Tetracyclines are used to treat infections and to help control acne. Demeclocycline, doxycycline, and minocycline also may be used for other problems as determined by your doctor. Tetracyclines will not work for colds, flu, or other virus infections.

The dose of these medicines will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of these medicines. If your dose is different, do not change it unless your doctor tells you to do so.

The number of capsules, tablets, or teaspoonfuls of suspension that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are taking a tetracycline.

* For demeclocycline For oral dosage form (tablets):
o For bacterial or protozoal infections:
+ Adults and teenagers—150 milligrams (mg) every six hours; or 300 mg every twelve hours. Gonorrhea is treated with 600 mg on the first day, then 300 mg every twelve hours for four days.
+ Children older than 8 years of age—Dose is based on body weight. The usual dose is 1.65 to 3.3 mg per kilogram (kg) (0.8 to 1.5 mg per pound) of body weight every six hours; or 3.3 to 6.6 mg per kg (1.5 to 3 mg per pound) of body weight every twelve hours.
+ Infants and children 8 years of age and younger—Tetracyclines usually are not used in young children because tetracyclines can permanently stain teeth.

* For doxycycline For oral dosage forms (capsules, suspension, and tablets):
o For bacterial or protozoal infections:
+ Adults and children older than 8 years of age who weigh more than 45 kilograms (kg) (99 pounds)—100 milligrams (mg) every twelve hours the first day, then 100 mg once a day or 50 to 100 mg every twelve hours.
+ Children older than 8 years of age who weigh 45 kg (99 pounds) or less—Dose is based on body weight. The usual dose is 2.2 mg per kg (1 mg per pound) of body weight two times a day on the first day, then 2.2 to 4.4 mg per kg (1 to 2 mg per pound) of body weight once a day or 1.1 to 2.2 mg per kg (0.5 to 1 mg per pound) of body weight twice a day.
+ Infants and children 8 years of age and younger—Tetracyclines are usually not used in young children because tetracyclines can permanently stain teeth.
o For the prevention of malaria:
+ Adults and teenagers—100 mg once a day. You should take the first dose one or two days before travel to an area where malaria may occur, and continue taking the medicine every day throughout travel and for four weeks after you leave the malarious area.
+ Children older than 8 years of age—Dose is based on body weight. The usual dose is 2 mg per kg (0.9 mg per pound) of body weight once a day. You should take the first dose one or two days before travel to an area where malaria may occur, and continue taking the medicine every day throughout travel and for four weeks after you leave the malarious area.
+ Infants and children 8 years of age and younger—Tetracyclines are usually not used in young children because tetracyclines can permanently stain teeth.
* For injection dosage form:
o For bacterial or protozoal infections:
+ Adults and children older than 8 years of age who weigh more than 45 kg of body weight (99 pounds)—200 mg injected slowly into a vein once a day; or 100 mg injected slowly into a vein every twelve hours the first day, then 100 to 200 mg injected slowly into a vein once a day or 50 to 100 mg injected slowly into a vein every twelve hours.
+ Children older than 8 years of age who weigh 45 kg of body weight (99 pounds) or less—Dose is based on body weight. The usual dose is 4.4 mg per kg (2 mg per pound) of body weight injected slowly into a vein once a day; or 2.2 mg per kg (1 mg per pound) of body weight injected slowly into a vein every twelve hours the first day, then 2.2 to 4.4 mg per kg (1 to 2 mg per pound) of body weight once a day, or 1.1 to 2.2 per kg (0.5 to 1 mg per pound) of body weight every twelve hours.
+ Infants and children 8 years of age and younger—Tetracyclines are usually not used in young children because tetracyclines can permanently stain teeth.

Along with its needed effects, a medicine may cause some unwanted effects. In some infants and children, tetracyclines may cause the teeth to become discolored. Even though this may not happen right away, check with your doctor as soon as possible if you notice this effect or if you have any questions about it.

* For all tetracyclines
o More common
+ Increased sensitivity of skin to sunlight (rare with minocycline)

o Rare
+ Abdominal pain; bulging fontanel (soft spot on head) of infants; headache; loss of appetite; nausea and vomiting ; visual changes; yellowing skin

* For demeclocycline only
o Less common
+ Greatly increased frequency of urination or amount of urine; increased thirst; unusual tiredness or weakness

* For minocycline only
o Less common
+ Pigmentation (darker color or discoloration) of skin and mucous membranes

Other side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. However, check with your doctor if any of the following side effects continue or are bothersome:

* For all tetracyclines
o More common
+ Cramps or burning of the stomach; diarrhea

o Less common
+ Itching of the rectal or genital (sex organ) areas; sore mouth or tongue

* For minocycline only
o More common
+ Dizziness, light-headedness, or unsteadiness

In some patients tetracyclines may cause the tongue to become darkened or discolored. This effect is only temporary and will go away when you stop taking this medicine.

Other side effects not listed above may also occur in some patients. If you notice any other effects, check with your doctor.

If overdose is suspected, contact your local poison control center or emergency room immediately.

