible bacterial infections, normally gram-negative organisms including Pseudomonas, Proteus, Serratia, and gram-positive Staphylococcus; treatment of bone infections, respiratory tract infections, skin and soft tissue infections, as well as abdominal and urinary tract infections, endocarditis, and septicemia; used topically to treat superficial infections of the skin or ophthalmic infections caused by susceptible bacteria; prevention of bacterial endocarditis prior to dental or surgical procedures

Pregnancy Risk Factor



Hypersensitivity to gentamicin or other aminoglycosides


Not intended for long-term therapy due to toxic hazards associated with extended administration; pre-existing renal insufficiency, vestibular or cochlear impairment, myasthenia gravis, hypocalcemia, conditions which depress neuromuscular transmission

Adverse Reactions


Central nervous system: Neurotoxicity (vertigo, ataxia)

Neuromuscular & skeletal: Gait instability

Otic: Ototoxicity (auditory), ototoxicity (vestibular)

Renal: Nephrotoxicity, decreased creatinine clearance

1% to 10%:

Cardiovascular: Edema

Dermatologic: Skin itching, reddening of skin, rash

<1%: Drowsiness, headache, pseudomotor cerebri, photosensitivity, erythema, anorexia, nausea, vomiting, weight loss, increased salivation, enterocolitis, granulocytopenia, agranulocytosis, thrombocytopenia, elevated LFTs, burning, stinging, tremors, muscle cramps, weakness, dyspnea


Symptoms of overdose include ototoxicity, nephrotoxicity, and neuromuscular toxicity; serum level monitoring is recommended

The treatment of choice, following a single acute overdose, appears to be the maintenance of good urine output of at least 3 mL/kg/hour. Dialysis is of questionable value in the enhancement of aminoglycoside elimination. If required, hemodialysis is preferred over peritoneal dialysis in patients with normal renal function. Careful hydration may be all that is required to promote diuresis and therefore the enhancement of the drug's elimination. Chelation with penicillins is experimental.

Drug Interactions

Increased toxicity:

Neuromuscular blocking agents may increase neuromuscular blockade


Gentamicin is a colorless to slightly yellow solution which should be stored between 2°C to 30°C, but refrigeration is not recommended

I.V. infusion solutions mixed in NS or D5W solution are stable for 24 hours at room temperature and refrigeration

Premixed bag: Manufacturer expiration date

Out of overwrap stability: 30 days

Mechanism of Action

Interferes with bacterial protein synthesis by binding to 30S and 50S ribosomal subunits resulting in a defective bacterial cell membrane


Absorption: Oral: Not absorbed

Distribution: Crosses the placenta

Vd: Increased by edema, ascites, fluid overload; decreased in patients with dehydration

Neonates: 0.4-0.6 L/kg

Children: 0.3-0.35 L/kg

Adults: 0.2-0.3 L/kg

Relative diffusion of antimicrobial agents from blood into cerebrospinal fluid (CSF): Minimal even with inflammation

Ratio of CSF to blood level (%): Normal meninges: Nil; Inflamed meninges: 10-30

Protein binding: <30%


Infants: <1 week: 3-11.5 hours; 1 week to 6 months: 3-3.5 hours

Adults: 1.5-3 hours; end-stage renal disease: 36-70 hours

Time to peak serum concentration: I.M.: Within 30-90 minutes; I.V.: 30 minutes after a 30-minute infusion

Elimination: Clearance is directly related to renal function, eliminated almost completely by glomerular filtration of unchanged drug with excretion into the urine

Usual Dosage

Individualization is critical because of the low therapeutic index

In morbid obesity, dosage requirement may best be estimated using a dosing weight of IBW + 0.4 (TBW - IBW)

Initial and periodic peak and trough plasma drug levels should be determined, particularly in critically ill patients with serious infections or in disease states known to significantly alter aminoglycoside pharmacokinetics (eg, cystic fibrosis, burns, or major surgery)

