Tetracyclines
Tetracycline is a broad spectrum polyketide antibiotic produced by the Streptomyces genus of Actinobacteria. It exerts a bacteriostatic effect on bacteria by binding reversible to the bacterial 30S ribosomal subunit and blocking incoming aminoacyl tRNA from binding to the ribosome acceptor site. It also binds to some extent to the bacterial 50S ribosomal subunit and may alter the cytoplasmic membrane causing intracellular components to leak from bacterial cells.
The tetracyclines are a group of anti-infectives composed of natural and semisynthetic compounds. They are useful in select infections when the organism shows sensitivity to the tetracyclines, such as in cholera, Rocky Mountain spotted fever, and typhus.Tetracyclines are broad-spectrum against many bacteria and treat conditions such as acne, urinary tract infections (UTIs), intestinal tract infections, eye infections, sexually transmitted diseases, periodontitis (gum disease), and other bacterial infections.
MODE OF ACTION
The tetracyclines exert their effect by inhibiting bacterial protein synthesis, which is a process necessary for reproduction of the microorganism. The ultimate effect of this action is that the bacteria are either destroyed or their multiplication rate is slowed. The tetracyclines are bacteriostatic (capable of slowing or retarding the multiplication of bacteria), whereas the macrolides and lincosamides may be bacteriostatic or bactericidal (capable of destroying bacteria).
USES
These antibiotics are effective in the treatment of infections caused by a wide range of gram-negative and grampositive microorganisms. The tetracyclines are used in infections caused by Rickettsiae (Rocky Mountain spotted fever, typhus fever, and tick fevers). Tetracyclines are also used in situations in which penicillin is contraindicated, in the treatment of intestinal amebiasis, and in some skin and soft tissue infections. Oral tetracyclines are used in the treatment of uncomplicated urethral, endocervical, or rectal infections caused by Chlamydia trachmatis and as adjunctive treatment in severe acne. Tetracycline in combination with metronidazole and bismuth subsalicylate is useful in treating Helicobacter pylori (a bacteria in the stomach that can cause peptic ulcer).
CONTRAINDICATIONS
The tetracyclines are contraindicated if the patient is known to be hypersensitive to any of the tetracyclines. Tetracyclines also are contraindicated during pregnancy because of the possibility of toxic effects to the developing fetus. The tetracyclines are classified Pregnancy Category D drugs. These drugs also are contraindicated during lactation and in children younger than 9 years (may cause permanent discoloration of the teeth).
PRECAUTIONS
It is important to use the tetracyclines cautiously in patients with renal function impairment. In addition, doses greater that 2 g/d can be extremely damaging to the liver. The nurse should carefully check the expiration dates of the tetracyclines before administration because degradation of the tetracyclines can occur; after degradation, the agents are highly toxic to the kidneys.
INTERACTIONS
Antacids containing aluminum, zinc, magnesium, or bismuth salts, or foods high in calcium impair absorption of the tetracyclines. When the tetracyclines are administered with oral anticoagulants, an increase in the effects of the anticoagulant may occur. When tetracyclines are administered to women using oral contraceptives, a decrease in the effect of the oral contraceptive may be seen. This may result in breakthrough bleeding or pregnancy. When digoxin is administered with the tetracyclines there is an increased risk for digitalis toxicity. The effects of this could last for months after tetracycline administration is discontinued. Tetracyclines may reduce insulin requirements. Blood glucose levels should be monitored frequently during tetracycline therapy.
The tetracycline class contains well-known drugs such as:
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doxycycline
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tetracycline
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minocycline
