Tetracyclines – Uses, Effects & Side Effects
Tetracyclines are broad-spectrum antibiotics used to treat a wide range of bacterial infections. They work by inhibiting bacterial protein synthesis and are effective against both gram-positive and gram-negative pathogens.
Things worth knowing about "Tetracyclines"
Tetracyclines are broad-spectrum antibiotics used to treat a wide range of bacterial infections. They work by inhibiting bacterial protein synthesis and are effective against both gram-positive and gram-negative pathogens.
What Are Tetracyclines?
Tetracyclines are a class of broad-spectrum antibiotics that have been used in clinical medicine since the 1940s. They are effective against a wide variety of bacteria and are prescribed for numerous infectious diseases. Well-known members of this antibiotic class include doxycycline, minocycline, and tetracycline.
Mechanism of Action
Tetracyclines work by inhibiting bacterial protein synthesis. They bind reversibly to the 30S subunit of the bacterial ribosome, thereby preventing the attachment of aminoacyl-tRNA to the ribosome-mRNA complex. This disrupts the production of essential proteins within the bacterial cell, stopping bacterial replication. This mode of action is described as bacteriostatic (growth-inhibiting rather than directly killing bacteria).
Indications
Tetracyclines are used to treat a broad range of infections, including:
- Respiratory tract infections (e.g., caused by Mycoplasma pneumoniae or Chlamydophila pneumoniae)
- Skin conditions such as inflammatory acne vulgaris
- Sexually transmitted infections such as chlamydia
- Lyme disease (doxycycline is the first-line treatment)
- Rickettsial diseases and other tick- or insect-borne illnesses
- Malaria prophylaxis (doxycycline is used for travel prevention)
- Helicobacter pylori infection as part of combination therapy
Dosage and Administration
The dosage of tetracyclines depends on the specific agent, the indication, and the individual patient. Doxycycline is the most commonly used agent and is typically taken orally once daily. Key administration points include:
- Tetracyclines should not be taken with milk, dairy products, antacids, or iron-containing supplements, as these reduce absorption.
- They should be taken with plenty of water while sitting or standing upright to prevent esophageal irritation.
- Unlike older tetracyclines, doxycycline can be taken with a small meal to reduce stomach upset.
Side Effects
Like all antibiotics, tetracyclines can cause unwanted effects:
- Gastrointestinal complaints: nausea, vomiting, diarrhea
- Photosensitivity: increased sensitivity of the skin to sunlight (especially with doxycycline)
- Tooth discoloration and impaired bone development: in children under 8 years of age and during pregnancy, tetracyclines can be incorporated into developing teeth and bones
- Disruption of gut flora: possible overgrowth by fungi (e.g., Candida) or resistant bacteria
- Hepatotoxicity: rare liver damage, particularly at high doses
Contraindications
Tetracyclines are contraindicated or should be used with caution in the following situations:
- Pregnancy (especially from the second trimester onward): risk of tooth discoloration and skeletal development disorders in the child
- Children under 8 years of age: incorporation into developing teeth and bones
- Severe renal impairment: for most tetracyclines (doxycycline is an exception)
- Known hypersensitivity to tetracyclines
Antibiotic Resistance
Decades of widespread use have led many bacterial strains to develop resistance to tetracyclines. The most common resistance mechanisms involve active efflux pumps that expel the antibiotic from the bacterial cell, or ribosomal protection proteins. Newer tetracycline derivatives such as tigecycline have been developed specifically to overcome these resistance mechanisms.
References
- Chopra, I. & Roberts, M. - Tetracycline antibiotics: mode of action, applications, molecular biology, and epidemiology of bacterial resistance. Microbiology and Molecular Biology Reviews, 2001; 65(2): 232-260.
- World Health Organization (WHO) - WHO Model List of Essential Medicines, 23rd Edition, 2023. Available at: https://www.who.int/publications/i/item/WHO-MHP-HPS-EML-2023.02
- Goodman & Gilman's The Pharmacological Basis of Therapeutics. 13th Edition. McGraw-Hill Education, 2017.
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