DO NOT SHARE THIS MEDICINE with others for whom it was not prescribed. DO NOT USE THIS MEDICINE for other health conditions. KEEP THIS MEDICINE out of the reach of children.

If you miss a dose of this medicine, apply it as soon as possible. However, if it is almost time for your next application, skip the missed dose and go back to your regular dosing schedule.

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For tetracyclines, the following should be considered:

Allergies—Tell your doctor if you have ever had any unusual or allergic reaction to any of the tetracyclines or combination medicines containing a tetracycline. Also tell your health care professional if you are allergic to any other substances, such as foods, preservatives, or dyes. In addition, if you are going to be given oxytetracycline by injection, tell your doctor if you have ever had an unusual or allergic reaction to ``caine-type'' anesthetics (e.g., lidocaine).

Pregnancy—Use is not recommended during the last half of pregnancy. If tetracyclines are taken during that time, they may cause the unborn infant's teeth to become discolored and may slow down the growth of the infant's teeth and bones. In addition, liver problems may occur in pregnant women, especially those receiving high doses by injection into a vein.

Breast-feeding—Use is not recommended since tetracyclines pass into breast milk. They may cause the nursing baby's teeth to become discolored and may slow down the growth of the baby's teeth and bones. They may also increase the sensitivity of nursing babies' skin to sunlight and cause fungus infections of the mouth and vagina. In addition, minocycline may cause dizziness, light-headedness, or unsteadiness in nursing babies.

Children—Tetracyclines may cause permanent discoloration of teeth and slow down the growth of bones. These medicines should not be given to children 8 years of age and younger unless directed by the child's doctor.

Older adults—Many medicines have not been studied specifically in older people. Therefore, it may not be known whether they work exactly the same way they do in younger adults or if they cause different side effects or problems in older people. There is no specific information comparing use of tetracyclines in the elderly with use in other age groups.

Other medicines—Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking tetracyclines, it is especially important that your health care professional know if you are taking any of the following:

* Antacids or
* Calcium supplements such as calcium carbonate or
* Cholestyramine (e.g., Questran) or
* Choline and magnesium salicylates (e.g., Trilisate) or
* Colestipol (e.g., Colestid) or
* Iron-containing medicine or
* Laxatives (magnesium-containing) or
* Magnesium salicylate (e.g., Magan)—Use of these medicines with tetracyclines may decrease the effect of tetracyclines

* Oral contraceptives (birth control pills) containing estrogen—Use of birth control pills with tetracyclines may decrease the effect of the birth control pills and increase the chance of unwanted pregnancy
* Penicillins—Use of tetracyclines with penicillins may decrease the effect of penicillins

Other medical problems—The presence of other medical problems may affect the use of tetracyclines. Make sure you tell your doctor if you have any other medical problems, especially:

* Diabetes insipidus (water diabetes)—Demeclocycline may make the condition worse

* Kidney disease (does not apply to doxycycline or minocycline)—Patients with kidney disease may have an increased chance of side effects

* Liver disease—Patients with liver disease may have an increased chance of side effects if they use doxycycline or minocycline

Keep out of the reach of children.
Store away from heat and direct light.
Keep the medicine from freezing.
Do not keep outdated medicine or medicine no longer needed. Be sure that any discarded medicine is out of the reach of children.

If your symptoms do not improve within a few days (or a few weeks or months for acne patients), or if they become worse, check with your doctor.
Oral contraceptives (birth control pills) containing estrogen may not work properly if you take them while you are taking tetracyclines. Unplanned pregnancies may occur. You should use a different or additional means of birth control while you are taking tetracyclines. If you have any questions about this, check with your health care professional.
Before having surgery (including dental surgery) with a general anesthetic, tell the medical doctor or dentist in charge that you are taking a tetracycline. This does not apply to doxycycline, however.
Tetracyclines may cause your skin to be more sensitive to sunlight than it is normally. Exposure to sunlight, even for brief periods of time, may cause a skin rash, itching, redness or other discoloration of the skin, or a severe sunburn. When you begin taking this medicine:
* Stay out of direct sunlight, especially between the hours of 10:00 a.m. and 3:00 p.m., if possible.
* Wear protective clothing, including a hat. Also, wear sunglasses.
* Apply a sun block product that has a skin protection factor (SPF) of at least 15. Some patients may require a product with a higher SPF number, especially if they have a fair complexion. If you have any questions about this, check with your health care professional.
* Apply a sun block lipstick that has an SPF of at least 15 to protect your lips.
* Do not use a sunlamp or tanning bed or booth.
You may still be more sensitive to sunlight or sunlamps for 2 weeks to several months or more after stopping this medicine. If you have a severe reaction, check with your doctor.
For patients taking minocycline:
* Minocycline may also cause some people to become dizzy, lightheaded, or unsteady. Make sure you know how you react to this medicine before you drive, use machines, or do anything else that could be dangerous if you are dizzy or are not alert. If these reactions are especially bothersome, check with your doctor.