Doxycycline is an antibiotic medicine belonging to the class called "tetracyclines." It is used to treat bacterial infections in many different parts of the body. It does not treat viral infections, such as the common cold.

Doxycycline is approved to treat anthrax in all its forms [inhaled (lung), skin, stomach and intestinal].

3. Can medicines in the same class as doxycycline be used to prevent or treat anthrax?

Other drugs in the tetracycline class carry a broad indication for illnesses caused by the anthrax organism (Bacillus anthracis). Because the most up-to-date information about appropriate dosing following exposure to anthrax is available for Cipro (ciprofloxacin), doxycycline, and penicillin G procaine, use of these three drugs has been recommended.

Antibiotic therapy should only be started in the case of suspected or confirmed exposure to anthrax. Antibiotics reduce the risk of severe disease following exposure, but do not prevent exposure.

4. What are some possible side effects of doxycycline?

Some possible uncommon but serious side effects of doxycycline include:

• a life-threatening allergic reaction (symptoms are trouble breathing; closing of the throat; swelling of the lips, tongue, or face; hives)

• blood problems (symptoms are unusual bleeding or bruising)

• liver damage (symptoms are yellowing of the skin or eyes, dark urine, nausea ,vomiting, loss of appetite, abdominal pain)

• irritation of the esophagus

Other more common, but less serious, side effects include:

• nausea, vomiting, diarrhea

• increased sensitivity of the skin to sunlight

• vaginal yeast infection

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. If a person is exposed to anthrax, the risk of side effects caused by doxycycline treatment may be acceptable because of the seriousness of the disease. However, if a person has not been exposed to anthrax, these risks may outweigh the benefits.

Some other things to consider:

• Doxycycline and other members of the tetracycline class of antibiotics are not generally approved for treating patients under 8 years old. These antibiotics can cause swelling of the brain and a condition called bulging fontanels (soft spot on head) in infants.

• Tetracycline antibiotics are associated with permanent tooth discoloration in children. If used for long periods, they may also slow down the growth of teeth and bones in babies born prematurely. However due to the seriousness of anthrax, dosing instructions for treating inhaled anthrax (post-exposure) is provided in approved prescribing information for doxycycline.

• Before taking any tetracycline antibiotic, review with your health care provider ALL medicines you are taking, including those you take without a prescription. Tetracycline antibiotics can affect how other medicines work and other medicines can affect how the antibiotic works.
• Some medicines that can interact with doxycycline are antacids and supplements that contain calcium, iron, magnesium, or sodium bicarbonate. If you take products containing these minerals within 2 hours of the time you take doxycycline, these medicines could decrease the doxycycline’s effectiveness.
• Birth control pills also may not work as well if you are taking doxycycline. Use other forms of birth control while you are taking this medicine.

• Throw away any unused doxycycline when it is out of date or when it is no longer needed. Do not take any doxycycline after the expiration date printed on the bottle.

There are online pharmacies from which you can confidently fill your prescriptions. Unfortunately, there are also questionable sites that make buying medicines online risky. Buying a medicine from an illegal Website puts you at risk. You may get a contaminated or fake product, the wrong product, an incorrect dose, or no product at all. Go to: http://www.fda.gov/oc/buyonline/default.htm for additional tips on buying medicines online.

FDA can not assure the quality or identity of products not approved for sale in the United States. Not all countries have the same approval procedures and manufacturing controls as the United States.

Possible risks include fake, unapproved, outdated, or sub-standard products. A document, entitled "Purchasing Medications Outside the United States", explains FDA’s concerns on this subject. This document can be found at: http://www.fda.gov/ora/import/purchasing_medications.htm.