A 46‑year‑old man with untreated HIV infection (CD4 = 180 cells/ยตL, HIV RNA = 75 000 copies/mL) is brought to the emergency department because of progressive memory loss, gait unsteadiness, and bilateral lower‑limb weakness over two months. He reports intermittent headaches and blurred vision.
Vitals: T 37.4 °C, BP 126/72 mm Hg, HR 88 bpm.
Neuro exam: wide‑based gait, positive Romberg, brisk patellar reflexes; pupils accommodate but are sluggish to light.
Serum RPR: reactive 1 : 128 (prior documentation six months ago: non‑reactive).
CSF: WBC 95 cells/ยตL (90 % lymphs), protein 110 mg/dL, VDRL reactive 1 : 16.
Question
Which antibiotic regimen is most appropriate to treat this patient’s infection?
A) Aqueous crystalline penicillin G 3 million units IV every 4 h for 14 days
B) Meropenem 2 g IV every 8 h for 14 days
C) Doxycycline 200 mg orally twice daily for 28 days
D) Ceftriaxone 2 g IV once daily for 14 days
E) Levofloxacin 750 mg IV once daily for 14 days
CORRECT ANSWER
A) Aqueous crystalline penicillin G 3 million units IV q4h × 14 d
WHY OPTION A IS BEST
Penicillin G is the CDC and WHO first‑line therapy for neurosyphilis.
Achieves treponemicidal CSF concentrations; proven cure rates in both immunocompetent and HIV‑positive patients.
Ten‑to‑fourteen‑day IV course eradicates treponemes and prevents progression.
RATIONALE FOR OTHER OPTIONS
B) Meropenem: Active against many Gram‑negative bacteria but has no demonstrated efficacy against Treponema pallidum; not recommended in any guideline for syphilis.
C) Doxycycline: Accepted oral alternative for early uncomplicated syphilis when penicillin cannot be used, but CSF penetration and clinical data for neurosyphilis are inadequate.
D) Ceftriaxone: Has good CSF penetration and some evidence of effectiveness; used only when true penicillin allergy precludes desensitisation. Penicillin remains superior.
E) Levofloxacin: Fluoroquinolones lack activity against T. pallidum and have no role in syphilis management.
KEY TAKE‑HOME POINTS
Penicillin G IV is the gold standard for neurosyphilis.
Ceftriaxone is a reasonable fallback after careful allergy assessment; desensitise and use penicillin whenever possible.
Oral doxycycline, carbapenems, and fluoroquinolones do not reliably cure neurosyphilis and should be avoided.
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