Tetracycline antibiotics
Tetracycline antibiotics are a group of broad-spectrum antibiotics derived from the Streptomyces bacteria, effective against various gram-positive and gram-negative bacteria. While not typically first-line treatments, they are frequently prescribed for conditions like acne, Lyme disease, anthrax infections, and certain sexually transmitted diseases, including chlamydia. These antibiotics function as bacteriostatic agents by inhibiting protein synthesis at the ribosomal level, which prevents bacterial growth. Common medications in this class include tetracycline, doxycycline, demeclocycline, and minocycline, all of which are orally administered.
However, tetracyclines can cause side effects like nausea and photosensitivity, and they are contraindicated for children under twelve and pregnant women due to potential risks like dental discoloration and liver toxicity. The use of tetracycline antibiotics in both human medicine and animal feed has raised concerns about antibiotic resistance. Despite these challenges, newer tetracycline-class antibiotics continue to be developed to address these public health issues.
Subject Terms
Tetracycline antibiotics
Definition
Tetracycline, which is produced by Streptomyces spp., is a broad-spectrum antibiotic that is useful against a wide range of gram-positive and gram-negative bacteria. Tetracyclines are not generally first-line agents but are still often prescribed. Activity is similar to the macrolide antibiotics, such as erythromycin. Tetracyclines are commonly used as topical or oral agents for acne. They are also among the drugs of choice for Lyme disease and anthrax infection and remain somewhat commonly used against rickettsial infections and sexually transmitted diseases, especially chlamydia.
Mechanism of Action
Tetracyclines are bacteriostatic agents that work by inhibiting protein synthesis at the ribosomal level. They bind to ribonucleic acid (RNA) at the 30S site and then inhibit subsequent binding of the aminoacyl-transfer-RNA to the ribosome. This action terminates peptide chain growth. More lipophilic agents in this class, such as minocycline, also disrupt cytoplasmic membrane function and cause key cellular components to leak from the cell, leading to cell death.
Drugs in This Class
The common drugs in this class are tetracycline, doxycycline, demeclocycline, and minocycline. They are well absorbed and can be taken by mouth. They should not, however, be taken within two hours of ingesting dairy products, antacids, or other foods or multivitamin and mineral preparations that contain calcium, iron, aluminum, or magnesium; chelation of the drug with the metal ion will result. The drug will then become insoluble and not be properly absorbed.
Drugs in this class are associated with nausea, vomiting, diarrhea, dizziness, and vertigo. Like other broad-spectrum antibiotics, they frequently lead to superinfection, particularly of Candida albicans. They should not be prescribed to children under the age of twelve years because they are highly associated with a progressive and permanent discoloration of teeth, particularly during the years in which the permanent set is developing. They also are not advised for pregnant women because of the potential for liver toxicity.
All agents in this class can lead to photosensitivity, so people should be advised to limit sun exposure to avoid serious sunburn, particularly when beginning the medication. This reaction is most common with demeclocycline.
Another unique issue related to tetracyclines is the presence of a Fanconi syndrome caused by anhydro-4-epitetracycline, a degradation product that can form over time; it is toxic to the kidneys and can be fatal. For this reason, outdated or expired tetracycline and demeclocycline should never be taken. Because the degradation product is formed by a dehydration reaction at C-6, only tetracyclines that have a C-6 hydroxyl group are at risk for this problem. Minocycline and doxycycline do not have this group and are free of this toxicity.
Impact
Tetracycline products are most often used for acne and for Lyme disease treatment. Minocycline and doxycycline are most commonly used. Tetracyclines are also prescribed for respiratory infections; sexually transmitted infections, such as chlamydia and syphilis; and rickettsial infections, such as Rocky Mountain spotted fever. Doxycycline, which received widespread attention in the wake of the 2001 anthrax bioterrorism scare in the United States, is one of the primary agents used for anthrax, including inhalation anthrax. Tetracyclines are also commonly included in animal feed. The widespread use of tetracyclines has led to critical public health issues surrounding antibiotic resistance, although new tetracycline-class antibiotics have emerged.
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