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, 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 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).
The recommended dosage depends on the type of tetracycline, its strength, and the type and severity of infection for which it is being taken. Check with the physician who prescribed the drug or the pharmacist who filled the prescription for the correct dosage.
To make sure the infection clears up completely, take the medicine for as long as it has been prescribed. Do 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, take the medicine in doses spaced evenly through the day and night. Do not miss any doses.
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. Do not drink or eat milk or dairy products within 1-2 hours of taking tetracyclines (except doxycycline and minocycline).
Taking outdated tetracyclines can cause serious side effects. Do not take this medicine 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 Flush any such medicine away down the toilet. If there is any question about whether the medicine is still good, check with a physician or pharmacist.
Do not take antacids, calcium supplements, salicylates such as Magan or Trilisate, magnesium-containing laxatives, or sodium bicarbonate (baking soda) within 1-2 hours of taking tetracyclines.
Do not take any medicines that contain iron (including multivitamin and mineral supplements) within 2-3 hours of taking tetracyclines.
Some people feel dizzy when taking these drugs. The medicine may also 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 when taken while tetracyclines are being taken. To prevent pregnancy, use additional methods of birth control while taking tetracyclines.
This medicine may increase sensitivity to sunlight. Even brief exposure to sun can cause a severe sunburn or a rash. While being treated with this medicine, avoid being in direct sunlight, especially between 10 a.m. and 3 p.m.; wear a hat and tightly woven clothing that covers the arms and legs; use a sunscreen with a skin protection factor (SPF) of at least 15; protect the lips with a sun block lipstick; and do not use tanning beds, tanning booths, or sunlamps. The sensitivity to sunlight and sunlamps may continue for 2 weeks to several months after stopping the medicine, so continue to be careful about sun exposure.
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. Do not give tetracyclines to infants or children under 8 years of age unless directed to do so by the child's physician.
People with certain medical conditions or who are taking certain other medicines may have problems if they take tetracyclines. Before taking these drugs, be sure to let the physician know about any of these conditions:
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 should also be told about any allergies to foods, dyes, preservatives, or other substances.
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 can also cause liver problems in pregnant women.
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 its 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:
Use of certain medicines
- Liver disease
- Kidney disease.
Taking tetracyclines with certain other drugs may affect the way the drugs work or may increase the chance of 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.
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 the physician know all other medicines he or she is taking. Among the drugs that may interact with tetracyclines are:
- 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
- Birth control pills.
- A sexually transmitted disease (STD) that causes infection in the genital organs and may cause disease in other parts of the body.
- 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.
- A group of drugs that includes aspirin and related compounds. Salicylates are used to relieve pain, reduce inflammation, and lower fever.
Gale Encyclopedia of Medicine. Gale Research, 1999.