What is the recommended management for a patient with classic Congenital Adrenal Hyperplasia (CAH) transitioning from 10mg of dexamethasone (Decadron) daily, including dosing for hydrocortisone and fludrocortisone to avoid adrenal crisis?

Management of Classic CAH Transitioning from Dexamethasone to Physiologic Replacement

Transition immediately from dexamethasone 10mg daily to hydrocortisone 15-25 mg daily in divided doses (typically 10mg at 7:00 AM, 5mg at 12:00 PM, and 2.5-5mg at 4:00 PM) plus fludrocortisone 50-200 µg daily as a single morning dose to prevent adrenal crisis. 1

Critical Rationale for Immediate Transition

• Dexamethasone should be avoided in CAH management because it provides non-physiologic, prolonged suppression and increases risk of iatrogenic Cushing's syndrome 1
• The current 10mg dexamethasone dose is approximately equivalent to 200-250mg of hydrocortisone daily—a massively supraphysiologic dose causing significant glucocorticoid excess 1
• Immediate transition is safe because the patient has been chronically suppressed and will not experience withdrawal if switched directly to appropriate physiologic dosing 1

Specific Hydrocortisone Dosing Protocol

Standard three-dose regimen (preferred): 1

• 10mg at 7:00 AM (upon awakening)
• 5mg at 12:00 PM (±1 hour)
• 2.5-5mg at 4:00 PM (±1 hour, but no later than 6 hours before bedtime)
• Total daily dose: 17.5-20mg

Alternative regimens if three-dose schedule is impractical: 1

• Two-dose: 15mg at 7:00 AM + 5mg at 12:00 PM
• Two-dose: 10mg at 7:00 AM + 10mg at 12:00 PM
• Three-dose: 15mg + 5mg + 5mg

For patients with compliance issues or marked energy fluctuations, consider prednisolone 4-5mg as single morning dose instead (equivalent to approximately 20-25mg hydrocortisone), though this is second-line 2, 3

Essential Fludrocortisone Dosing

Start fludrocortisone 100 µg (0.1mg) once daily upon awakening 1

• Typical dose range: 50-200 µg daily for adults 1
• Higher doses (up to 500 µg) may be needed in younger adults or during pregnancy 1
• Critical point: Under-replacement of mineralocorticoid is common and predisposes to recurrent adrenal crises 1, 4
• Do not compensate for mineralocorticoid under-replacement by increasing glucocorticoid dose, as this causes iatrogenic Cushing's while still risking crisis 2

Monitoring Parameters to Prevent Adrenal Crisis

Clinical assessment (most important): 1, 4

• Blood pressure supine and standing (orthostatic hypotension indicates under-replacement)
• Salt cravings (indicates mineralocorticoid insufficiency)
• Weight stability
• Absence of morning nausea/poor appetite
• Normal energy throughout day

Laboratory monitoring: 1, 4

• Serum sodium and potassium (hyponatremia/hyperkalemia indicate under-replacement)
• Plasma renin activity (target upper half of reference range for optimal mineralocorticoid replacement)
• Morning cortisol day curve (0,2,4,6 hours post-dose) if absorption issues suspected

Dose Titration Strategy

Adjust fludrocortisone by 50 µg increments based on: 1, 4

• Persistent orthostatic hypotension → increase dose
• Salt cravings despite adequate sodium intake → increase dose
• Hypertension or peripheral edema → decrease dose (but never discontinue completely)
• Hyponatremia or hyperkalemia → increase dose

Adjust hydrocortisone based on: 1

• Persistent fatigue, nausea, weight loss → increase dose
• Weight gain, insomnia, cushingoid features → decrease dose
• Rapid cortisol disappearance on day curve → increase dosing frequency

Critical Education to Prevent Adrenal Crisis

Stress dosing protocol (mandatory patient education): 1, 3

• Minor illness/fever: Double or triple hydrocortisone dose for 2-3 days
• Vomiting/unable to take oral medications: Emergency IM hydrocortisone 100mg and immediate medical attention
• Major stress/surgery: IV hydrocortisone 100mg bolus, then 100-300mg/day continuous infusion or divided every 6 hours 1

Essential patient supplies: 1, 3

• Emergency injectable hydrocortisone 100mg IM kit
• Medical alert bracelet stating "adrenal insufficiency"
• Written sick-day management plan

Medication Interactions Requiring Dose Adjustment

Medications that increase hydrocortisone requirements: 1, 3

• Anti-epileptics (phenytoin, carbamazepine, phenobarbital)
• Rifampin and other antituberculosis drugs
• Topiramate
• Etomidate

Medications that decrease requirements (avoid or adjust): 1, 3

• Grapefruit juice
• Licorice/carbenoxolone

Medications that interact with fludrocortisone (avoid): 1, 4

• Diuretics
• Acetazolamide
• NSAIDs
• Drospirenone-containing contraceptives (may require increased fludrocortisone)

Special Considerations for CAH

• Encourage unrestricted sodium intake and avoid potassium-containing salt substitutes 1
• If morning nausea persists, patient can take first hydrocortisone dose 30-60 minutes earlier, then return to sleep 1
• Mineralocorticoid replacement must be restarted when hydrocortisone dose falls below 50mg/day during any stress-dose tapering 1
• Tablets can be stored at room temperature despite package labeling requiring refrigeration (decay rate only 0.1% in 6 months) 1

Common Pitfalls to Avoid

• Never use dexamethasone for chronic CAH management due to non-physiologic suppression and Cushing's risk 1
• Never omit fludrocortisone in classic CAH (salt-wasting form requires mineralocorticoid replacement) 1
• Never take last hydrocortisone dose within 6 hours of bedtime to avoid insomnia 2
• Never discontinue fludrocortisone completely even if blood pressure is elevated; reduce dose instead 4
• Never delay emergency treatment if patient cannot take oral medications—administer IM hydrocortisone 100mg immediately 1