tobramycin (Rx)

Brand and Other Names:Nebcin injection
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Dosing & Uses

AdultPediatric

Dosage Forms & Strengths

injectable solution

  • 10mg/mL
  • 40mg/mL

Solution reconstituted

  • 1.2g

Bacterial Infections

3-6 mg/kg/day IV/IM divided q8hr OR  

4-7 mg/kg/dose IV/IM qDay

Renal Impairment

Clcr >60 mL/min: q8hr

Clcr 40-60 mL/min: q12hr

Clcr 20-40 mL/min: q24hr

Clcr 10-20 mL/min: q48hr

Clcr <10 mL/min: q72hr

Following dialysis in ESRD

Monitor

Peak and trough concentrations, renal and auditory function

Life-threatening infection: 8-10 mcg/mL

Serious infection: 6-8 mcg/mL

UTIs: 4-6 mcg/mL

Synergy for infections caused by gram-positive organisms: 3-5 mcg/mL

Other Indications & Uses

May have increase activity against resistant Gram negatives

Citrobacter spp., E. coli, P. aeruginosa, Proteus spp. (indole-positive and negative), Providencia spp. (including Klebsiella-Enterobacter-Serratia), S. aureus (coagulase-positive and negative)

Dosage Forms & Strengths

injectable solution

  • 10mg/mL
  • 40mg/mL

Cystic Fibrosis

IV/IM: 2.5-3.3 mg/kg q6-8hr  

Neonates

<30 week gestation

  • <28 days old: 2.5 mg/kg IV/IM qDay
  • ≥28 days old: 3 mg/kg IV/IM qDay

30-36 week gestation

  • <14 days old: 3 mg/kg IV/IM qDay
  • ≥14 days old: 5 mg/kg/day IV/IM divided q12hr

>37 week gestation

  • <7 days old: 5 mg/kg/day IV/IM divided q12hr
  • ≥7 days old: 7.5 mg/kg/day IV/IM divided q8hr

Bacterial Infection

<5 years old: 2.5 mg/kg/dose IV/IM q8hr  

≥5 years old: 2-2.5 mg/kg/dose IV/IM q8hr

Hemodialysis: 1.25-1.75 mg/kg/dose postdialysis

Monitor

Peak and trough concentrations, renal and auditory function

Life-threatening infection: 8-10 mcg/mL

Serious infection: 6-8 mcg/mL

UTIs: 4-6 mcg/mL

Synergy for infections caused by gram-positive organisms: 3-5 mcg/mL

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Interactions

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and tobramycin

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            Adverse Effects

            1-10%

            Ototoxicity

            Nephrotoxicity

            Neurotoxicity (neuromuscular blockade)

            <1%

            Hypotension

            Drug fever

            Drowsiness

            Headache

            Paresthesia

            Tremor

            Rash

            Nausea

            Vomiting

            Anemia

            Eosinophilia

            Arthralgia

            Weakness

            Eyelid edema

            Itching eyes

            Keratitis

            Lacrimation

            Dyspnea

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            Warnings

            Black Box Warnings

            Neurotoxicity, manifested as both bilateral auditory and vestibular ototoxicity, can occur in patients with preexisting renal damage and in patients with normal renal function treated at higher doses and/or for periods longer than those recommended; high-frequency deafness usually occurs first and can be detected only by audiometric testing; vertigo may occur and may be evidence of vestibular injury

            Patients who develop cochlear damage may not have symptoms during therapy to warn them of eighth-nerve toxicity, and partial or total irreversible bilateral deafness may continue to develop after the drug has been discontinued

            When feasible, recommended that serial audiograms be obtained in patients old enough to be tested, particularly high-risk patients; evidence of impairment of renal, vestibular, or auditory function requires discontinuation of drug or dosage adjustment

            Aminoglycosides are potentially nephrotoxic; risk is greater in patients with impaired renal function and in those who receive high doses or prolonged therapy; rarely, nephrotoxicity may not become apparent until the first few days after cessation of therapy

            Use with caution in premature infants and neonates because of renal immaturity and the resulting prolongation of serum half-life of the drug

