TOBRADEX ST
Clinical safety rating: caution
Comprehensive clinical and safety monograph for TOBRADEX ST (TOBRADEX ST).
Tobramycin is an aminoglycoside antibiotic that binds to the 30S ribosomal subunit, inhibiting bacterial protein synthesis. Dexamethasone is a corticosteroid that suppresses inflammation by binding to glucocorticoid receptors, inhibiting phospholipase A2, and reducing prostaglandin and leukotriene synthesis.
| Metabolism | Tobramycin is primarily excreted unchanged by the kidneys; minimal hepatic metabolism. Dexamethasone is metabolized in the liver via CYP3A4. |
| Excretion | Renal: ~60% as unchanged drug and inactive metabolites; Biliary: ~20%; Fecal: ~20% |
| Half-life | Tobramycin: 2-3 hours (prolonged in renal impairment; up to 50-70 hours in anuria); Dexamethasone: 3-4 hours |
| Protein binding | Tobramycin: <30% bound to plasma proteins; Dexamethasone: ~77% bound to albumin |
| Volume of Distribution | Tobramycin: Vd 0.26 L/kg (distributes primarily in extracellular fluid); Dexamethasone: Vd 0.8-1.0 L/kg (distributes widely including CSF) |
| Bioavailability | Ophthalmic suspension: Systemic absorption minimal but occurs via nasolacrimal duct; combined systemic bioavailability <1% from ocular dose |
| Onset of Action | Ophthalmic suspension: Onset of anti-inflammatory effect within 24 hours; antibacterial effect within 1-2 hours |
| Duration of Action | Ophthalmic suspension: Duration of anti-inflammatory effect is approximately 24-48 hours with q.i.d. dosing; antibacterial effect persists for 12-24 hours |
1 drop into the conjunctival sac of the affected eye(s) every 4 to 6 hours; in severe cases, may be increased to 1 drop every 2 hours. Do not prescribe more than 20 mL per 30 days.
| Dosage form | SUSPENSION/DROPS |
| Renal impairment | No dosage adjustment required for ophthalmic use. |
| Liver impairment | No dosage adjustment required for ophthalmic use. |
| Pediatric use | Safety and efficacy in pediatric patients have not been established; use only if potential benefit outweighs risk. |
| Geriatric use | No specific dosage adjustment recommended; use with caution due to potential intraocular pressure elevation and cataract formation. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for TOBRADEX ST (TOBRADEX ST).
| Breastfeeding | Dexamethasone and tobramycin are excreted into breast milk. Dexamethasone: Peak milk levels ~7-27% of maternal serum; minimal with ophthalmic use. Tobramycin: Low oral bioavailability (<1%), infant exposure negligible via milk. M/P ratio not established for ophthalmic route. American Academy of Pediatrics considers compatible with breastfeeding. Monitor infant for diarrhea, rash, or candidiasis. |
| Teratogenic Risk | Corticosteroids and tobramycin: Corticosteroids (dexamethasone) are associated with increased risk of cleft palate (first trimester) and fetal growth restriction, adrenal suppression, and cataract (second/third trimester). Tobramycin: Potential for ototoxicity (eighth cranial nerve damage) and nephrotoxicity, especially with prolonged systemic exposure; however, ophthalmic use results in minimal systemic absorption. Risk in first trimester: theoretical based on other aminoglycosides. Second/third trimester: potential fetal ototoxicity with high systemic levels. Overall, low risk with proper ophthalmic dosing but caution advised. |
■ FDA Black Box Warning
None
| Serious Effects |
["Hypersensitivity to any component of the product","Epithelial herpes simplex keratitis (dendritic keratitis)","Vaccinia, varicella, and other viral infections of the cornea and conjunctiva","Mycobacterial infections of the eye","Fungal diseases of ocular structures","Untreated purulent ocular infections (e.g., gonococcal, chlamydial)"]
| Precautions | ["Prolonged use may lead to ocular hypertension/glaucoma, cataract formation, secondary infection, and delayed wound healing","Risk of secondary fungal or viral infections; discontinue if superinfection occurs","Not for injection; do not administer subconjunctivally or intraocularly","May cause corneal thinning or perforation in patients with corneal disease","Use with caution in patients with known or suspected glaucoma, as intraocular pressure may increase","Use in children may require monitoring; safety in pediatric patients not established","Systemic absorption may occur, especially with prolonged use; caution in renal impairment"] |
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| Fetal Monitoring | Ophthalmic use: no specific fetal monitoring required due to low systemic absorption. If used chronically or at high doses, consider maternal intraocular pressure monitoring (glaucoma risk) and fetal growth assessment (ultrasound) for prolonged corticosteroid exposure. Newborn: observe for signs of adrenal suppression if high maternal systemic exposure. |
| Fertility Effects | No human data on fertility effects of ophthalmic dexamethasone/tobramycin. Animal studies: corticosteroids may impair fertility; tobramycin did not affect fertility in rats. Ophthalmic use unlikely to significantly affect fertility due to low systemic absorption. |