Gentamicin

Pronunciation: JEN-ta-MYE-sin
Class: Antibiotic, Aminoglycoside, Ophthalmic

Trade Names

Garamycin
- Solution, ophthalmic 0.3%
- Ointment, ophthalmic 0.3%

Gentamicin
- Ointment, topical 0.1%
- Cream, topical 0.1%
- Injection, solution 10 mg/mL
- Injection, solution 40 mg/mL

Gentamicin Sulfate in Sodium Chloride 0.9%
- Injection, solution 0.6 mg/mL
- Injection, solution 0.8 mg/mL
- Injection, solution 0.9 mg/mL
- Injection, solution 1 mg/mL
- Injection, solution 1.2 mg/mL
- Injection, solution 1.4 mg/mL
- Injection, solution 1.6 mg/mL
- Injection, solution 2 mg/mL

Gentak
- Solution, ophthalmic 0.3%
- Ointment, ophthalmic 0.3%

Garamycin Topical Preparations (Canada)
ratio-Gentamicin (Canada)

Pharmacology

Inhibits production of bacterial protein, causing bacterial cell death.

Pharmacokinetics

Absorption

C max is 4 to 8 mcg/mL (IV). T max is 0.5 to 1 h (IM).

Distribution

Vd is 0.2 to 0.4 L/kg. Protein binding is 0% to 30%.

Metabolism

Little, if any, metabolic transformation occurs.

Elimination

Half-life is 2 h.

Special Populations

Renal Function Impairment

Cl is decreased in renal impairment.

Children

Excretion correlates with postnatal age and CrCl; with increasing postnatal age and concomitant increase in renal maturity, gentamicin is excreted more rapidly. Half-life increases with increasing age but is inversely related to weight. Peak serum levels increase with increasing age.

Indications and Usage

Injection

For the treatment of serious infections caused by susceptible strains of microorganisms.

Ophthalmic

For the topical treatment of ocular bacterial infections caused by susceptible strains of microorganisms.

Topical

For the treatment of primary skin infections (impetigo contagiosa, superficial folliculitis, ecthyma, furunculosis, sycosis barbae, pyoderma gangrenosum) and the treatment of secondary skin infections (infectious eczematoid dermatitis, pustular acne, pustular psoriasis, infected seborrheic dermatitis, infected contact dermatitis including poison ivy, infected excoriations, bacterial superinfections of fungal or viral infections).

Off-label uses

Pelvic inflammatory disease, surgical prophylaxis (injection).

Contraindications

Hypersensitivity to any component of the product or to other aminoglycosides.

Dosage and Administration

Serious Infections
Adults

IM/IV 3 mg/kg/day in 3 equal doses every 8 h. For life-threatening infections, up to 5 mg/kg/day may be administered in 3 or 4 equal doses. Reduce dosage to 3 mg/kg/day as soon as clinically indicated.

Children

IM/IV 6 to 7.5 mg/kg/day (2 to 2.5 mg/kg every 8 h).

Infants and Neonates

IM/IV 7.5 mg/kg/day (2.5 mg/kg every 8 h).

Premature or Full-term Neonates (1 wk of age or younger)

IM/IV 5 mg/kg/day (2.5 mg/kg every 12 h).

Superficial Skin Infections
Adults and Children 1 y or older

Topical Apply 3 to 4 times daily to the infected area.

Ocular Infections
Adults and Children 1 mo and older

Ophthalmic Apply a 0.5 inch ribbon of ointment in the affected eye 2 or 3 times daily or 1 to 2 drops of solution every 4 h; may increase to as much as 2 drops once every hour.

Renal function impairment

Dosage adjustment is required. May be adjusted by increasing the interval between administration of the usual doses or by decreasing the dosage. Refer to institution-specific pharmacy pharmacokinetic protocol.

General Advice

  • Injection
  • Base the dosage for obese patients on an estimate of the lean body mass.
  • Usual duration of treatment is 7 to 10 days. Longer courses may be required; monitoring of renal, auditory, and vestibular function is recommended in these cases.
  • Premixed, single-dose, flexible containers may be administered without further dilution.
  • Injection solution vials require dilution prior to IV administration. Dilute each dose with 50 to 200 mL of sodium chloride 0.9% or dextrose 5% in water; the volume of diluent should be less in infants and children.
  • Administer IV or IM. Infuse IV doses over 30 min to 2 h.
  • Do not mix with other medications.
  • Ophthalmic
  • For topical ophthalmic use only; not for ophthalmic injection.
  • Topical
  • For dermatologic use only; not for ophthalmic use.
  • The treatment area may be covered with a gauzed dressing.
  • Infected stasis ulcers have responded well to gentamicin under gelatin packing.
  • In impetigo contagiosa, the crusts should be removed before application of gentamicin.

