Methylprednisolone / Intratympanic Dexamethasone

Mechanism

Pharmacological Class and Group

High concentration local intratympanic corticosteroid therapy. High potency synthetic glucocorticoids for direct administration into the middle ear.

Mechanism of Action

Intratympanic treatment is based on the penetration of corticosteroids through the membrane of the round window (RVM) into the perilymph of the scala tympani, achieving exceptionally high local concentrations that would not be achieved by ordinary systemic route:

Mechanism of Action in the Inner Ear and Organ of Corti

1. Passive Diffusion through the Round Window Membrane: The corticosteroid instilled in the middle ear crosses the three cellular layers of the MVR (external epithelium, connective tissue layer and internal endothelium) following the molecular concentration gradient.

2. Activation of Glucocorticoid Receptors (GR) in the Organ of Corti: It binds to GR receptors distributed in the hair cells of the organ of Corti, in the spiral ligament, the stria vascularis and the supporting cells of the membranous labyrinth.

3. Local Anti-inflammatory and Immunosuppressive Effects: Inhibits the expression of the enzyme cyclooxygenase-2 (COX-2) and matrix metalloproteinases that mediate acute inflammatory tissue damage.

4. Protection of Cochlear Microcirculation: Modulates the activity of epithelial sodium and potassium channels (ENaC) present in the stria vascularis, restoring endocochlear potential and cellular endolymphatic fluid homeostasis:

Restoration of Endocochlear Potential ( ≈ +80 mV) Recovery of conduction in hair cells

5. Blocking Ischemia and Apoptosis: Stops apoptosis of hair cells induced by oxidative stress, cytotoxic cytokines or local autoimmunity mediated by immune complexes.

Pharmacokinetics

High Resolution Pharmacokinetics

• Perilymph Concentrations: Intratympanic administration of methylprednisolone (40 mg/mL) or dexamethasone (4 mg/mL or higher) achieves levels in the inner ear that exceed by up to a factor of 100 to 1000 the levels achieved after equivalent conventional intravenous doses.
• Systemic Absorption: Negligible. A minimal fraction drains through the Eustachian tube into the nasopharynx, or is absorbed through the capillaries of the middle ear, without generating suppressing effects on the hypothalamic-pituitary-adrenal (HPA) axis.
• Perilymph Elimination: The clearance of perilymph follows first-order kinetics, with a local elimination half-life ranging between 2 and 4 hours for dexamethasone, requiring a protocol of repeated instillations to maintain continuous therapeutic levels during the critical phase of cochlear damage.

Indicators and dose

Clinical Indications and Off-Label Uses

• Idiopathic Sudden Sensorineural Hearing Loss (SHLH): As a first-line treatment of choice (in combination with systemic corticosteroid therapy) or as rescue (salvage) therapy after failure of the oral systemic route, ideally started in the first two to three weeks after the onset of symptoms.
• Refractory Menière's Disease: Control of disabling vertigo attacks in patients who do not respond to betahistine, restrictive diet or diuretics, preserving the remaining auditory function (non-ablative therapy).
• Autoimmune Labyrinthitis: Bilateral fluctuating loss of auditory or vestibular function secondary to systemic autoimmune diseases (e.g., Lupus, Wegener's, Cogan Syndrome).

Dosage and Clinical Adjustment

Optic Instillation Protocol in Consultation:

• Election Preparations:
  • Methylprednisolone Succinate: Concentration of 40 mg/mL.
  • Dexamethasone Sodium Phosphate: Minimum concentration of 4 mg/mL to 10 mg/mL.
• Instillation Volume: Approximately 0.4 mL to 0.6 mL (enough to fill the entire tympanic cavity of an adult after fine needle myringotomy in the posteroinferior or anteroinferior quadrant of the eardrum).
• Typical Scheme: An instillation session every 3 to 7 days, completing a total of 3 to 4 consecutive doses, reevaluating the hearing level using control tone audiometry.
• Patient Positioning: Supine with the affected ear tilted 45 degrees upward, avoiding swallowing or speaking for 20-30 minutes afterwards to prevent accelerated clearance of the solution through the Eustachian tube.

Security

Absolute and Relative Contraindications

Absolute Contraindications

• Hypersensitivity to the chosen corticosteroid or to the excipients of the ampoule (special care with solutions containing benzyl alcohol or neurotoxic preservatives).
• Active suppurative infection of the middle ear (acute or chronic suppurative otitis media).
• Active herpetic or viral infection of the outer or middle ear.

Relative Contraindications

• Pre-existing large tympanic perforation not related to the procedure (may hinder drug retention in the middle ear, requiring the use of collagen sponges or carrier gels in the round window).

Adverse Effects (ADR) and Specific Toxicity

• Very common (>10%): Transient local pain or burning after instillation (more intense with methylprednisolone sodium succinate due to the osmolarity of the solution), transient rotatory vertigo induced by temperature difference in the ear canal or tympanic caloric stimulation.
• Common (1%-10%): Persistent tympanic perforation at the puncture site (occurs in approximately 1-3% of patients, usually resolving spontaneously; in rare cases requires myringoplasty).
• Uncommon (0.1%-1%): Middle ear infection (acute otitis media secondary to inoculation of skin bacteria), transient tinnitus or temporary worsening of hearing loss.

Procedure Alert: Avoid Ototoxic Excipients

Commercial glucocorticoid preparations intended for intramuscular or systemic use typically contain benzyl alcohol, sulfites, or propylene glycol as preservative agents or stabilizing vehicles. These compounds exhibit high direct cochlear toxicity on the hair cells of the organ of Corti and the stria vascularis. Only sterile solutions without preservatives should be used or dilution with saline solution should be optimized before intratympanic instillation.

Drug Interactions of Clinical Relevance

• No systemic interactions have been documented with oral or intravenous drugs due to the low plasma absorption rate of the local corticosteroid.
• Simultaneous instillation with topical otic anesthetics into the middle ear should be avoided, as they may interfere with the osmotic permeability of the round window membrane.

Safety in Pregnancy and Breastfeeding

• Pregnancy: Compatible. Unlike systemic oral corticosteroid therapy (which may be associated with a slight risk of cleft palate in the first trimester or oligohydramnios), the intratympanic route offers zero maternal plasma absorption, being an exceptionally safe alternative for the management of sudden hearing loss during pregnancy.
• Breastfeeding: Compatible. There is no risk of adrenal suppression or adverse reactions in the infant due to the lack of bioavailability of the drug in breast milk.