Oral Steroid Dosing for Hypersensitivity Pneumonitis
For acute nonfibrotic hypersensitivity pneumonitis, start prednisone at 40 mg daily for 8 weeks, based on the only randomized controlled trial in this condition. 1
Initial Dosing Strategy
The recommended starting dose depends on disease severity:
Standard dose (nonfibrotic HP): Prednisone 40 mg daily is supported by the only double-blind, placebo-controlled trial in acute nonfibrotic HP, which showed improvement in DLCO after 1 month of treatment. 1
High-dose therapy (severe disease/respiratory failure): Prednisone 1-2 mg/kg/day (typically 40-100 mg daily) should be used for patients with severe disease or respiratory failure. 2
Alternative dosing: Some protocols use 0.5 mg/kg/day for 1-2 weeks, then alternate days for 6-8 weeks before tapering by 5-10 mg every 2 weeks. 2
Treatment Duration and Tapering
Total treatment duration should be 6-12 months depending on clinical response. 2
Initial high-dose therapy (40-100 mg daily) should continue for 2-4 months, with gradual taper after initial response. 2
In observational studies, corticosteroid therapy was administered for a median of 6.5 months. 1, 2
Taper steroids by 5-10 mg every 2 weeks after the initial treatment period. 2
Monitor total serum IgE every 6-8 weeks as a marker of disease activity during tapering (though this is more established for ABPA than HP). 1
Critical Distinction: Fibrotic vs. Nonfibrotic Disease
Corticosteroids are significantly more effective in nonfibrotic HP than fibrotic HP, which fundamentally changes treatment expectations. 1, 3
Nonfibrotic HP Response:
- Corticosteroid treatment resulted in reversal from monthly FVC% decline of 0.35% to an FVC% increase of 0.84% (P < .01). 1
- Significant improvement in FEV1, FVC, six-minute walk test, and oximetry (all P < 0.001 to P < 0.05). 3
Fibrotic HP Response:
- No significant changes in FVC% (P = .96) or DLCO% (P = .59) with corticosteroids alone. 1
- Patients receiving prednisone had worse FVC% decline over 36 months compared to those who did not (10.0% vs 1.3%; P = .04). 1
- Still showed some improvement in FEV1, FVC, oximetry, and six-minute walk test (P < 0.01), but less than nonfibrotic patients. 3
Monitoring Response
Assess response using objective parameters after 3 months of therapy: 2
- Dyspnea scores
- Pulmonary function tests (FVC, DLCO)
- Chest imaging (HRCT)
If no improvement within 5-7 days, consider increasing the dose by 50-100%. 2
Steroid-Sparing Agents for Fibrotic or Refractory Disease
For fibrotic HP or patients requiring prolonged corticosteroid therapy, add mycophenolate mofetil or azathioprine as steroid-sparing agents. 1, 2, 4, 5
Mycophenolate mofetil or azathioprine improved DLCO by 4.2% at 1 year (P < .001) in chronic HP patients. 1, 4
These agents significantly reduced prednisolone dose from 16.2 ± 9.7 mg to 8.2 ± 4.2 mg daily (P = 0.002). 5
Prednisone-sparing therapy altered the slope of monthly FVC decline (0.7% vs 0.2%; P = 0.001) in fibrotic HP. 1
Critical Pitfalls and Caveats
Antigen avoidance is paramount and must be the first step—corticosteroids alone without antigen removal will fail. 2
The evidence shows that even with aggressive corticosteroid treatment, progressive fatal disease can occur if antigen exposure continues. 6
For hot tub lung specifically, complete avoidance of MAC antigen exposure is essential alongside corticosteroid therapy. 2
Consider PCP prophylaxis for patients receiving ≥20 mg prednisone for ≥4 weeks. 2
Long-term outcomes are disappointing: At 5 years after treatment in the randomized trial, there were no significant between-group differences for any lung function measure, suggesting that early benefits may not persist. 1
Failure to respond does not exclude the diagnosis: Response rates are highly variable, and lack of improvement is common in fibrotic HP regardless of therapy. 1
Pediatric Considerations
For children with nonfibrotic HP, monthly high-dose pulse methylprednisolone (median 15 monthly courses) showed significant improvement in all lung function measures at 3 and 6 months (P < .05), with 80% achieving normal HRCT scans. 1, 2