TOBRASONE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for TOBRASONE (TOBRASONE).
Tobrasone is a combination of tobramycin (an aminoglycoside antibiotic that inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit) and dexamethasone (a corticosteroid that suppresses inflammation by inhibiting phospholipase A2, reducing prostaglandin and leukotriene synthesis).
| Metabolism | Tobramycin undergoes minimal hepatic metabolism; dexamethasone is primarily metabolized in the liver via CYP3A4. |
| Excretion | Renal elimination of unchanged drug and metabolites accounts for approximately 60-70% of the dose, with biliary/fecal excretion contributing 20-30%. |
| Half-life | Terminal elimination half-life is 2.5-3.5 hours in adults, supporting twice-daily dosing for maintenance therapy. |
| Protein binding | Plasma protein binding is 60-70%, primarily to albumin and alpha-1-acid glycoprotein. |
| Volume of Distribution | Volume of distribution is approximately 1.4-2.1 L/kg, indicating extensive tissue distribution with higher lung concentrations. |
| Bioavailability | Inhalation: 15-30% (due to first-pass metabolism); oral: <1% due to extensive hepatic metabolism. Intravenous: 100%. |
| Onset of Action | Inhalation: bronchodilation within 5-15 minutes; peak effect at 1-2 hours. |
| Duration of Action | Inhalation: 12 hours (bronchodilation); clinical improvement in asthma control sustained over 12 weeks with regular use. |
2 mg (as 0.2% topical solution) applied to the affected area twice daily. Not for ophthalmic use.
| Dosage form | SUSPENSION/DROPS |
| Renal impairment | No dose adjustment required based on GFR; systemic absorption minimal after topical application. |
| Liver impairment | No specific dose adjustment recommended; topical use results in negligible systemic exposure. |
| Pediatric use | Safety and efficacy in children below 12 years have not been established; use in adolescents (12-18 years) same as adult. |
| Geriatric use | No specific dose adjustment; use with caution due to potential for increased skin fragility and infection risk. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for TOBRASONE (TOBRASONE).
| Breastfeeding | Betamethasone: enters breast milk; near-endogenous levels at maternal doses <20 mg/day; risk of adrenal suppression in infant unknown. Tobramycin: not known if excreted into human milk; other aminoglycosides are found in low concentrations. M/P ratio not established. Use with caution; monitor infant for diarrhea, candidiasis, and adrenal suppression. |
| Teratogenic Risk | Corticosteroids, including tobramycin and betamethasone (components of TOBRASONE), are generally associated with increased risk of cleft palate in first trimester (odds ratio 1.3-3.4). Betamethasone crosses placenta; chronic high doses may cause intrauterine growth restriction and adrenal suppression in fetus. Tobramycin: aminoglycoside use in pregnancy is not recommended unless life-threatening infection; risk of fetal ototoxicity and nephrotoxicity, especially with prolonged therapy. No adequate human studies. Risk summary: avoid unless benefit outweighs risk. |
■ FDA Black Box Warning
None
| Common Effects | Application site reactions burning irritation itching and redness Blurred vision |
| Serious Effects |
["Hypersensitivity to tobramycin, dexamethasone, or any component","Epithelial herpes simplex keratitis (dendritic keratitis)","Vaccinia, varicella, and other viral diseases of the cornea and conjunctiva","Mycobacterial infections of the eye","Fungal diseases of the eye"]
| Precautions | ["Prolonged use may lead to ocular hypertension/glaucoma","Corticosteroids may mask or exacerbate infections","Increased risk of secondary fungal infections","Avoid prolonged use to prevent cataract formation","Not for injection or intraocular use"] |
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| Fetal Monitoring | Maternal: baseline and periodic audiometry (tobramycin ototoxicity), renal function (serum creatinine, BUN), and drug levels (tobramycin trough <2 µg/mL, peak 5-10 µg/mL). Fetal: ultrasound for growth restriction, amniotic fluid volume; consider fetal adrenal suppression assessment if high-dose betamethasone used. Monitor for signs of infection. |
| Fertility Effects | No specific human data. Corticosteroids may impair spermatogenesis in males and cause menstrual irregularities in females. Aminoglycosides have no known direct effect on fertility. Animal studies: no adverse reproductive outcomes at clinical doses. |