A 28-year-old woman presents with mucopurulent cervical discharge, dysuria, and lower abdominal pain. Gram stain of cervical swab shows intracellular gram-negative diplococci. Nucleic acid amplification test (NAAT) confirms Chlamydia trachomatis. She is not pregnant and has no drug allergies. What is the drug of choice for treatment?

Explanation

## First-Line Treatment of Chlamydia trachomatis Urogenital Infection **Key Point:** Doxycycline 100 mg orally twice daily for 7 days is the gold-standard first-line agent for uncomplicated urogenital chlamydial infection in non-pregnant women and men. ### Mechanism & Rationale 1. Doxycycline is a tetracycline that inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit. 2. It achieves excellent intracellular and urogenital tissue concentrations, essential for targeting the obligate intracellular pathogen *Chlamydia trachomatis*. 3. High cure rates (>95%) with minimal resistance reported globally. ### Treatment Guidelines by Condition | Condition | First-Line | Alternative | Notes | |-----------|-----------|-------------|-------| | Uncomplicated urogenital (non-pregnant) | Doxycycline 100 mg BD × 7 days | Azithromycin 1 g SD | Doxycycline preferred; azithromycin if intolerant | | Pregnancy | Azithromycin 1 g SD | Amoxicillin 500 mg TDS × 7 days | Tetracyclines contraindicated | | Rectal/pharyngeal | Doxycycline 100 mg BD × 7 days | Azithromycin 1 g SD | Same as urogenital | | Neonatal conjunctivitis | Erythromycin ointment topical | Oral azithromycin if systemic needed | Tetracyclines contraindicated in neonates | | Lymphogranuloma venereum (LGV) | Doxycycline 100 mg BD × 21 days | Azithromycin (less effective) | Longer duration required | **High-Yield:** Partner notification and treatment are mandatory; sexual contacts within 60 days should be evaluated and treated empirically. **Clinical Pearl:** Test of cure is NOT routinely recommended after completion of therapy in uncomplicated infection; persistent symptoms warrant evaluation for reinfection or coinfection (e.g., *Neisseria gonorrhoeae*). ### Why Doxycycline is Preferred - Superior intracellular penetration compared to macrolides. - Excellent bioavailability and urogenital tissue levels. - Cost-effective and widely available. - Minimal emerging resistance. - Covers concurrent *Mycoplasma genitalium* (increasingly recognized co-pathogen). **Warning:** Doxycycline is contraindicated in pregnancy and children <8 years due to risk of tooth discoloration and enamel hypoplasia.