            Neuromuscular blockade and respiratory paralysis have been reported following parenteral injection, topical instillation (as in orthopedic and abdominal irrigation or in local treatment of empyema), and oral use of aminoglycosides, especially when given soon after anesthesia or muscle relaxants; if blockage occurs, calcium salts may reverse these phenomena, but mechanical respiratory assistance may be necessary

            Avoid concurrent or sequential use of neurotoxic and/or nephrotoxic drugs including other aminoglycosides (eg, amikacin, streptomycin, neomycin, kanamycin, gentamicin, paromomycin

            Cumulative listing of drugs to avoid from all aminoglycoside package inserts includes amphotericin B, bacitracin, cephaloridine, cisplatin, colistin, polymyxin B, vancomycin, and viomycin. Avoid potent diuretics (eg, ethacrynic acid, furosemide) because they increase risk of ototoxicity. When administered intravenously, diuretics may enhance aminoglycoside toxicity by altering antibiotic concentrations in serum and tissue

            Contraindications

            Documented hypersensitivity to any aminoglycoside or history of hypersensitivity or serious toxic reactions to aminoglycosides

            Cautions

            Serious allergic sometimes fatal reactions including anaphylaxis and dermatologic reactions including exfoliative dermatitis, toxic epidermal necrolysis, erythema multiforme, and Stevens-Johnson Syndrome reported rarely; discontinue therapy If allergic reaction occurs, drug should be discontinued and appropriate therapy instituted

            Serum and urine specimens for examination should be collected during therapy; serum calcium, magnesium, and sodium should be monitored

            Cross-allergenicity among aminoglycosides has been demonstrated

            In patients with extensive burns or cystic fibrosis, altered pharmacokinetics may result in reduced serum concentrations of aminoglycosides; in such patients treated with tobramycin, measurement of serum concentration is especially important as a basis for determination of appropriate dosage

            Elderly patients may have reduced renal function that may not be evident in results of routine screening tests, such as BUN or serum creatinine; a creatinine clearance determination may be more useful; monitoring of renal function during treatment with aminoglycosides is particularly important in such patients

            An increased incidence of nephrotoxicity reported following concomitant administration of aminoglycoside antibiotics and cephalosporins

            Aminoglycosides should be used with caution in patients with muscular disorders, such as myasthenia gravis or parkinsonism, since these drugs may aggravate muscle weakness because of potential curare-like effect on neuromuscular function

            Aminoglycosides may be absorbed in significant quantities from body surfaces after local irrigation or application and may cause neurotoxicity and nephrotoxicity

            Aminoglycosides have not been approved for intraocular and/or subconjunctival use; physicians are advised that macular necrosis has been reported following administration of aminoglycosides, including tobramycin, by these routes

            The inactivation of tobramycin and other aminoglycosides by ß-lactam-type antibiotics (penicillins or cephalosporins) has been demonstrated in vitro and in

            patients with severe renal impairment; such inactivation has not been found in patients with normal renal function who have been given the drugs by separate routes of administration

            Therapy with tobramycin may result in overgrowth of nonsusceptible organisms; if overgrowth of nonsusceptible organisms occurs, appropriate therapy should be initiated

            Clostridium difficile

            • Clostridium difficile associated diarrhea (CDAD) reported; may range
            • in severity from mild diarrhea to fatal colitis; treatment with antibacterial agents alters normal flora of colon leading to overgrowth of C. difficile
            • C. difficile produces toxins A and B which contribute to development of CDAD; hypertoxin producing strains of C. difficile cause increased morbidity and mortality
            • As these infections can be refractory to antimicrobial therapy and may require colectomy; CDAD must be considered in all patients who present with diarrhea following antibiotic use
            • Careful medical history is necessary since CDAD has been reported to occur over two months after the administration of antibacterial agents
            • If CDAD is suspected or confirmed, ongoing antibiotic use not directed against C. difficile may need to be discontinued
            • Appropriate fluid and electrolyte management, protein supplementation, antibiotic treatment of C. difficile, and surgical evaluation should be instituted as clinically indicated

