Tetracycline
Tetracycline
Generic Name
Tetracycline
Mechanism
Tetracycline is a broad‑spectrum glycycline that inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit.
• Prevents attachment of aminoacyl‑tRNA to the A‑site, blocking peptide elongation.
• Acts bacteriostatic against most Gram‑positive and Gram‑negative organisms; in high concentrations it can become bactericidal.
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Pharmacokinetics
- Absorption: Oral bioavailability ~80 % when taken on an empty stomach; food reduces uptake.
- Distribution: Extensive tissue penetration; achieves high concentrations in skin, lungs, bone, and the CNS. Accumulates in teeth and bone—requires caution in children and pregnant females.
- Metabolism: Minimal hepatic metabolism; largely unchanged in plasma.
- Elimination: Primarily renal (≈90 %); half‑life ~8–10 h (oral).
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Indications
| Indication | Typical Use |
| Acne vulgaris | Oral or topical formulations |
| Chlamydia trachomatis | STD treatment |
| Rickettsial diseases (e.g., Rocky Mountain spotted fever) | Empiric therapy |
| Anthrax (post‑exposure) | Secondary prophylaxis |
| Syphilis (early stages) | Alternative to penicillin in limited settings |
| Brucellosis | Combination therapy |
| Typhoid fever | Augmentation of fluoroquinolone/azithromycin therapy |
| COVID‑19–associated bacterial pneumonia (off‑label in some settings) | Adjunctive antibacterial coverage |
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Contraindications
- Allergy to tetracyclines.
- Pregnancy (3rd trimester) and lactation – due to risk of permanent tooth discoloration and inhibition of bone growth.
- Children < 8 y – teeth & bone safety concerns.
- Renal impairment – dose adjustment required.
- Concurrent use of antacids, iron, or calcium supplements – modulate absorption.
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Dosing
- Adults: 500 mg PO twice daily or 250 mg PO every 6 h.
- Children (8–12 y): 15 mg/kg PO BID.
- Special Populations: Reduce dose or dosing interval in CKD stage 3–4.
- Administration tips
- Take on an empty stomach, at least 1 h before/after food.
- Use a long‑tapered, high‑dose regimen to reduce GI irritation.
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Adverse Effects
| Common (≤10 %) | Serious (≤1 %) |
| Gastro‑intestinal upset (N/S, dyspepsia) | Hepatotoxicity (elevated LFTs, jaundice) |
| Photosensitivity rash | Hypersensitivity reactions (angioedema, anaphylaxis) |
| Tooth discoloration (in kids) | Osteomyelitis (rare, but inheritable in osteogenesis imperfecta) |
| Vaginal candidiasis | Drug‑induced lupus‑like syndrome |
| ↑odour of urine (trimethylamine)** | Quinocromic red‑brown dyes in urine (benign) |
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Monitoring
- Baseline: CBC, CMP, urinalysis.
- During therapy:
- Check liver enzymes after 2–4 weeks if symptoms arise.
- Monitor kidney function in patients with creatinine clearance <60 mL/min.
- Special Settings:
- Monitor skin/eye exposure for UV‑related adverse events.
- In pregnancy, counsel on dental guidance and consider alternative agents.
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Clinical Pearls
- “Empty‑Stomach Rule”: Overnight fasting or two‑hour separation from meals maximizes absorption and decreases GI side‑effects.
- Avoid Antacids: Administer 2 h before or after calcium/iron/antacids; consider fast‑picking between dosing.
- Use Refined Formulations: Oral suspensions are better tolerated by children but require proper mixing to avoid dose inaccuracies.
- Photo‑Protection: Advise broad‑spectrum sunscreen, hats, and limiting outdoor activities during peak UV hours.
- Resistance Awareness: Overuse can select for resistant strains; use only when indicated, preferably for 7–10‑day courses.
- Topical vs. Systemic: For mild acne, topical 0.05–0.1 % doxycycline gels may lessen systemic toxicity.
- Drug‑Drug Interactions: Remember that sulfonamides can compete for renal excretion, raising tetracycline levels.
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