A 35-year-old HIV-positive man (CD4 45/µL, viral load 120,000 copies/mL) develops bilateral diffuse interstitial infiltrates, progressive hypoxia (PaO₂ 56 mmHg on room air), and an elevated serum LDH. BAL shows Pneumocystis jirovecii. What is the treatment and the indication for adjunctive corticosteroids?

• A TMP-SMX; adjunctive prednisone if room air PaO₂ <70 mmHg or A-a gradient >35 mmHg ✓
• B TMP-SMX; corticosteroids are contraindicated in PCP (immunosuppressed patient)
• C Pentamidine IV; adjunctive prednisone only if CD4 <50
• D TMP-SMX + caspofungin for 21 days; no steroids needed

Explanation

TMP-SMX (trimethoprim 15-20 mg/kg/day + sulfamethoxazole 75-100 mg/kg/day) is first-line treatment for PCP (21 days). Adjunctive corticosteroids (prednisone 40 mg BD for 5 days, then tapering over 21 days) are strongly indicated when room air PaO₂ <70 mmHg or alveolar-arterial (A-a) gradient >35 mmHg — they reduce the inflammatory flare triggered by dying Pneumocystis organisms and have been shown to reduce mortality (NEJM 1990 landmark trial). This patient's PaO₂ of 56 mmHg meets this criterion. Pentamidine is second-line. Caspofungin has no role in PCP.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.