Drug Study – Gentamicin Sulfate

Garamycin, Garamycin Ophthalmic, Genoptic

Classifications: antiinfective; aminoglycoside antibiotic


Broad-spectrum aminoglycoside antibiotic derived from Micromonospora purpurea. Action is usually bacteriocidal.


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.

Dosage and Route:

Moderate to Severe Infection
Adult: IV/IM 1.5–2 mg/kg loading dose followed by 3–5 mg/kg/d in 2–3 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 3–4 divided doses Intrathecal >3 mo, 1–2 mg preservative free q.d.
Neonate: IV/IM 2.5 mg/kg q12–24h
Acute Pelvic Inflammatory Disease
Adult: IV/IM 2 mg/kg followed by 1.5 mg/kg q8h
Prophylaxis of Bacterial Endocarditis
Adult: IV/IM 1.5 mg/kg 30 min before procedure, may repeat in 8 h
Child: IV/IM < 27 kg, 2 mg/kg 30 min before procedure, may repeat in 8 h

Adverse Effects:

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).


History of hypersensitivity to or toxic reaction with any aminoglycoside antibiotic. Safe use during pregnancy (category C) or lactation is not established

Nursing Responsibility:

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 g/mL, and trough concentrations of 1–2 g/mL. Peak concentrations above 12 g/mL and trough concentrations above 2 g/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.


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