Storage/Stability

Store between 68° and 77°F.

Drug Interactions

Drugs with nephrotoxic/neurotoxic potential (eg, amikacin, amphotericin, cephalosporins, cisplatin, colistin, enflurane, kanamycin, neomycin, paromomycin, polymyxin B, streptomycin, tobramycin, vancomycin)

May increase risk of nephrotoxicity and/or neurotoxicity. Avoid coadministration.

Loop diuretics (eg, ethacrynic acid, furosemide)

May increase risk of auditory toxicity. In addition, when administered IV, diuretics may enhance aminoglycoside toxicity by altering the antibiotic concentration in serum and tissue.

Neuromuscular blocking agents (eg, pancuronium, vecuronium), succinylcholine

Gentamicin may increase the neuromuscular-blocking effects of these agents. Prolonged respiratory depression and apnea may occur. If coadministration cannot be avoided, coadminister with caution. Carefully titrate the dosage of nondepolarizing muscle relaxants, and closely monitor neuromuscular function. Provide mechanical respiratory support as needed. Reversal of neuromuscular blockade by IV calcium salts and anticholinesterases is variable.

NSAIDs (eg, indomethacin, ketorolac)

Gentamicin concentrations may be elevated, increasing the risk of adverse reactions (eg, acute renal insufficiency). Avoid coadministration.

Adverse Reactions

Cardiovascular

Injection

Hypertension; hypotension.

CNS

Injection

Acute organic brain syndrome; confusion; convulsions; depression; dizziness; encephalopathy or peripheral neuropathy, including muscle twitching, myasthenia gravis–like syndrome, numbness, or skin tingling; headache; lethargy; pseudotumor cerebri; vertigo.

Ophthalmic

Hallucinations.

Dermatologic

Injection

Alopecia; generalized burning; itching; purpura; rash; urticaria.

Topical

Irritation, including erythema and pruritus; photosensitivity.

EENT

Injection

Hearing loss; roaring in the ears; tinnitus.

Ophthalmic

Bacterial and fungal corneal ulcers; conjunctival hyperemia; conjunctivitis; ocular burning and irritation.

GI

Injection

Increased salivation; nausea; splenomegaly; stomatitis; vomiting.

Genitourinary

Injection

Casts, cells, or protein in the urine; increased BUN, nonprotein nitrogen, or serum creatinine; oliguria.

Hematologic

Injection

Anemia; eosinophilia; granulocytopenia; leukopenia; thrombocytopenia; transient agranulocytosis.

Ophthalmic

Thrombocytopenic purpura.

Hepatic

Injection

Transient hepatomegaly.

Lab Tests

Injection

Decreased calcium, magnesium, potassium, reticulocyte counts, or sodium; increased ALT, AST, bilirubin, or LDH.

Local

Injection

Fat necrosis; local irritation; pain at injection site; subcutaneous atrophy.

Metabolic

Injection

Decreased appetite; weight loss.

Musculoskeletal

Injection

Joint pain.

Respiratory

Injection

Pulmonary fibrosis; respiratory depression.

Miscellaneous

Injection

Anaphylactoid reaction; fever; laryngeal edema.

Ophthalmic

Allergic reactions.

Precautions

Warnings

Injection

Patients treated with aminoglycosides should be under close clinical observation because of the potential toxicity associated with their use.

Nephrotoxicity

Gentamicin is potentially nephrotoxic; risk is greater in patients with impaired renal function and in those who receive high dosages or prolonged therapy.

Neurotoxicity

Neurotoxicity manifested by ototoxicity, both vestibular and auditory, can occur in patients treated with gentamicin, primarily in those with preexisting renal damage and in patients with healthy renal function treated with higher doses and/or for longer periods than recommended. Aminoglycoside-induced ototoxicity is usually irreversible. Other manifestations of neurotoxicity may include numbness, skin tingling, muscle twitching, and convulsions.

Monitoring

Renal and eighth cranial nerve functions should be closely monitored, especially in patients with known or suspected reduced renal function at onset of therapy and also in those whose renal function is initially healthy but who develop signs of renal dysfunction during therapy. Urine should be examined for decreased specific gravity, increased excretion of protein, and the presence of cells or casts. BUN, serum creatinine, or CrCl should be determined periodically. When feasible, it is recommended that serial audiograms be obtained in patients old enough to be tested, particularly high-risk patients. Evidence of ototoxicity (dizziness, vertigo, ataxia, tinnitus, roaring in the ears, or hearing loss) or nephrotoxicity requires dosage adjustment or discontinuation of the drug. As with the other aminoglycosides, on rare occasions, changes in renal and eighth cranial nerve function may not become manifest until soon after completion of therapy.

