Methylprednisolone / Deflazacort

Mechanism

Pharmacological Class and Group

Systemic synthetic glucocorticoids of intermediate potency and short-intermediate action. Deflazacort is an oxazolin-derivative of prednisolone with less reported interference on bone and carbohydrate metabolism.

Mechanism of Action

They modulate the local immune response through direct interaction with cytoplasmic glucocorticoid receptors (GR-alpha), genomically regulating the expression of key proteins in inflammation and mucosal vascular homeostasis:

Systemic Transrepression and Transactivation Mechanism

1. Anti-inflammatory Transrepression Mechanism: The activated GR-alpha receptor physically inhibits the activity of the transcription factor NF-κB and activator protein 1 (AP-1). This stops transcription of mRNA for primary proinflammatory interleukins (IL-1, IL-2, IL-6, TNF-α), cell recruiting chemokines, and inflammatory isoenzymes such as inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2).

2. Transactivation Mechanism (Physiological Effects): Increases the expression of lipocortin-1 (annexin-1), which directly blocks the cellular activity of phospholipase A2, preventing the release of arachidonic acid and reducing the synthesis of inflammatory prostaglandins and chemotactic leukotrienes.

Glucocorticoid Transrepression of NF-κB ↓ Plasma exudation and laryngeal/facial edema

3. Restoration of Vascular Adrenergic Reactivity: Increases the density and sensitivity of beta-2 adrenergic receptors in the peripheral vasculature, enhancing spontaneous vasoconstriction and facilitating the resolution of massive obstructive edema.

Pharmacokinetics

High Resolution Pharmacokinetics

• Absorption and Bioavailability: Rapid and complete intestinal absorption for both compounds after oral intake. The bioavailability of methylprednisolone is 80-90%. Deflazacort is a prodrug that is rapidly hydrolyzed by intestinal plasma esterases to its biologically active metabolite 21-desacetyldeflazacort, with a bioavailability of 100%.
• Distribution: Excellent systemic tissue penetration. They are moderately bound to circulating plasma proteins (mainly albumin; methylprednisolone shows 77% protein binding).
• Metabolism: Selective hepatic oxidative metabolism mediated mainly by cytochrome CYP450 isoenzymes, in particular by CYP3A4.
• Excretion: Predominant renal excretion (conjugated and inactive drugs recovered in urine).
• Half-life (t_1/2): Short plasma half-life (1.8 to 3 hours for methylprednisolone), but they have an intermediate tissue biological half-life of 12 to 36 hours, allowing single daily doses.

Indicators and dose

Clinical Indications and Off-Label Uses

• Idiopathic Peripheral Facial Palsy (Bell's Palsy): Mandatory first-line systemic therapy, preferably initiated within the first 72 hours to reduce endoneural edema of the facial nerve within the temporal bone fallopian canal.
• Ramsay Hunt Syndrome (Otic Herpes Zoster): Adjuvant treatment to reduce acute neuritis and prevent permanent paralysis, in mandatory combination with systemic antivirals (Acyclovir/Valacyclovir).
• Idiopathic Sudden Sensorineural Hearing Loss (SNHL): Immediate oral shock scheme to rescue the function of the hair cells of the membranous labyrinth.
• Acute Laryngeal or Subglottic Edema: Prophylactic treatment before or after extubation in intensive care units, or in acute cases of severe stridulous laryngitis.

Dosage and Clinical Adjustment

Bell's Facial Palsy Scheme (Adults):

• Methylprednisolone: Start with 1 mg/kg/day orally (usually 60 mg to 80 mg per day given in the morning with breakfast) for 5 to 7 days, followed by a progressive taper over the next 5 to 7 days (usual total dose of 10 days).
• Deflazacort (Approximate equivalent dose of 0.75 mg dexamethasone ≈ 4 mg methylprednisolone ≈ 6 mg deflazacort): Start with 90 mg to 120 mg orally once daily in the morning with similar progressive taper.

Scheme for Stridulous Laryngitis / Croup (Pediatrics):

• IV methylprednisolone (Emergency): 1 mg/kg to 2 mg/kg slowly intravenously every 6 or 8 hours in acute phases of respiratory distress.

Adjustment in Renal or Liver Failure:

• Dose adjustment is not required in renal failure.
• In patients with Child-Pugh C end-stage liver failure, it is preferred to use methylprednisolone (it is the direct active form) rather than deflazacort (requires esterase hepatic activation), reducing the maintenance dose by 25-50% to prevent accelerated Cushing's.

Security

Absolute and Relative Contraindications

Absolute Contraindications

• Known hypersensitivity to the corticosteroid or the excipients of the formulation.
• Active systemic fungal infections without optimal basic treatment.
• Concomitant administration of live attenuated virus vaccines in patients receiving immunosuppressive doses of glucocorticoids.

Relative Contraindications

• Decompensated or unstable diabetes mellitus (powerful hyperglycemic effect).
• Severe uncontrolled high blood pressure or congestive heart failure.
• Active peptic ulcer with risk of upper digestive perforation.
• Active or latent pulmonary tuberculosis without optimal chemoprophylaxis.

Adverse Effects (ADR) and Specific Toxicity

• Common (1%-10%): Dose-dependent hyperglycemia (due to stimulation of de novo hepatic gluconeogenesis and transient insulin resistance), sleep insomnia, irritability, increased fluid retention with peripheral edema, dyspepsia, proximal muscle weakness.
• Uncommon (0.1%-1%): Osteoporosis (in prolonged use >3 weeks), increased risk of opportunistic infections, myopathy due to corticosteroids, delayed bone and intestinal healing.
• Very rare (<0.01%): Acute adrenal insufficiency due to sudden suppression of cortisol secretion from the hypothalamic-pituitary-adrenal axis, avascular necrosis of the femoral head.

Tampering Alert: Mandatory Progressive Withdrawal ("Tapering")

The uninterrupted use of systemic corticosteroids at supraphysiological doses for more than 14-21 consecutive days produces transient atrophy due to lack of trophic stimulation of the fasciculated zone of the adrenal cortex. Abrupt withdrawal of treatment, or failure to increase the dose in the face of major surgical or infectious stress, can trigger a potentially fatal acute adrenal crisis, characterized by refractory cardiovascular collapse, severe hyponatremia, and hyperkalemia. It is mandatory to establish a strict protocol of progressive dose reduction ("tapering") before stopping therapy.

Drug Interactions of Clinical Relevance

• Non-Steroidal Anti-Inflammatories (NSAIDs) or Salicylates: Destructive pharmacodynamic synergism on the mucosal barrier of the stomach, multiplying the risk of bleeding peptic ulcers.
• Inducers of the liver enzyme CYP3A4 (Rifampin, Phenytoin, Carbamazepine): They notably accelerate the metabolic clearance of corticosteroids, markedly decreasing their anti-inflammatory therapeutic effect in facial paralysis or laryngitis.
• Oral antidiabetics or Insulin: They significantly reduce their hypoglycemic effectiveness due to the hyperglycemic effect of glucocorticoids. Requires temporary insulin adjustment.

Safety in Pregnancy and Breastfeeding

• Pregnancy: Compatible with caution. Methylprednisolone is efficiently inactivated by the fetal placental enzyme 11-β-hydroxysteroid dehydrogenase type 2 (11β-HSD2), protecting the developing fetus from maternal hormonal surges. It is preferred over dexamethasone in pregnant women with facial paralysis to avoid direct systemic fetal exposure.
• Breastfeeding: Compatible. They are excreted in breast milk in extremely low quantities after oral dosing, and it is considered safe to space breastfeeding about 4 hours after taking.