1. Clinical Overview
Dexamethasone is a potent, long-acting synthetic glucocorticoid with anti-inflammatory, immunosuppressive, anti-allergic, and anti-proliferative properties. It is approximately 25-30 times more potent than hydrocortisone. The 8mg strength is a high-dose formulation, primarily used for specific, severe conditions requiring intensive glucocorticoid therapy, such as cerebral edema, certain malignancies, and severe autoimmune flares.
| Onset | Duration | Bioavailability |
|---|---|---|
| Oral: 1-2 hours; Intravenous: Rapid, within minutes for some effects (e.g., anti-emetic). | Long-acting: 36 to 72 hours due to its long biological half-life. | Oral: Approximately 70-80%. |
2. Mechanism of Action
Dexamethasone binds to the cytosolic glucocorticoid receptor (GR), forming a complex that translocates to the nucleus. This complex binds to Glucocorticoid Response Elements (GREs) in DNA, leading to upregulation of anti-inflammatory proteins (transactivation) and repression of genes for pro-inflammatory cytokines (transrepression). It inhibits the transcription of genes for cytokines (IL-1, IL-2, IL-6, TNF-α), enzymes (COX-2, iNOS), and adhesion molecules.
3. Indications & Uses
- Cerebral edema (tumor-associated or post-operative)
- Severe allergic conditions (anaphylaxis, angioedema) unresponsive to conventional therapy
- High-altitude cerebral edema (HACE)
- As part of anti-emetic prophylaxis in highly emetogenic chemotherapy (e.g., with aprepitant/neurokinin-1 antagonist)
- Anti-inflammatory/immunosuppressive therapy for severe autoimmune diseases (e.g., SLE flare, pemphigus vulgaris)
- Adjunctive therapy in bacterial meningitis (to reduce neurological sequelae, especially in pneumococcal meningitis)
4. Dosage & Administration
Adult Dosage: Varies widely by indication. For cerebral edema: Initial loading dose of 10mg IV, then 4mg IV/IM/orally every 6 hours, tapered over days. For anti-inflammatory/immunosuppressive: 0.75 to 9 mg/day in divided doses. The 8mg tablet is used for specific high-dose protocols (e.g., once daily in chemotherapy, or in divided doses for severe conditions).
Administration: Oral: Take with or immediately after food to minimize GI upset. Do not crush or chew unless advised. For once-daily dosing, take in the morning to mimic circadian rhythm and reduce insomnia. Do not stop abruptly; taper gradually under medical supervision.
5. Side Effects
Common side effects may include:
- Insomnia
- Increased appetite, weight gain
- Fluid retention, edema
- Mood swings, nervousness
- Dyspepsia, heartburn
- Hyperglycemia
- Cushingoid habitus (moon face, buffalo hump) with prolonged use
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Warfarin/Anticoagulants | Dexamethasone may alter anticoagulant response (increase or decrease INR); monitor closely. | Major |
| Antidiabetics (Insulin, Metformin, Sulfonylureas) | Dexamethasone causes hyperglycemia; may require increased antidiabetic dose. | Major |
| NSAIDs (e.g., Ibuprofen, Diclofenac) | Increased risk of GI ulceration and bleeding. | Major |
| Diuretics (e.g., Furosemide, Hydrochlorothiazide) | Enhanced potassium loss, risk of severe hypokalemia. | Major |
| Phenytoin, Phenobarbital, Rifampicin | Induce CYP3A4, increasing dexamethasone metabolism, reducing its efficacy. | Moderate |
| Ketoconazole, Itraconazole, Clarithromycin | Inhibit CYP3A4, decreasing dexamethasone metabolism, increasing toxicity risk. | Moderate |
| Live Vaccines (MMR, Varicella, OPV) | Risk of disseminated infection; avoid vaccination during therapy. | Major |
| Digoxin | Hypokalemia induced by dexamethasone increases risk of digoxin toxicity. | Moderate |
7. Patient Counselling
- DO take exactly as prescribed; do not increase/decrease dose or stop suddenly.
- DO take with food or milk to avoid stomach upset.
- DO inform all doctors and dentists you are taking dexamethasone.
- DO carry a steroid alert card/bracelet.
- DON'T receive live vaccines without consulting your doctor.
- DON'T take over-the-counter NSAIDs (like ibuprofen) without asking your doctor.
- DON'T ignore signs of infection (fever, sore throat).
8. Toxicology & Storage
Overdose: Acute overdose can cause cushingoid symptoms, severe hyperglycemia, hypertension, fluid overload, psychosis, and acute adrenal insufficiency upon sudden withdrawal after chronic use.
Storage: Store below 30°C in a cool, dry place, protected from light and moisture. Keep out of reach of children. Do not use after the expiry date printed on the pack.