What are 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
aminoacyltransfer-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 the drug will 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 of liver toxicity.

All agents in this class can lead to photosensitivity, so persons should be advised to limit sun exposure to avoid serious sunburn, particularly when first beginning the medication. This reaction is most common with demeclocycline.

Another unique issue related to tetracyclines is the presence of a Fanconi-like 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 prophylaxis. Minocycline and doxycycline are most commonly used. 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 also are commonly included in animal feed.

Bibliography

“Antibiotics and Antimicrobial Agents.” Foye’s Principles of Medicinal Chemistry. Ed. by Thomas L. Lemke, et al. 7th ed. Philadelphia: Lippincott, 2013. Print.

Murray, Patrick R., Ken S. Rosenthal, and Michael A. Pfaller. Medical Microbiology. 8th ed. Philadelphia: Mosby/Elsevier, 2016. Print.

Sanford, Jay P., et al. The Sanford Guide to Antimicrobial Therapy. 45th ed. Sperryville: Antimicrobial Therapy, 2015. Print.

Tortora, Gerard J., Berdell R. Funke, and Christine L. Case. “Antimicrobial Drugs.” Microbiology: An Introduction. 10th ed. San Francisco: Benjamin Cummings, 2010. Print.