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Tetracyclines are medicines that kill certain infection-causing microorganisms.


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.
Interestingly, a form of tetracycline has recently been used in prevention of cancer recurrence. Chemically modified tetracyclines such as COL-3 are derived from antibiotic tetracyclines, but because of their modifications, don't act as antibiotics. Instead, they inhibit certain enzymes and processes that normally encourage cancer growth. By making cancer cells less aggressive, these drugs may show potential for long-term management of some cancers.


Tetracyclines are available only with a physician's prescription. They are sold in capsule, tablet, liquid, and injectable forms. Some commonly used medicines in this group are tetracycline (Achromycin V, Sumycin) and doxycycline (Doryx, Vibramycin).

Recommended dosage

The recommended dosage depends on the type of tetracycline, its strength, and the type and severity of infection for which it is being taken. The physician who prescribed the drug or the pharmacist who filled the prescription know the correct dosage.
To make sure the infection clears up completely, patients are told to take the medicine for as long as it has been prescribed. They should not stop taking the drug just because symptoms begin to improve.
Tetracyclines work best when they are at constant levels in the blood. To help keep levels constant, the doses are spaced evenly through the day and night. No doses should be missed.
This medicine works best when taken on an empty stomach, with a full glass of water. The water will help prevent irritation of the stomach and esophagus (the tube-like structure that runs from the throat to the stomach). If the medicine still causes stomach upset, it may be necessary to take it with food. However, tetracyclines should never be taken with milk or milk products, as these may prevent the medicine from working properly. Milk or dairy products should be avoided within one to two hours of taking tetracyclines (except doxycycline and minocycline).


Taking outdated tetracyclines can cause serious side effects. The medicine should not be taken if:
  • its color, appearance, or taste have changed
  • it has been stored in a warm or damp area
  • the expiration date on its label has passed. Any such medicine should be flushed down the toilet; if there is any question about whether the medicine is still good, the patient should check with a physician or pharmacist
Antacids, calcium supplements, such as the salicylates Magan or Trilisate, magnesium-containing laxatives, or sodium bicarbonate (baking soda) should not be taken within one to two hours of taking tetracyclines.
Medicines that contain iron (including multivitamin and mineral supplements) should not be taken within 2-3 hours of taking tetracyclines.
Some people feel dizzy when taking these drugs. The medicine also may cause blurred vision. Because of these possible effects, anyone who takes these drugs should not drive, use machines or do anything else that might be dangerous until they have found out how the drugs affect them.
Birth control pills may not work properly while tetracyclines are being taken. To prevent pregnancy, alternative methods of birth control should be used while taking tetracyclines.
This medicine may increase sensitivity to sunlight. Even brief exposure to sun can cause a severe sunburn or rash. While being treated with this medicine, direct sunlight should be avoided, especially between 10 A.M. and 3 P.M. A hat and tightly woven clothing that covers the arms and legs; a sunscreen with a skin protection factor (SPF) of at least 15; protecting the lips with a sun block lipstick; and avoiding use of tanning beds, tanning booths, or sunlamps are advised when on tetracyclines. The sensitivity to sunlight and sunlamps may continue for two weeks to several months after stopping the medicine.
Tetracyclines may permanently discolor the teeth of people who took the medicine in childhood. The drugs may also slow down the growth of children's bones. Tetracyclines are generally not given to infants or children under 8 years of age unless directed by the child's physician. The medical community continues to express concern about resistance to tetracyclines and other antibiotics. As patients continue to use, and often overuse, these medications, eventually, strains of bacteria develop resistance to the medicines. The use of tetracycline is much broader than it was 20 or 30 years ago and physicians will prescribe the medicine only when appropriate.

Special conditions

People with certain medical conditions or who are taking certain other medicines may have problems if they take tetracyclines. Before a patient takes these drugs, the physician should be advised of any of these conditions:
ALLERGIES. Anyone who has had unusual reactions to tetracyclines in the past should let his or her physician know before taking the drugs again. The physician also should be told about any allergies to foods, dyes, preservatives, or other substances.
PREGNANCY. Pregnant women should not take tetracyclines during the last half of pregnancy. These drugs can prevent the baby's bones and teeth from developing properly and can cause the baby's adult teeth to be permanently discolored. The medicine also can cause liver problems in pregnant women.
BREASTFEEDING. Women who are breastfeeding should not take tetracyclines. The drugs pass into breast milk and can affect the nursing baby's teeth and bones. They may also make the baby more sensitive to sunlight and may increase risk of fungal infections.
OTHER MEDICAL CONDITIONS. Before using tetracyclines, people with any of these medical problems should make sure their physicians are aware of their conditions:
  • diabetes
  • liver disease
  • kidney disease
USE OF CERTAIN MEDICINES. Taking tetracyclines with certain other drugs may affect the way the drugs work or may increase the chance of side effects.