Serum concentrations of aminoglycosides should be monitored when feasible to ensure adequate levels and to avoid potentially toxic levels. When monitoring gentamicin peak concentrations, dosage should be adjusted so that prolonged levels above 12 mcg/mL are avoided. When monitoring gentamicin trough concentrations, dosage should be adjusted so that levels above 2 mcg/mL are avoided. Excessive peak or trough serum concentrations of aminoglycosides may increase the risk of renal and eighth cranial nerve toxicity. In the event of overdose or toxic reactions, hemodialysis may aid in the removal of gentamicin from the blood, especially if renal function is, or becomes, compromised. The rate of removal of gentamicin is considerably less by peritoneal dialysis than by hemodialysis.

Concomitant therapy

Concurrent and/or sequential systemic or topical use of other potentially neurotoxic and/or nephrotoxic drugs, such as amikacin, cephaloridine, cisplatin, colistin, kanamycin, neomycin, paromomycin, polymyxin B, streptomycin, tobramycin, vancomycin, and viomycin, should be avoided. Other factors that may increase patient risk of toxicity are advanced age and dehydration.

The concurrent use of gentamicin with potent diuretics, such as ethacrynic acid or furosemide, should be avoided because certain diuretics by themselves may cause ototoxicity. In addition, when administered IV, diuretics may enhance aminoglycoside toxicity by altering the antibiotic concentration in serum and tissue.

Pregnancy

Aminoglycosides can cause fetal harm when administered to pregnant women.


Monitor

Perform culture and susceptibility testing as indicated. Monitor patients for improvement in infection.


Pregnancy

Category D (injection); Category C (ophthalmic); Category undetermined (topical).

Lactation

Small amounts are excreted into the breast milk. The American Academy of Pediatrics classifies gentamicin as compatible with breast-feeding.

Children

Use gentamicin injection cautiously in premature infants and newborns because of renal immaturity. Gentamicin topical cream and ointment have been used successfully in children older than 1 y. Safety and effectiveness of gentamicin ophthalmic in neonates have not been established.

Elderly

Drug levels and renal function must be monitored closely during treatment with gentamicin injection.

Hypersensitivity

Cross-allergenicity among aminoglycosides has been demonstrated.

Renal Function

Dosage must be adjusted in patients with impaired renal function to ensure adequate, but not excessive, blood levels.

Superinfection

Treatment with antibiotics occasionally allows overgrowth of nonsusceptible organisms, including fungi.

Sulfite Sensitivity

Some products contain sulfites. Do not use if there is history of hypersensitivity.

Burn patients

Pharmacokinetics of gentamicin injection may be altered; serum levels must be closely monitored for dosing.

Corneal healing

Ophthalmic antibiotics may retard corneal healing.

Hydration

Ensure that patients are well hydrated during treatment with gentamicin injection.

Irritation

Discontinue use of gentamicin ophthalmic or topical if irritation or hypersensitivity develops.

Neuromuscular blockade

Potential curare-like effects may aggravate muscle weakness or cause neurotoxicity. Use with caution with anesthesia or muscle relaxants; in patients with hypocalcemia, hypokalemia, hypomagnesemia, and neuromuscular disorders (eg, myasthenia gravis, parkinsonism); and in newborns whose mothers received magnesium sulfate.

Overdosage

Symptoms

Nephrotoxicity, ototoxicity.

Patient Information

  • With parenteral administration, instruct patients to report any changes in urinary output (eg, decreased), dizziness, growth on the tongue, hearing (eg, ringing in ears, hearing loss), tingling or numbness in the hands and feet, and vaginal itch or discharge.
  • For topical application, instruct patients to cleanse the affected area of skin prior to application and to notify their health care provider if rash or irritation develops or if the condition worsens. Advise patients that the treated area may be covered with gauze if desired.
  • For ophthalmic use, instruct patients in the proper technique for instilling drops or ointment, emphasizing the importance of avoiding contact between the dispensing container and eyes, eyelids, or any surface. Inform patients that the drug may cause temporary blurring of vision or stinging after administration. Advise patients to notify their health care provider if stinging, itching, or burning increase or if irritation or pain persists. Discard the remaining ophthalmic preparation after completion of therapy.
  • Instruct patients to continue using medication for the prescribed time, even after signs and symptoms have been relieved, to prevent recurrence.
  • Caution patients to avoid exposure to sunlight and to use sunscreen or wear protective clothing to avoid a photosensitivity reaction.

Copyright © 2009 Wolters Kluwer Health.

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