Tetracyclines are called broad-spectrum antibiotics because they can be used to treat a wide variety of infections. Physicians may prescribe these drugs to treat eye infections, pneumonia, gonorrhea, Rocky Mountain spotted fever, urinary tract infections, certain bacteria that could be used in biological weapons, and other infections caused by bacteria. The medicine is also used to treat acne. The tetracyclines will not work for colds, flu, and other infections caused by viruses. Tetracyclines are generally a low-cost alternative among antibiotics.
There are five drugs in the tetracycline class:
All tetracyclines are used for treatment of infections in patients over the age of eight years. They may be used in several forms, including capsules, injections, ointments, eye and ear drops.
Tetracyclines are bacteriostatic. They do not kill bacteria; they prevent bacteria from growing, so that the body's natural defenses are better able to deal with an infection. For this reason, tetracyclines are not used in patients with impaired immune systems.
Although all tetracyclines are similar, and can do most of the same work, there are some differences. Doxycycline requires only one dose a day and can be used even when the patient has kidney problems. Demeclocycline and minocycline penetrate the skin better than other tetracyclines and may be preferred for treatment of acne. Demeclocycline is effective for the syndrome of inappropriate anti-diuretic hormone (SIDAH), although it is not officially approved for this purpose.
In addition to their role in treating infections, tetracyclines have a wide range of other uses. These include protection against some types of malaria and treatment of some of the infections that might be used in bioterrorism. Some tetracycline derivatives have been useful in cancer therapy. Tetracyclines have been useful in prevention of gum diseases of the mouth.
Tetracyclines should normally not be used in children under the age of eight because some tetracyclines can be absorbed into the bones and teeth and give the teeth a mottled appearance. Some experts believe that tetracyclines should be avoided in children younger than ten.
Not all tetracyclines have the same side effects, but the following list includes some of the most common problems:
- dizziness and lightheadedness
- stomach upset
- fungus infections
- tooth discoloration
- mouth irritation
- skin discoloration
On rare occasions tetracyclines may cause more severe adverse effects, including kidney damage and drug-induced lupus.
Moreover, tetracyclines may reduce the effectiveness of oral contraceptives.
Many antibiotics share tetracyclines' interaction with neuromuscular blocking agents. Tetracyclines should not be used at the same time as neuromuscular blocking agents since the antibiotics can increase the strength of the neuromuscular blocker, which can make breathing difficult. While this interaction is severe, it is rare, since the neuromuscular blocking agents are usually used only in surgery.
Tetracyclines should not be taken at the same time as foods containing calcium or foods containing iron, magnesium, or aluminum. The metals bind to the tetracycline, and the combination has reduced effect on bacteria.
Although it is recommended that tetracyclines not be given to children under the age of eight, the drug is sometimes required in severe infections. Tetracyclines may be required for children who have developed infections either in hospitals or while traveling overseas.
Parents should carefully check the expiration date of tetracycline and not use the drug past the expiration date. Expired tetracycline has been known to cause a severe kidney problem called Fanconi syndrome. Expired tetracycline should be disposed of, not saved.
Because tetracyclines can cause photosensitization, patients taking these drugs should use sunscreen and avoid direct sunlight.
Because of their interaction with metals, tetracyclines should always be taken on an empty stomach with only water. Patients should particularly avoid calcium-containing dairy products and antacids as well as multivitamin-mineral supplements.
Tetracyclines inhibit the growth of many bacteria and other microorganisms which can lead to overgrowth of other microorganisms. Possible symptoms are discoloration of the tongue and diarrhea. Parents should report these problems to the prescriber immediately.
Parents should alert all health-care professionals about all drugs their children are taking. Both tetracycline and oral contraceptives are used to treat acne in teenage girls, but these drugs should not be used together.
Antibiotics—Drugs that are designed to kill or inhibit the growth of the bacteria that cause infections.
Bacteriostatic—An agent that prevents the growth of bacteria.
Fanconi's syndrome—A group of disorders involving kidney tubule malfunction and glucose, phosphate, and bicarbonate in the urine. Two forms of this syndrome have been identified: an inherited form and an acquired form caused by vitamin D deficiency or exposure to heavy metals.
Photosensitization—Development of oversensitivity to sunlight.
See also Penicillins.
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Samuel Uretsky, PharmD