Genticin

Action

Destroys gram-negative bacteria by irreversibly binding to 30S subunit of bacterial ribosomes and blocking protein synthesis, resulting in misreading of genetic code and separation of ribosomes from messenger RNA

Availability

Cream: 0.1%

Injection: 10 mg/ml (pediatric), 40 mg/ml (adult)

I.V. infusion (premixed in normal saline solution): 40 mg, 60 mg, 70 mg, 80 mg, 90 mg, 100 mg, 120 mg

Ointment: 0.1%

Ointment (ophthalmic): 0.3% (base)

Solution (ophthalmic): 0.3% (base)

Indications and dosages

➣ Serious infections caused by Pseudomonas aeruginosa, Escherichia coli, and Proteus, Klebsiella, Serratia, Enterobacter, Citrobacter, or Staphylococcus species

Adults: 3 mg/kg/day in three divided doses I.M. or I.V. infusion q 8 hours. For life-threatening infections, up to 5 mg/kg/day in three to four divided doses; reduce to 3 mg/kg/day as indicated.

Children: 2 to 2.5 mg/kg q 8 hours I.M. or I.V. infusion

Infants older than 1 week: 2.5 mg/kg q 8 hours I.M. or I.V. infusion

Neonates younger than 1 week, preterm infants: 2.5 mg/kg q 12 hours I.M. or I.V. infusion. In preterm infants of less than 32 weeks' gestational age, 2.5 mg/kg q 18 hours or 3 mg/kg q 24 hours also may produce satisfactory peak and trough blood levels.

➣ Endocarditis prophylaxis before surgery

Adults: 1.5 mg/kg I.M. or I.V. 30 minutes before surgery, to a maximum of 80 mg. As prescribed, give with ampicillin or vancomycin.

Children: 2 mg/kg I.M. or I.V. 30 minutes before surgery, to a maximum of 80 mg

➣ External ocular infections caused by susceptible organisms

Adults and children: One to two drops of ophthalmic solution in eye q 4 hours. For serious infections, up to two drops q hour, or ophthalmic ointment applied to lower conjunctival sac two to three times daily.

➣ Treatment and prevention of superficial burns caused by susceptible bacteria

Adults and children older than age 1: Gently rub small a amount of drug topically on affected area three or four times daily.

Dosage adjustment

• Renal impairment

• Cystic fibrosis

Contraindications

• Hypersensitivity to drug or other aminoglycosides

Precautions

Use cautiously in:

• neuromuscular disease, renal impairment, hearing impairment

• sulfite sensitivity (with parenteral use)

• obese patients

• elderly patients

• pregnant or breastfeeding patients

• infants, neonates, and premature infants.

Administration

• Before starting therapy, obtain specimens as needed for culture and sensitivity testing.

• For I.V. infusion, dilute with 50 to 200 ml of dextrose 5% in water (D₅W) or normal saline solution, and administer over 30 minutes to 2 hours.

• After infusion, flush line with normal saline solution or D₅W.

• Obtain peak drug blood level 30 minutes after 30-minute infusion; obtain trough level within 30 minutes of next scheduled dose.

• Give cephalosporin or parenteral penicillin 1 hour before or after gentamicin, as prescribed.

• Know that for topical treatment of burns, gauze dressings may be applied.

Adverse reactions

CNS: dizziness, vertigo, tremors, numbness, depression, confusion, lethargy, headache, paresthesia, neuromuscular blockade, seizures, neurotoxicity

EENT: visual disturbances, dry eyes, nystagmus, photophobia, ototoxicity, hearing loss, tinnitus

GI: nausea, vomiting, stomatitis, increased salivation, splenomegaly, anorexia

GU: increased urinary casts, polyuria, dysuria, erectile dysfunction, azotemia, nephrotoxicity

Hematologic: eosinophilia, leukemoid reaction, hemolytic anemia, aplastic anemia, neutropenia, agranulocytosis, leukopenia, thrombocytopenia, pancytopenia

Hepatic: hepatomegaly, hepatotoxicity, hepatic necrosis

Musculoskeletal: joint pain, muscle twitching

Respiratory: apnea

Skin: exfoliative dermatitis, rash, pruritus, urticaria, purpura, alopecia

Other: weight loss, superinfection, pain and irritation at I.M. injection site

Interactions

Drug-drug. Acyclovir, amphotericin B, carboplatin, cephalosporins, cisplatin, loop diuretics, vancomycin, other ototoxic or nephrotoxic drugs: increased risk of ototoxicity and nephrotoxicity

Dimenhydrinate, other antiemetics: masking of ototoxicity symptoms

General anesthetics, neuromuscular blockers: increased activity of these drugs

Indomethacin: increased gentamicin peak and trough levels

Penicillins (such as ampicillin, ticarcillin): synergistic effect

Tacrolimus: nephrotoxicity

Drug-diagnostic tests. Alanine aminotransferase, aspartate aminotransferase, bilirubin, blood urea nitrogen (BUN), creatinine, lactate dehydrogenase: increased values

Granulocytes, hemoglobin, platelets, white blood cells: decreased values

Reticulocytes: increased or decreased count

Patient monitoring

• Watch for signs and symptoms of hypersensitivity reactions.

See Know that drug blood level monitoring is especially important in therapy lasting more than 5 days, acute or chronic renal impairment, extracellular fluid volume changes, obesity, infants younger than 3 months, concomitant use of nephrotoxic drugs, patients requiring higher doses or dosage interval adjustments (such as those with cystic fibrosis, endocarditis, or critical illness), and patients with signs or symptoms of nephrotoxicity or ototoxicity.

• Assess fluid intake and output, urine specific gravity, and urinalysis for signs of nephrotoxicity.

• Monitor CBC, BUN, creatinine level, and creatinine clearance.

• Weigh patient regularly.

• Assess for signs and symptoms of ototoxicity (hearing loss, tinnitus, ataxia, and vertigo).

Patient teaching

See Teach patient to recognize and immediately report signs and symptoms of hypersensitivity reaction, infection, unusual tiredness, yellowing of skin or eyes, and muscle twitching.

• Advise patient to report signs and symptoms of ototoxicity (hearing loss, ringing in ears, vertigo).

• Instruct patient to drink plenty of fluids to ensure adequate urine output.

• Tell patient to monitor urine output and report significant changes.

• Caution patient to avoid driving and other hazardous activities until he knows how drug affects concentration and alertness.

• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs and tests mentioned above.