GENTAMICIN SULFATE

GENTAMICIN SULFATE
(jen-ta-mye'sin)
Garamycin Ophthalmic, Genoptic
Classifications: aminoglycoside antibiotic;
Therapeutic: antibiotic

Pregnancy Category: D

Availability

10 mg/mL, 40 mg/mL; 0.1% ointment, cream; 3 mg/mL ophthalmic solution; 3 mg/g ophthalmic ointment

Action

Broad-spectrum aminoglycoside antibiotic that binds irreversibly to 30S subunit of bacterial ribosomes, blocking a vital step in protein synthesis, and attachment of RNA molecules to bacterial ribosomes resulting in cell death.

Therapeutic Effect

Active against a wide variety of aerobic gram-negative but not anaerobic gram-negative bacteria. Also effective against certain gram-positive organisms, particularly penicillin-sensitive and some methicillin-resistant strains of Staphylococcus aureus (MRSA).

Uses

Parenteral use restricted to treatment of serious infections of GI, respiratory, and urinary tracts, CNS, bone, skin, and soft tissue (including burns) when other less toxic antimicrobial agents are ineffective or are contraindicated. Has been used in combination with other antibiotics. Also used topically for primary and secondary skin infections and for superficial infections of external eye and its adnexa.

Unlabeled Uses

Prophylaxis of bacterial endocarditis in patients undergoing operative procedures or instrumentation.

Contraindications

History of hypersensitivity to or toxic reaction with any aminoglycoside antibiotic; pregnancy (category D).

Cautious Use

Impaired renal function; history of eighth cranial (acoustic) nerve impairment; preexisting vertigo or dizziness or tinnitus; dehydration, fever; renal impairment, dehydration; Fabry disease; use in older adults, premature infants, neonates, and infants; obesity, neuromuscular disorders: myasthenia gravis, parkinsonian syndrome; hypocalcemia, heart failure, topical applications to widespread areas.

Route & Dosage

Moderate to Severe Infection
Adult: IV/IM 1–2 mg/kg loading dose followed by 3–5 mg/kg/d in 3 divided doses  Intrathecal 4–8 mg preservative free q.d.  Topical 1–2 drops of solution in eye q4h up to 2 drops q1h or small amount of ointment b.i.d. or t.i.d.
Child: IV/IM 6–7.5 mg/kg/d in 3 divided doses  Intrathecal >3 mo, 1–2 mg preservative free q.d.
Neonate: IV/IM 2.5 mg/kg/d

Prophylaxis of Bacterial Endocarditis
Adult: IV/IM 1.5 mg/kg 30 min before procedure, may repeat in 8 h
Child (<27 kg): IV/IM 2 mg/kg 30 min before procedure, may repeat in 8 h

Obesity
Dose based on IBW, in morbid obesity use IBW +0.4 (TBW–IBW).

Renal Impairment
Reduce dose or extend dosing interval.

Administration

Ophthalmic
  • Apply pressure to inner canthus for 1 min immediately after instillation of drops.
  • Have patient keep eyes closed for 1–2 min after administration of ophthalmic ointment to assure medication contact. Caution patient that vision will be blurred for a few minutes.
Topical
  • Wash affected area with mild soap and water, rinse, and dry thoroughly. Gently apply small amount of medication to lesions; cover with sterile gauze.
  • Do not apply topical preparations, particularly cream, to large denuded body surfaces because systemic absorption and toxicity are possible.
Intramuscular
  • Give deep into a large muscle.
  • Do not use solutions that are discolored or that contain particulate matter; drug for IV or IM is clear and colorless or slightly yellow.
Intrathecal
  • Note: Intrathecal formulation is a clear and colorless solution.
  • Use promptly after opening; contains no preservatives and any unused portion should be discarded.
Intravenous

PREPARE: Intermittent: Dilute a single dose with 50–200 mL of D5W or NS. For pediatric patients, amount of infusion fluid may be proportionately smaller depending on patient's needs but should be sufficient to be infused over the same time period as for adults.  

ADMINISTER: Intermittent: Give over 30 min–2 h.  

INCOMPATIBILITIES Solution/additive: Fat emulsion, TPN, amphotericin B, ampicillin, carbenicillin, cephalosporins, cytarabine, heparin, ticarcillin. Y-site: Allopurinol, amphotericin B cholesteryl, azithromycin, furosemide, heparin, hetastarch, idarubicin, indomethacin, iodipamide, propofol, warfarin.

  • Store all gentamicin solutions between 2°–30° C (36°–86° F) unless otherwise directed by manufacturer.

