A 42-year-old man presents to the clinic with a fever (39.2 °C), headache, and myalgias that began 5 days after hiking in North Carolina. He found an attached tick on his calf at the time. This morning he developed a petechial/maculopapular rash that started on his wrists and ankles and has begun spreading centrally. RMSF serologies are pending. Which management step is most appropriate now?

Question

Accepted Answer

✅ D. Start doxycycline 100 mg PO BID empirically now and continue until at least 3 days after fever resolves (≥ 5–7 days total)
Correct. Doxycycline is first-line treatment for RMSF in patients of all ages (including children) per CDC guidance. Treatment should be started empirically on clinical suspicion — classic triad of fever + headache + rash after tick exposure, with rash beginning on wrists/ankles and spreading centrally. Delay increases mortality significantly, so empiric doxycycline is the standard answer.

❌ A. Start azithromycin 500 mg PO × 1 then 250 mg daily × 4 days
Incorrect. Azithromycin is not the treatment for Rocky Mountain spotted fever. Delaying effective therapy is dangerous — RMSF mortality climbs sharply when treatment is delayed beyond day 5 of illness.

❌ B. Wait for RMSF serology results before starting any antibiotic
Incorrect. Treatment for RMSF must be empiric — antibody-based serologies are often negative in the first week and may lag clinical disease. Waiting for labs is associated with increased mortality.

❌ C. Start amoxicillin 500 mg PO TID × 14 days for presumed early Lyme disease
Incorrect. The epidemiology (NC), fever with headache, and rash starting on the wrists/ankles and spreading centrally are classic for RMSF, not Lyme. Amoxicillin does not reliably treat *Rickettsia rickettsii*.

Doxycycline

✅ Indications

⚙️ Mechanism of Action

📏 Dosing

🚫 Contraindications

⚠️ Adverse Effects

🔬 Monitoring

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