Usage
Dexamethasone + Tobramycin ophthalmic suspension/ointment is prescribed for steroid-responsive inflammatory ocular conditions where superficial bacterial ocular infection or a risk of infection exists. This includes conditions like blepharitis, conjunctivitis, and keratitis. It is effective against tobramycin-susceptible microorganisms, particularly Pseudomonas aeruginosa.
Pharmacological Classification:
- Tobramycin: Aminoglycoside antibiotic
- Dexamethasone: Corticosteroid
Mechanism of Action:
Tobramycin inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit, leading to bacterial cell death. Dexamethasone, a potent corticosteroid, exerts anti-inflammatory and immunosuppressive effects by modulating inflammatory mediators.
Alternate Names
TobraDex®, Tobrasone®
How It Works
Pharmacodynamics: Tobramycin disrupts bacterial protein synthesis. Dexamethasone suppresses the inflammatory cascade, reducing edema and inflammation.
Pharmacokinetics:
- Absorption: Following topical ocular administration, systemic absorption of both drugs is low.
- Metabolism: Dexamethasone is metabolized primarily in the liver. Tobramycin is not significantly metabolized.
- Elimination: Dexamethasone metabolites are excreted mainly in the urine. Tobramycin is primarily excreted unchanged in the urine.
Mode of Action: Tobramycin acts on the 30S ribosomal subunit of bacteria. Dexamethasone binds to glucocorticoid receptors in the cytoplasm, translocates to the nucleus, and modulates gene expression.
Receptor Binding, Enzyme Inhibition, or Neurotransmitter Modulation: Dexamethasone binds to glucocorticoid receptors. Tobramycin’s primary mechanism is not through enzyme inhibition or neurotransmitter modulation, but by interfering with ribosomal protein synthesis.
Elimination Pathways: Dexamethasone is eliminated via hepatic metabolism and renal excretion. Tobramycin is eliminated primarily through renal excretion.
Dosage
Standard Dosage
Adults: Instill 1-2 drops into the affected eye(s) every 4-6 hours. During the initial 24-48 hours, the dosage may be increased to 1 drop every 2 hours, and subsequently, the frequency can be gradually reduced as clinical signs improve. The maximum treatment duration should not exceed 24 days.
Children (2 years and older): Same as adult dose. Safety and efficacy in children younger than 2 years have not been established.
Special Cases:
- Elderly Patients: Dosage adjustments are generally not necessary.
- Patients with Renal Impairment: No specific dosage recommendations are available. Monitor renal function.
- Patients with Hepatic Dysfunction: No specific dosage recommendations are available. Monitor hepatic function.
- Patients with Comorbid Conditions: Close monitoring is advised, especially for patients with glaucoma, diabetes, or a history of herpes simplex.
Clinical Use Cases
The dosage for various clinical scenarios generally aligns with the standard dosage guidelines, with potential adjustments based on severity and response.
Dosage Adjustments:
Dose modification may be considered in patients with renal or hepatic impairment. Monitor for adverse effects and adjust accordingly.
Side Effects
Common Side Effects
Eye irritation, itching, stinging, burning, redness, blurred vision, eyelid swelling, sensitivity to light.
Rare but Serious Side Effects
Allergic reactions (rash, hives, swelling), increased intraocular pressure (IOP), glaucoma, cataract formation, secondary ocular infections (fungal), optic nerve damage, delayed wound healing, corneal or scleral thinning/perforation.
Long-Term Effects
Glaucoma, cataracts, optic nerve damage.
Adverse Drug Reactions (ADR)
Severe allergic reactions, significant IOP increase, vision changes.
Contraindications
Hypersensitivity to tobramycin, dexamethasone, or any component of the formulation; herpes simplex keratitis; vaccinia; varicella; mycobacterial eye infections; fungal eye infections; untreated purulent eye infections.
Drug Interactions
Clinically significant interactions with ophthalmic administration of tobramycin/dexamethasone are unlikely due to low systemic absorption. However, caution should be exercised with concomitant use of other ophthalmic medications, particularly anticholinergics that may increase IOP. Inform patients to separate administration by at least 5 minutes.
Pregnancy and Breastfeeding
Tobramycin and dexamethasone can cross the placenta. Use only if the potential benefit outweighs the potential risk to the fetus. Tobramycin is excreted in breast milk. While the amount of tobramycin and dexamethasone in breast milk after topical ocular application is likely low, caution is advised.
Drug Profile Summary
- Mechanism of Action: Tobramycin inhibits bacterial protein synthesis; dexamethasone suppresses inflammation.
- Side Effects: Common: Eye irritation, itching, redness. Serious: Increased IOP, glaucoma, cataracts, secondary infections.
- Contraindications: Hypersensitivity, herpes simplex keratitis, viral eye infections, fungal and mycobacterial eye infections.
- Drug Interactions: Minimal with topical use, but caution with anticholinergics.
- Pregnancy & Breastfeeding: Use with caution; weigh benefits against risks.
- Dosage: 1-2 drops every 4-6 hours, initially every 2 hours for the first 24-48 hrs. Maximum 24 days.
- Monitoring Parameters: IOP, visual acuity, signs of infection, adverse reactions.
Popular Combinations
While not a combination in the same formulation, a fixed dose combination of Tobramycin and Dexamethasone covers both bacterial infection and inflammation making other combinations usually unnecessary.
Precautions
- Monitor IOP, particularly in patients with glaucoma or at risk of developing glaucoma.
- Watch for signs of secondary infection.
- Evaluate for corneal or scleral thinning in patients with conditions predisposing to perforation.
- Use cautiously in patients with diabetes.
- Advise patients on proper administration technique.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Dexamethasone + Tobramycin ophthalmic suspension?
A: Instill 1-2 drops into the affected eye(s) every 4-6 hours. During the initial 24-48 hours, increase to 1 drop every 2 hours. Reduce frequency as symptoms improve, not exceeding 24 days total treatment.
Q2: Can I use Dexamethasone + Tobramycin if I have glaucoma?
A: Use with extreme caution and close IOP monitoring, as corticosteroids can exacerbate glaucoma.
Q3: What are the signs of a serious allergic reaction to this medication?
A: Severe rash, hives, facial swelling, difficulty breathing, or anaphylaxis require immediate medical attention.
A: Contact lens wear is generally not recommended during treatment of an ocular infection or inflammation.
Q5: What should I do if my symptoms don’t improve after a few days?
A: Consult an ophthalmologist to re-evaluate the diagnosis and treatment plan.
Q6: Can this medication be used in pregnant or breastfeeding women?
A: Use cautiously, weighing the benefits against the potential risks to the fetus/infant. Consult an obstetrician/gynecologist for guidance.
Q7: Can I use other eye drops while using Dexamethasone + Tobramycin?
A: Inform your doctor of all other medications you are using. If other eye drops are necessary, separate administration by at least 5 minutes.
Q8: What is the maximum duration I can use this medication?
A: Do not use for more than 24 days without further ophthalmologic evaluation. Prolonged use can increase the risk of adverse effects like glaucoma, cataracts, and secondary infections.
Q9: Are there any specific precautions for elderly patients?
A: While dosage adjustments aren’t usually required, closely monitor for adverse effects and concomitant medical conditions.