Newborns: Intrathecal: 1 mg every day

Infants >3 months: Intrathecal: 1-2 mg/day

Infants and Children <5 years: I.M., I.V.: 2.5 mg/kg/dose every 8 hours*

Cystic fibrosis: 2.5 mg/kg/dose every 6 hours

Children >5 years: I.M., I.V.: 1.5-2.5 mg/kg/dose every 8 hours*

Prevention of bacterial endocarditis: Dental, oral, upper respiratory procedures, GI/GU procedures: 2 mg/kg with ampicillin (50 mg/kg) 30 minutes prior to procedure

*Some patients may require larger or more frequent doses (eg, every 6 hours) if serum levels document the need (ie, cystic fibrosis or febrile granulocytopenic patients)

Adults: I.M., I.V.:

Severe life-threatening infections: 2-2.5 mg/kg/dose

Urinary tract infections: 1.5 mg/kg/dose

Synergy (for gram-positive infections): 1 mg/kg/dose

Prevention of bacterial endocarditis:

Dental, oral, or upper respiratory procedures: 1.5 mg/kg not to exceed 80 mg with ampicillin (1-2 g) 30 minutes prior to procedure

GI/GU surgery: 1.5 mg/kg not to exceed 80 mg with ampicillin 2 g 30 minutes prior to procedure

Children and Adults:

Intrathecal: 4-8 mg/day


Ointment: Instill 1/2 " (1.25 cm) 2-3 times/day to every 3-4 hours

Solution: Instill 1-2 drops every 2-4 hours, up to 2 drops every hour for severe infections

Topical: Apply 3-4 times/day to affected area

Some clinicians suggest a daily dose of 4-7 mg/kg for all patients with normal renal function. This dose is at least as efficacious with similar, if not less, toxicity than conventional dosing.

Dosing interval in renal impairment:

Clcr greater than or equal to 60 mL/minute: Administer every 8 hours

Clcr 40-60 mL/minute: Administer every 12 hours

Clcr 20-40 mL/minute: Administer every 24 hours

Clcr <20 mL/minute: Loading dose, then monitor levels

Hemodialysis: Dialyzable; removal by hemodialysis: 30% removal of aminoglycosides occurs during 4 hours of HD; administer dose after dialysis and follow levels

Removal by continuous ambulatory peritoneal dialysis (CAPD):

Administration via CAPD fluid:

Gram-negative infection: 4-8 mg/L (4-8 mcg/mL) of CAPD fluid

Gram-positive infection (ie, synergy): 3-4 mg/L (3-4 mcg/mL) of CAPD fluid

Administration via I.V., I.M. route during CAPD: Dose as for Clcr <10 mL/minute and follow levels

Removal via continuous arteriovenous or venovenous hemofiltration (CAVH/CAVHD): Dose as for Clcr 10-40 mL/minute and follow levels

Dosing adjustment/comments in hepatic disease: Monitor plasma concentrations

Dietary Considerations

Calcium, magnesium, potassium: Renal wasting may cause hypocalcemia, hypomagnesemia, and/or hypokalemia

Monitoring Parameters

Urinalysis, urine output, BUN, serum creatinine; hearing should be tested before, during, and after treatment; particularly in those at risk for ototoxicity or who will be receiving prolonged therapy (>2 weeks)

Reference Range

Timing of serum samples: Draw peak 30 minutes after 30-minute infusion has been completed or 1 hour after I.M. injection; draw trough immediately before next dose

Sample size: 0.5-2 mL blood (red top tube) or 0.1-1 mL serum (separated)

Therapeutic levels:


Serious infections: 6-8 mg/mL (12-17 mmol/L)

Life-threatening infections: 8-10 mg/mL (17-21 mmol/L)