Adverse Effects (≥1%)

Special Senses: Ototoxicity (vestibular disturbances, impaired hearing), optic neuritis. CNS: Neuromuscular blockade: skeletal muscle weakness, apnea, respiratory paralysis (high doses); arachnoiditis (intrathecal use). CV: hypotension or hypertension. GI: Nausea, vomiting, transient increase in AST, ALT, and serum LDH and bilirubin; hepatomegaly, splenomegaly. Hematologic: Increased or decreased reticulocyte counts; granulocytopenia, thrombocytopenia (fever, bleeding tendency), thrombocytopenic purpura, anemia. Body as a Whole: Hypersensitivity (rash, pruritus, urticaria, exfoliative dermatitis, eosinophilia, burning sensation of skin, drug fever, joint pains, laryngeal edema, anaphylaxis). Urogenital: Nephrotoxicity: proteinuria, tubular necrosis, cells or casts in urine, hematuria, rising BUN, nonprotein nitrogen, serum creatinine; decreased creatinine clearance. Other: Local irritation and pain following IM use; thrombophlebitis, abscess, superinfections, syndrome of hypocalcemia (tetany, weakness, hypokalemia, hypomagnesemia). Topical and Ophthalmic: Photosensitivity, sensitization, erythema, pruritus; burning, stinging, and lacrimation (ophthalmic formulation).

Interactions

Drug: Amphotericin B, capreomycin, cisplatin, methoxyflurane, polymyxin B, vancomycin, ethacrynic acid, and furosemide increase risk of nephrotoxicity. general anesthetics and neuromuscular blocking agents (e.g., succinylcholine) potentiate neuromuscular blockade. Indomethacin may increase gentamicin levels in neonates.

Pharmacokinetics

Absorption: Well absorbed from IM site. Peak: 30–90 min IM. Distribution: Widely distributed in body fluids, including ascitic, peritoneal, pleural, synovial, and abscess fluids; poor CNS penetration; concentrates in kidney and inner ear; crosses placenta. Metabolism: Not metabolized. Elimination: Excreted unchanged in urine; small amounts accumulate in kidney and are eliminated over 10–20 d; small amount excreted in breast milk. Half-Life: 2–4 h.

Nursing Implications

Assessment & Drug Effects

  • Lab tests: Perform C&S and renal function prior to first dose and periodically during therapy; therapy may begin pending test results. Determine creatinine clearance and serum drug concentrations at frequent intervals, particularly for patients with impaired renal function, infants (renal immaturity), older adults, patients receiving high doses or therapy beyond 10 d, patients with fever or extensive burns, edema, obesity.
  • Repeat C&S if improvement does not occur in 3–5 d; reevaluate therapy.
  • Note: Dosages are generally adjusted to maintain peak serum gentamicin concentrations of 4–10 mcg/mL, and trough concentrations of 1–2 mcg/mL. Prolonged peak concentrations above 12 mcg/mL and trough concentrations above 2 mcg/mL are associated with toxicity.
  • Draw blood specimens for peak serum gentamicin concentration 30 min–1h after IM administration, and 30 min after completion of a 30–60 min IV infusion. Draw blood specimens for trough levels just before the next IM or IV dose. Use nonheparinized tubes to collect blood.
  • Check baseline weight and vital signs; determine vestibular and auditory function before therapy and at regular intervals. Check vestibular and auditory function again 3–4 wk after drug is discontinued (the time that deafness is most likely to occur).
  • Monitor I&O. Keep patient well hydrated to prevent chemical irritation of renal tubules. Report oliguria, unusual appearance of urine, change in I&O ratio or pattern, and presence of edema (prolongs elimination time).
  • Note: Ototoxic effect (see Appendix F) is greatest on the vestibular branch of eighth cranial (acoustic) nerve (symptoms: headache, dizziness or vertigo, nausea and vomiting with motion, ataxia, nystagmus). However, damage to the auditory branch (tinnitus, roaring noises, sensation of fullness in ears, hearing impairment) may also occur. Report promptly to prevent permanent damage.
  • Watch for S&S of bacterial overgrowth (opportunistic infections) with resistant or nonsusceptible organisms (diarrhea, anogenital itching, vaginal discharge, stomatitis, glossitis).

Patient & Family Education

  • Note: When using topical applications: Avoid excessive exposure to sunlight because of danger of photosensitivity; withhold medication and notify physician if condition fails to improve within 1 wk, worsens, or signs of irritation or sensitivity occur; and apply medication as directed and only for length of time prescribed (overuse can result in superinfections).

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

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