What steroid dose and taper schedule should be used for an adult with acute or sub‑acute hypersensitivity pneumonitis?

Steroid Dosing for Hypersensitivity Pneumonitis

For acute or subacute hypersensitivity pneumonitis in adults, initiate prednisone at 0.5 mg/kg/day for 2-4 weeks, then taper over a total duration of 4 months. 1, 2

Initial Dosing Strategy

Start with prednisone 0.5 mg/kg/day (typically 30-40 mg daily for average-sized adults) for the first 2-4 weeks. 1, 2 This dose provides adequate anti-inflammatory effect while minimizing adverse events compared to higher-dose protocols. 1

• A landmark trial comparing low-dose (0.5 mg/kg/day) versus high-dose (0.75 mg/kg/day) protocols found similar exacerbation rates but fewer adverse events with the lower dose, though initial response at 6 weeks was slightly slower. 1
• For severe presentations with respiratory failure, escalate to 1-2 mg/kg/day. 1

Tapering Schedule

After the initial 2-4 weeks at 0.5 mg/kg/day, reduce by 5 mg weekly until reaching 10 mg/day, then slow the taper to 1 mg reductions every 4 weeks until discontinuation at 4 months total duration. 2, 3

• The 4-month total duration balances efficacy with minimizing steroid-related complications. 1
• Some centers use an intermediate approach: 0.5 mg/kg/day for 4 weeks, then 0.25 mg/kg/day for 4 weeks, then 0.125 mg/kg/day for 4 weeks, followed by 5 mg reductions every 2 weeks. 1
• For subacute or chronic fibrotic HP requiring longer treatment (months), maintain closer monitoring and slower tapers. 4, 5

Critical Decision Points

Antigen avoidance is paramount and must occur before or concurrent with steroid initiation—steroids alone without antigen removal will fail. 1, 4

• If symptoms persist despite adequate antigen avoidance and 4-8 weeks of steroids, consider adding steroid-sparing agents (mycophenolate mofetil 1000 mg twice daily or azathioprine). 6
• Oral itraconazole (200 mg twice daily for 4 months) can be used as an alternative to steroids in patients who cannot tolerate corticosteroids, though onset of action is slower. 1

Radiological Pattern Considerations

Non-fibrotic HP (ground-glass opacities, mosaic attenuation, centrilobular nodules) responds significantly better to corticosteroids than fibrotic HP, but both patterns show measurable improvement. 7

• Non-fibrotic patterns show significant improvement in FEV1, FVC, 6-minute walk distance, and oxygen saturation after 8 weeks of methylprednisolone 0.5 mg/kg/day. 7
• Fibrotic patterns (reticulation, traction bronchiectasis, honeycombing) still demonstrate improvement in FVC, oxygen saturation, and 6-minute walk distance, though less pronounced than non-fibrotic disease. 7, 5
• The presence of isolated giant cells, poorly formed granulomas, or peribronchiolar fibrosis on biopsy helps distinguish chronic HP from usual interstitial pneumonia, and these patients may still respond to steroids despite extensive fibrosis. 5

Essential Supportive Measures

All patients receiving steroids for HP require prophylaxis and monitoring:

• Start proton pump inhibitor for gastrointestinal protection. 3, 8
• Initiate calcium (1000-1500 mg daily) and vitamin D (800-1000 IU daily) supplementation. 3, 8
• For treatment duration ≥4 weeks at ≥20 mg prednisone equivalent, add Pneumocystis jiroveci pneumonia prophylaxis with trimethoprim-sulfamethoxazole. 3, 8
• Monitor fasting glucose weekly for the first month, then monthly. 3

Managing Treatment Failure or Relapse

If disease flares during tapering, immediately return to the pre-relapse dose and maintain for 4-8 weeks before attempting a slower taper. 2

• Steroid-refractory acute HP (no improvement after 48-72 hours of high-dose steroids) may require addition of cyclosporin A or other immunosuppressive agents. 9
• For chronic HP requiring prolonged steroids, mycophenolate mofetil or azathioprine can reduce prednisolone dose by approximately 50% (from 16 mg to 8 mg daily) while stabilizing or improving lung function. 6

Critical Pitfalls to Avoid

Never taper faster than 5 mg weekly above 10 mg/day or faster than 1 mg every 4 weeks below 10 mg/day—rapid tapering causes disease flare and symptomatic adrenal insufficiency. 2

• HPA axis suppression occurs with any dose >7.5 mg daily for >3 weeks and may persist 6-12 months after discontinuation. 2
• Provide stress-dosing education: double the current dose for 3 days during minor illness, or use hydrocortisone 50 mg IV every 8 hours for major surgery/severe illness. 2
• Check 8 AM cortisol after 48 hours off prednisone once tapered to ≤5 mg/day; normal should be >10 mcg/dL (ideally >15-20 mcg/dL). 2
• Failing to remove the inciting antigen renders steroid therapy ineffective—detailed environmental exposure history is the most critical diagnostic and therapeutic tool. 4

Special Populations

For hot-tub lung (MAC-related hypersensitivity pneumonitis), use prednisone 1-2 mg/kg/day tapered over 4-8 weeks for severe disease or respiratory failure, combined with complete avoidance of indoor hot tub exposure. 1

• Consider adding antimycobacterial therapy (clarithromycin, rifampin, ethambutol) for immunocompromised patients or those with persistent disease after antigen removal, though shorter courses (3-6 months) may suffice. 1