Doxycycline: Uses, Dosage, Side Effects, and Precautions

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).