Side effects

The most common side effects are stomach cramps or a burning sensation in the stomach, mild diarrhea, nausea, or vomiting. These problems usually go away as the body adjusts to the drug and do not require medical treatment. Less common side effects, such as sore mouth or tongue and itching of the rectal or genital areas also may occur and do not need medical attention unless they do not go away or they are bothersome.
Other rare side effects may occur. Anyone who has unusual symptoms during or after treatment with tetracyclines should get in touch with his or her physician.

Key terms

Gonorrhea — A sexually transmitted disease (STD) that causes infection in the genital organs and may cause disease in other parts of the body.
Microorganism — An organism that is too small to be seen with the naked eye.
Rocky Mountain spotted fever — An infectious disease that is caused by a microorganism and spread by ticks. High fever, muscle pain, and spots on the skin are among the symptoms.
Salicylates — A group of drugs that includes aspirin and related compounds. Salicylates are used to relieve pain, reduce inflammation, and lower fever.


Tetracyclines may interact with other medicines. When this happens, the effects of one or both of the drugs may change or the risk of side effects may be greater. Anyone who takes tetracyclines should let a physician know all other medicines he or she is taking. Among the drugs that may interact with tetracyclines are:
  • antacids
  • calcium supplements
  • medicines that contain iron (including multivitamin and mineral supplements)
  • laxatives that contain magnesium
  • cholesterol-lowering drugs such as cholestyramine (Questran) and colestipol (Colestid)
  • salicylates such as Magan and Trilisate
  • penicillins
  • birth control pills



"Modified Tetracycline May Help Prevent Cancer Recurrence." Cancer Weekly December 10, 2002: 2.
Roberts, Marilyn C. "Tetracycline Therapy: Update." Clinical Infectious Diseases February 15, 2003: 462-466.
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
The best option to prevent intrinsic staining in children is to avoid too much fluoride and tetracycline antibiotics for the mother.
The 470-nm visible blue wavelengths used to initiate polymerization of light-cured restorative materials affect tetracycline antibiotics differently, with demeclocycline being more reactive to light than doxycycline (27).
There were no positive results found for the [beta]-lactams, but all five samples had positive results for both aminoglycoside and tetracycline antibiotics. The highest levels were found for both gentamicin and neomycin of the aminoglycoside class of antibiotics and chlortetracycline of the tetracycline class of antibiotics, with over 100 times the amount compared with the parameters set by Eurofins Analytical Laboratory, Inc.
[209] stated in a recent review that mitochondria are affected by tetracycline antibiotics. The authors demonstrated that doxycycline disturbs mitochondrial proteostasis and metabolic activity and induces widespread gene expression changes [209].
Escherichia coli isolates recovered from uteri of infertile mares were 100% sensitive to Cefuroxime, Ceftriaxone, Chloramphenicol, Gentamicin and Tetracycline antibiotics and 50% isolates were susceptible to Ciprofloxacin.
Pectin can have a moderate interaction with the following drugs: tetracycline antibiotics; Digoxin (Lanoxin) a cardiovascular medicine; and Lovastatin (Mevacor), a statin that lowers cholesterol.
Despite the fact that the ability of EGCG to effectively increase the anti-staphylococcal effect of tetracycline has previously been described, its interaction with other tetracycline antibiotics has poorly been studied.
Tetracycline antibiotics: made of action, applications, molecular biology and epidemiology of bacterial resistance.
Fewer than 10% of Staphylococcus aureus isolates showed resistance to long-term use of tetracycline antibiotics in a cross-sectional study of 83 patients with acne.
Cale et al suggested that Minocycline, a synthetic compound of tetracycline antibiotics is also implicated in causing discoloration in an adult patient, following its long term use for treatment of acne.
Tetracycline antibiotics are ranked second in production and usage worldwide, and first in China (Gu and Karthikeyan 2005).
You need tetracycline antibiotics. Ask your doctor.