Tetracyclines
ATC code: J01AA02 (Doxycycline)
Binds the 30S ribosomal subunit and blocks aminoacyl-tRNA attachment to the A-site, inhibiting bacterial protein synthesis. Bacteriostatic. Broad spectrum: gram-positive and gram-negative organisms, atypical pathogens – Mycoplasma, Chlamydia, Legionella, and also Rickettsia, Borrelia burgdorferi, Treponema pallidum. Compared to tetracycline, it has better bioavailability and a longer half-life of 18-22 hours.
First line
First-line systemic antibiotic for moderate-to-severe acne per 2024 guidelines. Dose is 100 mg once or twice daily for 3 months. Sub-antimicrobial dose of 40 mg modified-release (not registered in Russia) reduces inflammation without antibiotic pressure. Always combine with a topical retinoid and/or benzoyl peroxide to prevent resistance.
First line
First-line for uncomplicated chlamydial infection alongside azithromycin. Doxycycline 100 mg twice daily for 7 days. Recent meta-analyses suggest a slight advantage over single-dose azithromycin in eradication rates. In men with chlamydial proctitis, doxycycline is preferred.
First line
Alternative to macrolides for atypical community-acquired pneumonia. Active against Mycoplasma pneumoniae, Chlamydophila pneumoniae, Legionella. Per /ATS 2019, doxycycline is an outpatient CAP monotherapy option in patients without comorbidities when a macrolide is not suitable. Dose is 100 mg twice daily.
First line
Drug of choice for Lyme disease per // 2020. For early localized disease (erythema migrans), prescribe 100 mg twice daily for 10-21 days. For early disseminated disease without CNS involvement, the same regimen for 14-21 days. Doxycycline is the only oral antibiotic effective in neuroborreliosis without meningitis.
FDA pregnancy categories were retired in 2015 under PLLR (historically category D). Tetracyclines cross the placenta and accumulate in fetal bones and teeth in the second and third trimesters. Avoided during pregnancy. In life-threatening rickettsial disease, doxycycline may be used in pregnancy after specialist consultation – benefit outweighs the theoretical risk.
Passes into breast milk in small amounts. Calcium in milk binds doxycycline, reducing its bioavailability to the infant. Per LactMed, short-term use is acceptable, but prolonged courses during breastfeeding are not recommended.
doxycycline is evaluated for the following indications with varying evidence strength: Community-acquired pneumonia (evidence tier A), Acne vulgaris (evidence tier A), Lyme disease (borreliosis) (evidence tier A). See the full indication matrix with dosing and citations above on this page.
Common side effects of doxycycline (≥ 1 in 100): Nausea, diarrhea, Photosensitivity, Esophagitis, esophageal ulceration (with improper administration), Vaginal candidiasis. See the Safety section for uncommon and serious reactions.
FDA pregnancy categories were retired in 2015 under PLLR (historically category D). Tetracyclines cross the placenta and accumulate in fetal bones and teeth in the second and third trimesters. Avoided during pregnancy. In life-threatening rickettsial disease, doxycycline may be used in pregnancy after specialist consultation – benefit outweighs the theoretical risk.
Passes into breast milk in small amounts. Calcium in milk binds doxycycline, reducing its bioavailability to the infant. Per LactMed, short-term use is acceptable, but prolonged courses during breastfeeding are not recommended.
doxycycline is contraindicated in: Long courses in children under 8 (short courses up to 21 days for rickettsial disease or neuroborreliosis are acceptable per AAP 2018); Pregnancy; Hypersensitivity to tetracyclines; Severe hepatic impairment. Full list in the Safety section.