Urinary tract infections: 4-6 mg/mL

Synergy against gram-positive organisms: 3-5 mg/mL


Serious infections: 0.5-1 mg/mL

Life-threatening infections: 1-2 mg/mL

Obtain drug levels after the third dose unless renal dysfunction/toxicity suspected

Test Interactions

Penicillin may decrease aminoglycoside serum concentrations in vitro

Mental Health: Effects on Mental Status

Dizziness is common; may cause drowsiness

Mental Health: Effects on Psychiatric Treatment

May rarely cause agranulocytosis; use caution with clozapine and carbamazepine

Dental Health: Local Anesthetic/Vasoconstrictor Precautions

No information available to require special precautions

Dental Health: Effects on Dental Treatment

Increased salivation has been reported

Patient Information

Take exactly as directed and when prescribed. Drink adequate amounts of water (2-3 L/day of fluids unless instructed to restrict fluid intake). You may experience headaches, ringing in ears, dizziness, blurred vision (use caution when driving or engaging in tasks requiring alertness until response to drug is known); GI upset, loss of appetite (small frequent meals and frequent mouth care may help); photosensitivity (use sunscreen wear protective clothing and eyewear, and avoid direct sunlight). Report severe headache, changes in hearing acuity or ringing in ears, changes in urine pattern, difficulty breathing, rash, fever, unhealed sores, sores in mouth, vaginal drainage, muscle or bone pain, change in gait, or worsening of condition. Pregnancy/breast-feeding precautions: Inform prescriber if you are or intend to be pregnant. Consult prescriber if breast-feeding.

Topical: Apply thin film of ointment to affected area as often as recommended. May apply porous dressing. Report persistent burning, swelling, itching, worsening of condition, or lack of response to therapy.

Nursing Implications

Slower absorption and lower peak concentrations probably due to poor circulation in the atrophic muscle, may occur following I.M. injection in paralyzed patients (suggest I.V. route); aminoglycoside levels measured in blood taken from Silastic® central catheters can sometimes give falsely high readings (draw via separate lumen or peripheral site if possible, otherwise flush very well). Monitor serum creatinine and urine output; obtain drug levels after the third dose unless otherwise directed (eg, suspected toxicity or renal dysfunction). Peak levels are drawn 30 minutes after the end of a 30-minute infusion or 60 minutes following I.M. injection; trough levels are drawn within 30 minutes before the next dose; administer other antibiotic drugs at least 1 hour before or after gentamicin. Hearing should be tested before, during, and after treatment in patients at risk for ototoxicity.

Dosage Forms

Cream, topical, as sulfate (Garamycin®, G-myticin®): 0.1% (15 g)

Infusion, in D5W, as sulfate: 60 mg, 80 mg, 100 mg

Infusion, in NS, as sulfate: 40 mg, 60 mg, 80 mg, 90 mg, 100 mg, 120 mg

Injection, as sulfate: 40 mg/mL (1 mL, 1.5 mL, 2 mL)

Pediatric, as sulfate: 10 mg/mL (2 mL)

Intrathecal, preservative free, as sulfate (Garamycin®): 2 mg/mL (2 mL)

Ointment, as sulfate:

Ophthalmic: 0.3% [3 mg/g] (3.5 g)

Garamycin®, Genoptic® S.O.P., Gentacidin®, Gentak®: 0.3% [3 mg/g] (3.5 g)

Topical, as sulfate (Garamycin®, G-myticin®): 0.1% (15 g)

Solution, ophthalmic, as sulfate: 0.3% (5 mL, 15 mL)

Garamycin®, Genoptic®, Gentacidin®, Gentak®: 0.3% (1 mL, 5 mL, 15 mL)


Begg EJ and Barclay ML, "Aminoglycosides - 50 Years On," Br J Clin Pharmacol, 1995, 39(6):597-603.

Bhatt-Mehta V, Johnson CE and Schumacher RE, "Gentamicin Pharmacokinetics in Term Neonates Receiving Extracorporeal Membrane Oxygenation," Pharmacotherapy, 1992, 12(1):28-32.