            Peak and trough levels

            • Peak and trough serum levels should be measured periodically during therapy; prolonged concentrations above 12 mcg/mL should be avoided
            • Rising trough levels (above 2 mcg/mL) may indicate tissue accumulation; such accumulation, advanced age, and cumulative dosage may contribute to ototoxicity and nephrotoxicity; it is particularly important to monitor serum levels closely in patients with known renal impairment.
            • A useful guideline would be to perform serum level assays after 2 or 3 doses, so that dosage could be adjusted if necessary, and at 3- to 4-day intervals during therapy
            • In the event of changing renal function, more frequent serum levels should be obtained and the dosage or dosage interval adjusted according to guidelines
            • In order to measure the peak level, a serum sample should be drawn about 30 minutes following intravenous infusion or 1 hour after an intramuscular injection
            • Trough levels are measured by obtaining serum samples at 8 hours or just prior to next dose; these suggested time intervals are intended only as guidelines and may vary according to institutional practices
            • It is important, that there be consistency within individual patient program unless computerized pharmacokinetic dosing programs are available in the institution
            • Serum-level assays may be especially useful for monitoring treatment of severely ill patients with changing renal function or of those infected with less susceptible organisms or those receiving maximum dosage

            Neuromuscular blockade

            • Neuromuscular blockade and respiratory paralysis have been reported in cats receiving very high doses of tobramycin (40 mg/kg)
            • Possibility of prolonged or secondary apnea should be considered if tobramycin is administered to anesthetized patients who are also receiving neuromuscular blocking agents, such as succinylcholine, tubocurarine, or decamethonium, or to patients receiving massive transfusions of citrated blood
            • If neuromuscular blockade occurs, may be reversed by administration of calcium salts
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            Pregnancy & Lactation

            Pregnancy

            Total irreversible bilateral congenital deafness reported in children whose mother received another aminoglycoside (streptomycin) during pregnancy

            Serious side effects to fetus/infant not reported following use of aminoglycoside but potential for harm exists

            Lactation:

            Drug is present in breast milk following injection; aminoglycosides have poor oral bioavailability; may consider breastfeeding following injection

            Pregnancy Categories

            A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.

            B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.

            C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.

            D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.

            X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.

            NA: Information not available.

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            Pharmacology

            Mechanism of Action

            Inhibits protein synthesis by irreversibly binding to bacterial 30S and 50S ribosomes

            Absorption

            Absorption: IM: rapid and complete

            Peak Plasma Time: IM: 30-60 min; IV: ~30 min

            Distribution

            Distribution: to extracellular fluid including serum, abscesses, ascitic, pericardial, pleural, synovial, lymphatic, and peritoneal fluids; crosses placenta; poor penetration into CSF, eye, bone, prostate

            Protein Bound: <30%

            Vd: 0.2-0.3 L/kg; pediatrics: 0.2-0.7 L/kg

            Elimination

            Half-Life: 2-3 hr (normal renal function)

            Excretion: ~90%-95% in urine within 24 hr (normal renal function)

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            Administration

            IV Incompatibilities

            Additive: cefamandole, cefepime, cefotaxime, cefotetan, floxacillin, heparin, penicillins

            Syringe: cefamandole, clindamycin, heparin

            Y-site: allopurinol, amphotericin B cholesteryl sulfate, cefoperazone, heparin, hetastarch, indomethacin, propofol, sargramostim

            IV Preparation

            Standard diluent: 50-100 mL of D5W or NS

            IV Administration

            Infuse over 30-60 min

            Give penicillins or cephalosporins at least 1 hr apart from tobramycin

            Storage

            Stable at room temp both as the clear, colorless solution & as the dry powder

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            Formulary

            FormularyPatient Discounts

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            Tier Description
            1 This drug is available at the lowest co-pay. Most commonly, these are generic drugs.
            2 This drug is available at a middle level co-pay. Most commonly, these are "preferred" (on formulary) brand drugs.
            3 This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs.
            4 This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs or specialty prescription products.
            5 This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs or specialty prescription products.
            6 This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs or specialty prescription products.
            NC NOT COVERED – Drugs that are not covered by the plan.
            Code Definition
            PA Prior Authorization
            Drugs that require prior authorization. This restriction requires that specific clinical criteria be met prior to the approval of the prescription.
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            Drugs that have step therapy associated with each prescription. This restriction typically requires that certain criteria be met prior to approval for the prescription.
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            Medscape prescription drug monographs are based on FDA-approved labeling information, unless otherwise noted, combined with additional data derived from primary medical literature.