| Class |
Tetracycline‑class broad‑spectrum antibiotic |
| Mechanism |
Binds the 30S ribosomal subunit → inhibits protein synthesis |
| Indications |
• Community‑acquired bacterial infections (e.g., respiratory, urinary, skin)
• Acne vulgaris
• Tick‑borne diseases (Lyme, ehrlichiosis, anaplasmosis)
• Malaria prophylaxis (in certain regions)
• Certain sexually transmitted infections (e.g., Chlamydia trachomatis)
• Travel‑related infections (e.g., Rickettsia spp.) |
| Typical adult dose |
• Infections: 100 mg twice daily (every 12 h) for 7–14 days (may extend up to 4–6 weeks depending on the infection).
• Acne: 100 mg once daily (often at bedtime) for 3–6 months.
• Tick‑borne diseases: 100 mg twice daily for 14–21 days (or longer for complicated Lyme disease). |
| Special populations |
• Children < 8 yr: contraindicated (teeth discoloration & bone growth interference).
• Pregnancy: Category D – avoid unless no alternatives.
• Breastfeeding: excreted into milk; usually avoided.
• Renal impairment: dose adjustment often required (e.g., 50 mg BID or 100 mg q48h).
• Hepatic impairment: generally safe; monitor for other antibiotics that need dose reduction. |
| Administration |
• Take with a full glass of water to reduce esophageal irritation.
• Preferably on an empty stomach (1 h before or 2 h after meals).
• Avoid dairy products, calcium‑fortified juices, antacids, iron, or zinc supplements for at least 2 h before/after dosing (they chelate doxycycline and reduce absorption). |
| Common side effects |
• Gastro‑intestinal upset (nausea, diarrhea, dyspepsia)
• Photosensitivity (sunburn risk) – wear sunscreen/long sleeves
• Oral thrush, esophagitis if taken improperly
• Rare: tendonitis/tendon rupture (especially in elderly or those on steroids) |
| Serious but uncommon |
• Clostridioides difficile colitis
• Severe allergic reactions (rash, anaphylaxis)
• Secondary infections (candida) |
| Drug interactions |
• Antacids/Calcium, Iron, Magnesium – reduce absorption.
• Warfarin – may potentiate anticoagulation.
• Digoxin – increases serum levels.
• Other tetracyclines – additive toxicity.
• CYP3A4 inhibitors/inducers may alter metabolism (though doxycycline is largely excreted unchanged). |
| Contraindications |
• Known hypersensitivity to tetracyclines or any component
• Pregnancy & lactation
• Children under 8 yrs |
| Monitoring |
• For prolonged use (≥ 2 weeks) monitor for GI symptoms, photosensitivity, and, in elderly, tendon pain.
• In patients with renal insufficiency, consider dose adjustment. |
| Storage |
• Keep at room temperature (15–25 °C).
• Protect from moisture and light.
• Keep out of reach of children. |
| Patient counseling |
• Take with water; avoid lying down for 30 min to prevent esophageal irritation.
• Avoid sun exposure; use sunscreen SPF 30+ or cover up.
• Report any severe stomach upset, diarrhea, or signs of allergic reaction.
• Inform all healthcare providers (including dentists) of doxycycline use before procedures (some dental x‑rays may need adjustments). |