Doxycycline is a broad‑spectrum tetracycline antibiotic used for diverse bacterial and atypical infections.
Indications
- Respiratory: community‑acquired pneumonia, exacerbations of COPD/bronchitis (atypicals).
- STIs: Chlamydia, syphilis (alternative), LGV.
- Skin/soft tissue: Acne vulgaris (anti‑inflammatory + antimicrobial), rosacea, cellulitis (with other agents).
- Tick‑borne: Lyme disease (early), anaplasmosis, ehrlichiosis, RMSF.
- Malaria prophylaxis (chloroquine‑resistant areas).
- Anthrax, plague, tularemia (bioterrorism).
Dosing (Adults)
- Standard: 100 mg PO/IV q12h.
- Acne: 50–100 mg daily.
- Malaria prophylaxis: 100 mg daily (start 1–2 days before, continue 4 weeks after).
Key Adverse Effects
- GI: Nausea, vomiting, diarrhea, esophagitis (take with full glass water, remain upright 30 min).
- Photosensitivity (sunburn risk) – use SPF, protective clothing.
- Candidiasis (oral/vaginal).
- Tooth discoloration & enamel hypoplasia in children <8 yr and pregnancy (contraindicated).
- Intracranial hypertension (rare) – headache, visual changes.
Drug Interactions
- Antacids, Ca/Fe/Mg/Zn supplements, bismuth – chelation reduces absorption (separate by 2–3 hrs).
- Warfarin – enhanced anticoagulation (monitor INR).
- Oral contraceptives – theoretical reduced efficacy (backup recommended).
- Penicillins – bacteriostatic vs. bactericidal antagonism (avoid combination).
Special Populations
- Renal impairment: no dose adjustment (non‑renal elimination).
- Hepatic impairment: use caution.
- Pregnancy/lactation: contraindicated (Category D).
