Tobramycin Drug Information

Tobramycin may be given intramuscularly or intravenously. Recommended dosages are the same for both routes. This insert is for a Pharmacy Bulk Package and is intended for preparing I.V. admixtures only.

Dosage recommendations for intramuscular use are for informational purposes only. The patient’s pretreatment body weight should be obtained for calculation of correct dosage. It is desirable to measure both peak and trough serum concentrations (see WARNINGS box and PRECAUTIONS ).

The dosage should be reduced to 3 mg/kg/day as soon as clinically indicated. To prevent increased toxicity due to excessive blood levels, dosage should not exceed 5 mg/kg/day unless serum levels are monitored (see WARNINGS box and PRECAUTIONS ). It is desirable to limit treatment to a short term.

The usual duration of treatment is 7 to 10 days. A longer course of therapy may be necessary in difficult and complicated infections. In such cases, monitoring of renal, auditory, and vestibular functions is advised, because neurotoxicity is more likely to occur when treatment is extended longer than 10 days.

Dosage in Patients with Cystic Fibrosis — In patients with cystic fibrosis, altered pharmacokinetics may result in reduced serum concentrations of aminoglycosides. Measurement of tobramycin serum concentration during treatment is especially important as a basis for determining appropriate dose. In patients with severe cystic fibrosis, an initial dosing regimen of 10 mg/kg/day in 4 equally divided doses is recommended.

This dosing regimen is suggested only as a guide. The serum levels of tobramycin should be measured directly during treatment due to wide interpatient variability. Administration for Patients with Impaired Renal Function — Whenever possible, serum tobramycin concentrations should be monitored during therapy.

Following a loading dose of 1 mg/kg, subsequent dosage in these patients must be adjusted, either with reduced doses administered at 8-hour intervals or with normal doses given at prolonged intervals. Both of these methods are suggested as guides to be used when serum levels of tobramycin cannot be measured directly. They are based on either the creatinine clearance or the serum creatinine of the patient because these values correlate with the half-life of tobramycin.

The dosage schedule derived from either method should be used in conjunction with careful clinical and laboratory observations of the patient and should be modified as necessary. Neither method should be used when dialysis is being performed. Reduced dosage at 8-hour Intervals — When the creatinine clearance rate is 70 mL or less per minute or when the serum creatinine value is known, the amount of the reduced dose can be determined by multiplying the normal dose from Table 3 by the percent of normal dose from the accompanying nomogram.

An alternate rough guide for determining reduced dosage at 8-hour intervals (for patients whose steady-state serum creatinine values are known) is to divide the normally recommended dose by the patient’s serum creatinine. Scales have been adjusted to facilitate dosage calculations. Normal Dosage at Prolonged Intervals — If the creatinine clearance rate is not available and the patient’s condition is stable, a dosage frequency in hours for the dosage given in Table 3 can be determined by multiplying the patient’s serum creatinine by 6. Dosage in Obese Patients — The appropriate dose may be calculated by using the patient’s estimated lean body weight plus 40% of the excess as the basic weight on which to figure mg/kg.

For pediatric patients, the volume of diluent should be proportionately less than that for adults. The diluted solution usually should be infused over a period of 20 to 60 minutes. Infusion periods of less than 20 minutes are not recommended because peak serum levels may exceed 12 mcg/mL (see WARNINGS box).

Tobramycin Injection, USP should not be physically premixed with other drugs but should be administered separately according to the recommended dose and route. Parenteral drug products should be inspected visually for particulate matter and discoloration prior to administration, whenever solution and container permit. Directions for Proper Use of Pharmacy Bulk Package Use Aseptic Technique – Not for Direct Infusion The pharmacy bulk package is for use in a Pharmacy Admixture Service only. 1.

For hanger application, peel off the paper liner from both ends of the tape hanger to expose 3/4 in. long adhesive portions. Adhere each end to the label on the bottle. 2. During use, container must be stored and all manipulations performed in an appropriate laminar flow hood. 3.

Remove cover from container and cleanse closure with antiseptic. 4. A single entry through the vial closure should be made with a sterile dispensing set which allows measured dispensing of the contents. Transfer individual dose(s) to appropriate intravenous infusion solutions without delay.

Use of a syringe with needle is not recommended as it may cause leakage. Multiple entries will also increase the potential of microbial and particulate contamination. The above process should be carried out under a laminar flow hood using aseptic technique.

ANY UNUSED PORTION MUST BE DISCARDED WITHIN 4 HOURS.

