Usage
Dexamethasone + Hydroxypropylmethylcellulose + Tobramycin ophthalmic suspension/ointment is prescribed for steroid-responsive inflammatory ocular conditions with co-existing or anticipated bacterial infection. This includes blepharitis, conjunctivitis, keratitis, and other inflammatory conditions of the palpebral and bulbar conjunctiva, cornea, and anterior segment of the globe. It is also used prophylactically after cataract surgery. Hydroxypropyl methylcellulose is a lubricant that relieves dry eyes and eye irritation.
Pharmacological Classification:
- Tobramycin: Aminoglycoside antibiotic
- Dexamethasone: Corticosteroid, anti-inflammatory
- Hydroxypropyl methylcellulose: Lubricant
Mechanism of Action:
- Tobramycin inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit.
- Dexamethasone suppresses the inflammatory response by inhibiting multiple inflammatory pathways.
- Hydroxypropyl methylcellulose lubricates the ocular surface, providing temporary relief from dryness and irritation.
Alternate Names
This combination is commonly known as Tobradex. Amgydex is another name for this combination.
How It Works
Pharmacodynamics:
Tobramycin exerts bactericidal activity against susceptible bacteria. Dexamethasone suppresses inflammation by inhibiting the migration of neutrophils and decreasing capillary permeability. Hydroxypropylmethylcellulose increases tear film viscosity and reduces evaporation.
Pharmacokinetics:
Tobramycin and dexamethasone, when administered topically to the eye, reach therapeutic concentrations in ocular tissues. Systemic absorption is low, minimizing systemic side effects. Tobramycin is eliminated primarily renally. Dexamethasone is metabolized by the liver, mainly via CYP3A4, and excreted in the urine. Hydroxypropyl methylcellulose is not absorbed systemically.
Dosage
Standard Dosage
Adults:
- Ophthalmic Suspension: Instill 1-2 drops into the affected eye(s) every 4-6 hours. In the initial 24-48 hours, the frequency can be increased to every 2 hours.
- Ophthalmic Ointment: Apply a ½-inch ribbon into the affected eye(s) up to 3-4 times daily, or at bedtime as an adjunct to drops.
Children:
- Children 2 years and older: Same as adult dosage. Safety and efficacy in children younger than 2 years have not been established.
Special Cases:
- Elderly Patients: Dosage adjustments are not usually required.
- Patients with Renal Impairment: Due to the low systemic absorption of tobramycin and dexamethasone following topical ocular administration, dose adjustments are not typically necessary. However, caution should be exercised in patients with severe renal impairment.
- Patients with Hepatic Dysfunction: Similarly, dose modifications are usually not required for hepatic impairment, but caution should be exercised in patients with severe hepatic impairment.
- Patients with Comorbid Conditions: Caution is advised in patients with glaucoma, diabetes, or a history of herpes simplex. Intraocular pressure should be monitored in these patient populations.
Side Effects
Common Side Effects:
- Eye irritation
- Burning or stinging
- Itching
- Redness
- Tearing
- Foreign body sensation
Rare but Serious Side Effects:
- Allergic reactions (e.g., rash, hives, swelling)
- Signs of eye infection (e.g., increased pain, discharge, vision changes)
- Increased intraocular pressure
- Glaucoma
- Cataract formation
- Corneal or scleral thinning/perforation
Contraindications
- Hypersensitivity to tobramycin, dexamethasone, or any component of the formulation
- Herpes simplex keratitis
- Vaccinia, varicella, and other viral diseases of the cornea and conjunctiva
- Mycobacterial infection of the eye
- Fungal diseases of the ocular structures
- Untreated parasitic eye infections
Drug Interactions
- Concurrent use of topical NSAIDs may increase the potential for corneal healing problems.
- CYP3A4 inhibitors (e.g., ritonavir, cobicistat) may increase dexamethasone levels.
Pregnancy and Breastfeeding
- Pregnancy: Tobramycin crosses the placenta. Dexamethasone use during pregnancy has been associated with intrauterine growth retardation. Use only if the potential benefit outweighs the potential risk.
- Breastfeeding: Tobramycin is excreted in human milk. It is unknown if dexamethasone is excreted. Exercise caution when administering to breastfeeding mothers.
Drug Profile Summary
- Mechanism of Action: Tobramycin: Inhibits bacterial protein synthesis. Dexamethasone: Suppresses inflammation. Hydroxypropyl methylcellulose: Lubricates the eye.
- Side Effects: Eye irritation, burning/stinging, itching, redness. Rarely, allergic reactions, increased intraocular pressure, glaucoma, cataract formation.
- Contraindications: Hypersensitivity, herpes simplex keratitis, viral or fungal eye infections, mycobacterial eye infections.
- Drug Interactions: Topical NSAIDs, CYP3A4 inhibitors.
- Pregnancy & Breastfeeding: Use with caution.
- Dosage: See detailed section above.
- Monitoring Parameters: Intraocular pressure, especially in patients with glaucoma or diabetes.
Popular Combinations
Tobramycin/dexamethasone is often used alone. Additional lubricants can be used concurrently if needed.
Precautions
- Monitor intraocular pressure.
- Do not discontinue therapy prematurely.
- Contact lens wearers should remove lenses before administration and wait 15 minutes before reinsertion.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Dexamethasone + Hydroxypropylmethylcellulose + Tobramycin?
A: See detailed Dosage section above.
Q2: What are the common side effects?
A: Common side effects include eye irritation, burning or stinging, itching, and redness.
Q3: Is it safe to use during pregnancy?
A: Use only if the potential benefit justifies the potential risk to the fetus.
Q4: Can I use this while breastfeeding?
A: Exercise caution. It is unknown if dexamethasone is excreted in breast milk, but tobramycin is.
Q5: What are the contraindications?
A: Contraindications include hypersensitivity, herpes simplex keratitis, viral or fungal eye infections, mycobacterial eye infections.
Q6: How does this combination work?
A: Tobramycin kills bacteria, dexamethasone reduces inflammation, and hydroxypropylmethylcellulose lubricates the eye.
Q7: Are there any drug interactions?
A: Concurrent use of topical NSAIDs and CYP3A4 inhibitors can interact with this medication.
Q8: What should I monitor while a patient is on this medication?
A: Monitor intraocular pressure, especially in patients at risk for glaucoma.
A: Yes, but they should remove their contact lenses before instilling the drops/ointment and wait 15 minutes before reinserting them.
