What are the precautions and dosing guidelines for tetracycline (tetracycline) therapy?

Tetracycline Precautions and Dosing Guidelines

Tetracycline should be dosed at 500 mg orally every 6 hours for adults and 10 mg/kg every 6 hours for children ≥8 years (not exceeding 500 mg/dose), with strict avoidance in children under 8 years of age and pregnant women due to permanent tooth discoloration and enamel hypoplasia. 1

Dosing Guidelines

Adults

• Standard dose: 500 mg orally every 6 hours 1
• For acne: 500 mg daily given in divided doses; decrease to maintenance dose of 125-500 mg daily after clinical improvement 1
• For cholera: 500 mg every 6 hours for 72 hours 1

Children (≥8 years)

• 10 mg/kg every 6 hours orally (maximum 500 mg/dose) 1
• Should NOT be used in children under 8 years of age unless other appropriate drugs are ineffective or contraindicated 1

Major Precautions and Contraindications

Absolute Contraindications

• Hypersensitivity to any tetracycline 1
• Children under 8 years of age (due to permanent tooth discoloration and enamel hypoplasia) 1, 2
• Pregnancy (Category D) 1
• Nursing mothers (tetracycline is distributed into breast milk) 1

Drug Interactions

1. Metal ion interactions:

   • Tetracyclines form chelates with polyvalent metallic cations (Fe+++, Fe++, Al+++, Mg++, Ca++) 3
   • Antacids containing aluminum, calcium, or magnesium can reduce absorption by 50-90% 3
   • Milk and dairy products significantly reduce absorption 3
   • Separate administration by at least 3 hours to prevent interaction 3

2. Other significant interactions:

   • Oral anticoagulants (increased effect) 1
   • Penicillins (antagonistic effect - avoid concurrent use) 4
   • Methoxyflurane (increased risk of nephrotoxicity) 1, 4
   • Hormonal contraceptives (reduced effectiveness) 1

Adverse Effects

Gastrointestinal

• Anorexia, nausea, epigastric distress, vomiting, diarrhea 1
• Glossitis, black hairy tongue, dysphagia 1
• Enterocolitis, inflammatory lesions with Candidal overgrowth 1

Dental/Oral

• Permanent tooth discoloration during tooth development 1, 2
• Enamel hypoplasia 1, 2
• Prevalence of tetracycline staining is 3-6% 2

Skin

• Photosensitivity reactions 1, 4
• Maculopapular and erythematous rashes 1
• Exfoliative dermatitis 1

Other Important Adverse Effects

• Hepatotoxicity and liver failure 1
• Renal effects: rise in BUN (dose-related) 1
• Hypersensitivity reactions including urticaria, angioedema, anaphylaxis 1
• Hematologic effects: hemolytic anemia, thrombocytopenia, neutropenia 1

Special Populations

Pregnancy

• Pregnancy Category D - contraindicated 1
• Can cause permanent tooth discoloration and enamel hypoplasia in developing fetus 1, 2

Pediatric Use

• Should not be used in children under 8 years of age 1
• Exception: life-threatening infections when benefits outweigh risks 1

Renal Impairment

• Unlike doxycycline, standard tetracycline requires dose adjustment in renal impairment 5

Clinical Pearls

1. Tetracycline should be taken on an empty stomach, 1 hour before or 2 hours after meals for optimal absorption 3

2. Avoid concurrent administration with:

   • Dairy products
   • Antacids
   • Iron supplements
   • Multivitamins containing minerals

3. For most effective therapy, maintain serum concentrations above 0.5-1.5 μg/ml 3

4. Tetracycline achieves higher concentrations in gingival fluid (4-8 μg/ml) than in blood (2-2.5 μg/ml), making it particularly useful for periodontal infections 4

5. Expired tetracycline should never be used as it can cause Fanconi syndrome (renal tubular damage)

6. Monitor for superinfections, especially oral and anogenital candidiasis during prolonged therapy 1