Council on Dental Therapeutics, American Heart Association, "Preventing Bacterial Endocarditis," J Am Dent Assoc, 1991, 122(2):87-92.

Cunha BA, "Aminoglycosides: Current Role in Antimicrobial Therapy," Pharmacotherapy, 1988, 8(6):334-50.

Dajani AS, Bisno AL, Chung KJ, et al, "Prevention of Bacterial Endocarditis, Recommendations by the American Heart Association," JAMA, 1990, 264(22):2919-22.

Edson RS and Terrell CL, "The Aminoglycosides," Mayo Clin Proc, 1999, 74(5):519-28.

Fuquay D, Koup J, and Smith AL, "Management of Neonatal Gentamicin Overdosage," J Pediatr, 1981, 99(3):473-6.

Gilbert DN, "Once-Daily Aminoglycoside Therapy," Antimicrob Agents Chemother, 1991, 35(3):399-405.

Hustinx WN, and Hoepelman IM, "Aminoglycoside Dosage Regimens. Is Once a Day Enough?" Clin Pharmacokinet, 1993, 25(6):427-32.

Iseman MD, "Treatment of Multidrug-Resistant Tuberculosis," N Engl J Med, 1993, 329(11):784-91.

Lortholary O, Tod M, Cohen Y, et al, "Aminoglycosides," Med Clin North Am, 1995, 79(4):761-87.

Lucena MI, Andrade RJ, Cabello MR, et al, "Aminoglycoside-Associated Nephrotoxicity in Extrahepatic Obstructive Jaundice," J Hepatol, 1995, 22(2):189-96.

Matz GJ, "Aminoglycoside Ototoxicity," Am J Otolaryngol, 1986, 7(2):117-9.

Matzke GR, Jameson JJ, and Halstenson CE, "Gentamicin Disposition in Young and Elderly Patients With Various Degrees of Renal Function," J Clin Pharmacol, 1987, 27(3):216-20.

McCormack JP and Jewesson PJ, "A Critical Re-Evaluation of the "Therapeutic Range" of Aminoglycosides," Clin Infect Dis, 1992, 14(1):320-39.

Nicolau DP, Freeman CD, Belliveau PP, et al, "Experience With a Once-Daily Aminoglycoside Program Administered to 2184 Adult Patients," Antimicrob Agents Chemother, 1995, 39(3):650-5.

O'Brien RK and Sparling TG, "Gentamicin and Fludarabine Ototoxicity," Ann Pharmacother, 1995, 29(2):200-1.

Preston SL and Briceland LL, "Single Daily Dosing of Aminoglycosides," Pharmacotherapy, 1995, 15(3):297-316.

Reimche LD, Rooney, ME, Hindmarsh KW, et al, "An Evaluation of Gentamicin Dosing According to Renal Function in Neonates With Suspected Sepsis," Am J Perinatol, 1987, 4(3):262-5.

Schentag JJ, Simons GW, Schultz RW, et al, "Complexation Versus Hemodialysis to Reduce Elevated Aminoglycoside Serum Concentrations," Pharmacotherapy, 1984, 4(6):374-80.

Shevchuk YM and Taylor DM, "Aminoglycoside Volume of Distribution in Pediatric Patients," DICP, 1990, 24(3):273-6.

Terrell CL, "Antifungal Agents. Part II. The Azoles," Mayo Clin Proc, 1999, 74(1):78-100.

Wynn RL, "Gentamicin for Prophylaxis of Bacterial Endocarditis: A Review for the Dentist," Oral Surg Oral Med Oral Pathol, 1985, 60(2):159-65.

Zaske DE, Irvine P, Strand LM, et al, "Wide Interpatient Variations in Gentamicin Dose Requirements for Geriatric Patients," JAMA, 1982, 248(23):3122-6.

Copyright © 1978-2000 Lexi-Comp Inc. All Rights Reserved