Gentamicin

Pronunciation: (JEN-tuh-MY-sin)
Class: Antibiotic, Aminoglycoside, Ophthalmic

Trade Names

Gentamicin
- Ointment 0.3% (ophthalmic)
- Solution 0.3% (ophthalmic)
- Ointment 0.1% (topical)
- Cream 0.1% (topical)
- Injection 10 mg/mL (as sulfate)
- Injection 40 mg/mL (as sulfate)

Gentamicin Sulfate in sodium chloride 0.9%
- Injection 0.6 mg/mL (as base)
- Injection 0.8 mg/mL (as base)
- Injection 0.9 mg/mL (as base)
- Injection 1 mg/mL (as base)
- Injection 1.2 mg/mL (as base)
- Injection 1.4 mg/mL (as base)
- Injection 1.6 mg/mL (as base)
- Injection 2 mg/mL (as base)

Gentak
- Solution 0.3% (ophthalmic)
- Ointment 0.3% (ophthalmic)

Gentasol
- Solution 0.3% (ophthalmic)

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 1 h (IM). Oral absorption is poor.

Distribution

Vd is 0.2 to 0.4 L/kg. Protein binding is 0% to 10%. The half-life is 5 to 15 min. Distributed to extracellular ascitic, pericardial, pleural, synovial, lymphatic, and peritoneal fluids; body tissues; high concentrations in urine; low concentrations in breast milk, line spread function, and sputum. Crosses the placenta but does not cross the blood-brain barrier.

Elimination

Half-life is 2 h. Peritoneal dialysis is 25% removed in 48 to 72 h. Primary route is renal-glomerular filtration; 50% is removed during a 4 to 6 h hemodialysis period.

Special Populations

Renal Function Impairment

End-stage renal disease: half-life is 24 to 60 h.

Children

In infants younger than 1 wk old and less than 1,500 g, Vd is up to 0.68 L/kg; more than 1,500 g, Vd is up to 0.58 L/kg. Half-life is 5 to 8 h.

Indications and Usage

Short-term treatment of serious infections caused by susceptible strains of microorganisms, especially gram-negative bacteria; adjunct to systemic gentamicin in serious CNS infections (injection); treatment of superficial ocular infections (ophthalmic); treatment of primary (eg, impetigo contagiosa) and secondary (eg, infectious eczemafoid dermatitis) skin infections; skin cysts and superficial skin infections, infection prophylaxis, and aid to healing (topical).

Contraindications

Long-term therapy (injection); epithelial herpes simplex keratitis, vaccinia, varicella, mycobacterial infections, fungal diseases (ophthalmic); hypersensitivity to aminoglycosides.

Dosage and Administration

Adults

IM/IV 3 to 5 mg/kg/day in divided doses. For obese patients, base dose on estimate of lean body weight.

Children

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

Infants and Newborns

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

Premature or Term Newborns (younger than 1 wk of age)

IM/IV 5 mg/kg/day (2.5 mg/kg every 12 h) or 2.5 mg/kg every 18 h or 3 mg/kg every 24 h.

Prevention of Bacterial Endocarditis
Adults

IM/IV 1.5 mg/kg with ampicillin 30 min before procedure (max, 80 mg).

Children

IM/IV 2 mg/kg with ampicillin 30 min before procedure.

Superficial Skin Infections
Adults and Children

Topical Apply 3 to 4 times daily to infected area.

Ocular Infections
Adults and Children

Topical Apply 0.5-inch ribbon of ointment in each eye 2 or 3 times daily or 1 to 2 drops 4 to 6 times/day.

Storage/Stability

Store at 59° to 86°F.

Drug Interactions

Drugs with nephrotoxic potential (eg, amphotericin, cephalosporins, enflurane, methoxyflurane, vancomycin)

May increase risk of nephrotoxicity.

Loop diuretics

May increase risk of auditory toxicity.

Neuromuscular blocking agents

May enhance effects of these agents.

Polypeptide antibiotics

May increase risk of respiratory paralysis and renal function impairment.

Incompatibility

Do not mix beta-lactam antibiotics (eg, penicillins, especially ticarcillin and carbenicillin, cephalosporins) in IV solutions.

Laboratory Test Interactions

None well documented.

Adverse Reactions

CNS

Headache; dizziness; vertigo; encephalopathy; confusion; fever; lethargy; convulsions; muscle weakness and twitching; peripheral neuropathy; acute organic brain syndrome; depression; pseudotumor cerebri; increased CSF protein; arachnoiditis or burning at injection site after intrathecal administration.

Dermatologic

Rash; urticaria; itching; anaphylaxis; photosensitivity (topical).

EENT

Blurred vision; tinnitus; hearing loss; mydriasis and conjunctival paresthesia (ophthalmic).

GI

Nausea; vomiting.

Genitourinary

Oliguria; proteinuria; increased serum creatinine and BUN; casts; Fanconi-like syndrome.

Hematologic

Anemia; eosinophilia; leukopenia; thrombocytopenia; granulocytopenia.

Hepatic

Elevated LFT results.

Respiratory

Apnea; pulmonary fibrosis.

Miscellaneous

Pain and irritation at injection site; splenomegaly; hypomagnesemia; hyponatremia; hypocalcemia; hypokalemia.

Precautions

Warnings Injection Neurotoxicity Manifests as both auditory and vestibular ototoxicity, and primarily occurs in patients with pre-existing renal damage or in healthy renal function with prolonged therapy. Partial or total irreversible deafness may continue to develop after drug is stopped. Other features of neurotoxicity include paresthesias, twitching, and seizures. Nephrotoxicity Usually reversible. Closely monitor renal and eighth nerve function in patients with suspected renal function impairment. Monitor peak and trough concentrations. Dosage adjustments required in renal function impairment.

Pregnancy

Category D (injection). Category C (ophthalmic and topical).

Lactation

Small amounts excreted into the breastmilk.

Children

Use cautiously in premature infants and newborns because of renal immaturity.

Elderly

Drug levels and renal function must be monitored closely.

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 may be altered; serum levels must be closely monitored for dosing.

Hypomagnesemia

Occurs often, especially in those with restricted diets or poor nutrition.

Neuromuscular blockade

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

Overdosage

Symptoms

Nephrotoxicity, ototoxicity.

Patient Information

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

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