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 |
| Molecular Weight | tobramycin: 467.5 Da; dexamethasone: 392.5 Da |
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 | Corticosteroids and tobramycin cross the placenta. Topical administration reduces systemic exposure, but use only if potential benefit outweighs risk. Avoid in first trimester unless essential. |
| 2nd trimester | Limited data; topical use considered low risk due to minimal systemic absorption. Monitor for potential paternal toxicity with aminoglycosides. |
| 3rd trimester | Use only if clearly needed. Prolonged high-dose corticosteroids may cause fetal adrenal suppression, but topical route minimizes risk. |
Clinical note
Comprehensive clinical and safety monograph for TOBRADEX ST (TOBRADEX ST).
| Placental transfer | Corticosteroids and tobramycin cross the placenta; systemic absorption after ocular administration is minimal, but transfer can occur at detectable levels with high doses or prolonged use. |
| Breastfeeding | Tobramycin and corticosteroids are excreted into human milk in small amounts after topical ocular use. Systemic absorption is negligible, so risk to infant is low. However, caution in premature infants or those with renal impairment. Monitor for signs of gastrointestinal effects or candidiasis. |
■ FDA Black Box Warning
None
| Serious Effects |
Hypersensitivity to any componentEpithelial herpes simplex keratitis (dendritic keratitis)Vaccinia, varicella, and other viral infections of the cornea and conjunctivaMycobacterial infections of the eyeFungal diseases of ocular structuresUntreated purulent infections
| 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 |
| Food/Dietary | No significant food interactions reported. Systemic absorption is minimal with ophthalmic use. No specific dietary restrictions required. |
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| Lactation Rating | L2 (probably compatible) |
| 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. |
| 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. |
| Clinical Pearls | TOBRADEX ST is a fixed-dose combination of tobramycin (0.3%) and loteprednol etabonate (0.5%) used for steroid-responsive inflammatory ocular conditions with superficial bacterial infection or risk of infection. The 'ST' denotes a specialized suspension technology that improves drug delivery to the anterior chamber. Use caution in patients with glaucoma, as loteprednol can increase intraocular pressure (IOP); monitor IOP regularly. Avoid prolonged use (>2 weeks) without reassessment due to risk of secondary infections, cataract formation, and IOP elevation. Do not administer while wearing contact lenses; lenses should be removed before instillation and reinserted after 15 minutes. Shake vigorously before each use. In pediatric patients, systemic absorption may be greater; monitor for adrenal suppression if used long-term. |
| Patient Advice | Shake the bottle well before each use. · Wash hands before applying the drops. · Tilt head back, pull down lower eyelid, and apply the prescribed number of drops into the affected eye(s). · Do not touch the dropper tip to any surface to avoid contamination. · Remove contact lenses before using and wait at least 15 minutes before reinserting. · Do not use this medication for longer than prescribed without consulting your doctor. · Report any vision changes, eye pain, redness, swelling, or discharge that worsens. · If you miss a dose, apply it as soon as you remember. If it is almost time for your next dose, skip the missed one and resume your regular schedule. Do not double-dose. · Store at room temperature away from moisture and heat. Do not freeze. · Keep this medication out of reach of children. |