TOBI (Page 3 of 7)

Clinical Considerations

Disease-Associated Maternal and/or Embryo/Fetal Risk

Cystic fibrosis may increase the risk for preterm delivery.

Data

Animal Data

No reproductive toxicity studies have been conducted with TOBI (tobramycin administered by inhalation). However, subcutaneous administration of tobramycin at doses of up to 100 (rat) or 20 (rabbit) mg/kg/day during organogenesis was not associated with adverse developmental outcomes. Doses of tobramycin ≥40 mg/kg/day were severely maternally toxic to rabbits and precluded the evaluation of adverse developmental outcomes. Ototoxicity was not evaluated in offspring during non-clinical reproductive toxicity studies with tobramycin.

8.2 Lactation

Risk Summary

There are no data on the presence of TOBI in either human or animal milk, the effects on the breastfed infant, or the effects on milk production. Limited published data on other formulations of tobramycin in lactating women indicate that tobramycin is present in human milk. However, systemic absorption of tobramycin following inhaled administration is expected to be minimal [see Clinical Pharmacology (12.3)]. Tobramycin may cause alteration in the intestinal flora of the breastfeeding infant (see Clinical Considerations). The developmental and health benefits of breastfeeding should be considered along with the mother’s clinical need for TOBI and any potential adverse effects on the breastfed infant from TOBI or from the underlying maternal condition.

Clinical Considerations

Tobramycin may cause intestinal flora alteration. Advise a woman to monitor the breastfed infant for loose or bloody stools and candidiasis (thrush, diaper rash).

8.4 Pediatric Use

The safety and efficacy of TOBI in pediatric patients under 6 years of age has not been established. The use of TOBI is not indicated in children <6 years of age [see Indications and Usage (1) and Dosage and Administration (2)].

8.5 Geriatric Use

Clinical studies of TOBI did not include patients aged 65 years and over. Tobramycin is known to be substantially excreted by the kidney, and the risk of adverse reactions to this drug may be greater in patients with impaired renal function. Because elderly patients are more likely to have decreased renal function, it may be useful to monitor renal function [see Warnings and Precautions (5.3)].

10 OVERDOSAGE

Signs and symptoms of acute toxicity from overdosage of intravenous (IV) tobramycin might include dizziness, tinnitus, vertigo, loss of high-tone hearing acuity, respiratory failure, neuromuscular blockade, and renal impairment. Administration by inhalation results in low systemic bioavailability of tobramycin. Tobramycin is not significantly absorbed following oral administration. Tobramycin serum concentrations may be helpful in monitoring overdosage.

Acute toxicity should be treated with immediate withdrawal of TOBI, and baseline tests of renal function should be undertaken.

In all cases of suspected overdosage, physicians should contact the Regional Poison Control Center for information about effective treatment. In the case of any overdosage, the possibility of drug interactions with alterations in drug disposition should be considered.

Hemodialysis may be helpful in removing tobramycin from the body.

11 DESCRIPTION

TOBI® is a tobramycin solution for inhalation. It is a sterile, clear, slightly yellow, non-pyrogenic, aqueous solution with the pH and salinity adjusted specifically for administration by a compressed air driven reusable nebulizer. The chemical formula for tobramycin is C18 H37 N5 O9 and the molecular weight is 467.52 g/mol. Tobramycin is O-3-amino-3-deoxy-α-D‑glucopyranosyl-(1→4)-O-[2,6-diamino-2,3,6- trideoxy-α-D-ribo-hexopyranosyl-(1→6)]-2-deoxy-L-streptamine. The structural formula for tobramycin is:

Tobramycin Structural Formula
(click image for full-size original)

Each single-dose 5 mL ampoule contains 300 mg tobramycin and 11.25 mg sodium chloride in sterile water for injection. Sulfuric acid and sodium hydroxide are added to adjust the pH to 6.0. Nitrogen is used for sparging. All ingredients meet USP requirements. The formulation contains no preservatives.

12 CLINICAL PHARMACOLOGY

12.1 Mechanism of Action

Tobramycin is an aminoglycoside antibacterial [see Microbiology (12.4)].

12.3 Pharmacokinetics

Absorption

TOBI contains tobramycin, a cationic polar molecule that does not readily cross epithelial membranes.(1) The bioavailability of TOBI may vary because of individual differences in nebulizer performance and airway pathology.(2) Following administration of TOBI, tobramycin remains concentrated primarily in the airways.

Serum Concentrations

The average serum concentration of tobramycin one hour after inhalation of a single 300-mg dose of TOBI by cystic fibrosis patients was 0.95 mcg/mL. After 20 weeks of therapy on the TOBI regimen, the average serum tobramycin concentration one hour after dosing was 1.05 mcg/mL.

Sputum Concentrations

Ten minutes after inhalation of the first 300-mg dose of TOBI by cystic fibrosis patients, the average concentration of tobramycin was 1237 mcg/g (range 35 to 7417 mcg/g) in sputum. Tobramycin does not accumulate in sputum; after 20 weeks of therapy with the TOBI regimen, the average concentration of tobramycin at ten minutes after inhalation was 1154 mcg/g (range 39 to 8085 mcg/g) in sputum. Two hours after inhalation, sputum concentrations declined to approximately 14% of tobramycin levels at ten minutes after inhalation.

Distribution

Following administration of TOBI, tobramycin remains concentrated primarily in the airways. Binding of tobramycin to serum proteins is negligible.

Elimination

Metabolism

Tobramycin is not metabolized.

Excretion

The elimination half-life of tobramycin from serum is approximately 2 and 3 hours after intravenous (IV) administration and inhalation, respectively. Systemically absorbed tobramycin is primarily excreted unchanged in the urine principally by glomerular filtration. Unabsorbed tobramycin, following TOBI administration, is probably eliminated primarily in expectorated sputum.

12.4 Microbiology

Mechanism of Action

Tobramycin is an aminoglycoside antibacterial produced by Streptomyces tenebrarius.(1) It acts primarily by disrupting protein synthesis, leading to altered cell membrane permeability, progressive disruption of the cell envelope, and eventual cell death.(3)

Tobramycin has in vitro activity against gram-negative bacteria including Pseudomonas aeruginosa. It is bactericidal in vitro at concentrations equal to or slightly greater than the minimum inhibitory concentration (MIC).

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