Neurotoxicity — Adverse effects on both the vestibular and auditory branches of the eighth nerve have been noted, especially in patients receiving high doses or prolonged therapy, in those given previous courses of therapy with an ototoxin, and in cases of dehydration. Symptoms include dizziness, vertigo, tinnitus, roaring in the ears, and hearing loss. Hearing loss is usually irreversible and is manifested initially by diminution of high-tone acuity.

Tobramycin and gentamicin sulfates closely parallel each other in regard to ototoxic potential. Nephrotoxicity — Renal function changes, as shown by rising BUN, NPN, and serum creatinine and by oliguria, cylindruria, and increased proteinuria, have been reported, especially in patients with a history of renal impairment who are treated for longer periods or with higher doses than those recommended. Adverse renal effects can occur in patients with initially normal renal function.

Clinical studies and studies in experimental animals have been conducted to compare the nephrotoxic potential of tobramycin and gentamicin. In some of the clinical studies and in the animal studies, tobramycin caused nephrotoxicity significantly less frequently than gentamicin. In some other clinical studies, no significant difference in the incidence of nephrotoxicity between tobramycin and gentamicin was found.

Other reported adverse reactions possibly related to tobramycin sulfate include anemia, granulocytopenia, and thrombocytopenia; and fever, rash, exfoliative dermatitis, itching, urticaria, nausea, vomiting, diarrhea, headache, lethargy, pain at the injection site, mental confusion, and disorientation. Laboratory abnormalities possibly related to tobramycin include increased serum transaminases (SGOT, SGPT); increased serum LDH and bilirubin; decreased serum calcium, magnesium, sodium, and potassium; and leukopenia, leukocytosis, and eosinophilia.

A hypersensitivity to any aminoglycoside is a contraindication to the use of tobramycin. A history of hypersensitivity or serious toxic reactions to aminoglycosides may also contraindicate the use of any other aminoglycoside because of the known cross-sensitivity of patients to drugs in this class.

Signs and Symptoms— The severity of the signs and symptoms following a tobramycin overdose are dependent on the dose administered, the patient’s renal function, state of hydration, and age and whether or not other medications with similar toxicities are being administered concurrently. Toxicity may occur in patients treated more than 10 days, in adults given more than 5 mg/kg/day, children given more than 7.5 mg/kg/day, or patients with reduced renal function whose dose has not been appropriately adjusted. Nephrotoxicity following the parenteral administration of an aminoglycoside is most closely related to the area under the curve of the serum concentration versus time graph.

Nephrotoxicity is more likely if trough blood concentrations fail to fall below 2 mcg/mL and is also proportional to the average blood concentration. Patients who are elderly, have abnormal renal function, are receiving other nephrotoxic drugs, or are volume depleted are at greater risk for developing acute tubular necrosis. Auditory and vestibular toxicities have been associated with aminoglycoside overdose.

These toxicities occur in patients treated longer than 10 days, in patients with abnormal renal function, in dehydrated patients, or in patients receiving medications with additive auditory toxicities. These patients may not have signs or symptoms or may experience dizziness, tinnitus, vertigo, and a loss of high-tone acuity as ototoxicity progresses. Ototoxicity signs and symptoms may not begin to occur until long after the drug has been discontinued.

Neuromuscular blockade or respiratory paralysis may occur following administration of many aminoglycosides. Neuromuscular blockade, respiratory failure, and prolonged respiratory paralysis may occur more commonly in patients with myasthenia gravis or Parkinson’s disease. Prolonged respiratory paralysis may also occur in patients receiving decamethonium, tubocurarine, or succinylcholine.

If neuromuscular blockade occurs, it may be reversed by the administration of calcium salts but mechanical assistance may be necessary. If tobramycin were ingested, toxicity would be less likely because aminoglycosides are poorly absorbed from an intact gastrointestinal tract. Treatment— In all cases of suspected overdosage, call your Regional Poison Control Center to obtain the most up-to-date information about the treatment of overdose.

This recommendation is made because, in general, information regarding the treatment of overdosage may change more rapidly than the package insert. In managing overdosage, consider the possibility of multiple drug overdoses, interaction among drugs, and unusual drug kinetics in your patient. The initial intervention in a tobramycin overdose is to establish an airway and ensure oxygenation and ventilation.

Resuscitative measures should be initiated promptly if respiratory paralysis occurs. Patients that have received an overdose of tobramycin and have normal renal function should be adequately hydrated to maintain a urine output of 3 to 5 mL/kg/hr. Fluid balance, creatinine clearance, and tobramycin plasma levels should be carefully monitored until the serum tobramycin level falls below 2 mcg/mL.

Patients in whom the elimination half-life is greater than 2 hours or whose renal function is abnormal may require more aggressive therapy. In such patients, hemodialysis may be beneficial.