Brand Names: Panmycin, Tetracap, Tetracyn, Sumycin, Tetralan

Available as 250 mg, 500 mg capsules or an oral suspension

How this Medication Works

Tetracycline was patented in 1955. Within three years it became the best selling antibiotic in the U.S. and was widely used in both human and veterinary medicine. Tetracycline has since been supplanted, at least in small animal medicine, by minocycline and doxycycline, which have less potential for side effects and more convenient dosing schedules. Tetracycline has become expensive and difficult to obtain but is still in use as it has a unique ability to penetrate cells and attack infections there. Tetracycline also has some ability to modulate the immune system, an effect separate from its antibiotic abilities, and it is sometimes used to treat immune-mediated conditions (see below for details).

The tetracycline antibiotic family provides broad anti-bacterial protection by inhibiting bacterial protein synthesis. The mammalian host's protein synthesis mechanisms are not affected because of basic differences in the shape of the cellular machinery (the ribosomes) used to translate RNA into protein. In other words, tetracycline binds to bacterial protein-synthesis structures but not to mammalian ones.

Uses of this Medication 

The body possesses many barriers through which antibiotics have difficulty penetrating (the nervous system, prostate gland, and eye are some examples). Infections behind these barriers can be difficult to treat. Tetracycline is effective in treating prostate infections and can permeate cells to address intracellular parasites. It cannot reach adequate concentrations in the central nervous system to treat infections there, though. Infectious agents for which members of the tetracycline family are especially helpful are, as mentioned, the intracellular ones including:

• Hemobartonella felis - now renamed Mycoplasma hemofelis (agent of feline infectious anemia)
• Borrelia burgdorferi (agent of Lyme disease)
• Chlamydia psittaci (an agent of feline upper respiratory infection)
• Erlichia species (a tick-borne organism)
• Mycoplasma species (in upper respiratory and urinary infections)
• Beyond antibiotic properties, tetracyclines also appear to have anti-inflammatory properties that have given them a place in treating assorted immune-mediated skin conditions in particular: discoid lupus erythematosus.

Another use would be treating a feline condition known as a tetracycline responsive abscess in which draining abscesses are caused by L-form bacteria (a bacterial type that lacks a cell wall). Treatment of choice for this condition employs members of the tetracycline family.

Side Effects

Nausea and vomiting are the most commonly reported side effects of tetracycline in dogs and cats, particularly cats. Tetracycline should not be given with food because food binds the drug and prevents its absorption into the body.

Drugs of the tetracycline class have potential to permanently stain teeth if given to immature animals. (It binds to calcium, which is needed for growing bones and teeth.)

Tetracyclines have potential to be toxic to the kidney. It is best to pick another drug for a patient with pre-existing kidney disease.

Long-term use may induce urinary stones made of tetracycline - a rare but interesting complication.

Tetracycline can cause a false positive urine test for glucose.

Interactions with other Drugs

Antacids commonly contain calcium, which binds tetracycline in the GI tract. If these medications are used together, neither may be absorbed properly and the benefits of both are lost. Vitamin supplements containing iron produce the same problem. (Iron supplements are often used concurrently with tetracycline to treat feline infectious anemia. Administer of these two medications should be separated by a couple of hours if both are given by mouth.)

Nausea may result if tetracycline is used in combination with theophylline (an airway dilator). These two drugs might be used together to treat kennel cough.

Drugs of the tetracycline class may make digoxin (a heart medication) act stronger.

Giving sucralfate (as might be used for stomach ulcers) should be staggered with tetracycline by a couple of hours. The sucralfate will bind the tetracycline and prevent it from entering the body.

Cautions and Concerns

Tetracycline does not kill bacteria; it merely curtails their ability to reproduce. For the invading bacteria to be killed, the host's immune system must be active and effective. Tetracycline may not be the best choice of medication for immune-compromised patients.

Because of the calcium binding issues, tetracycline should not be used in pregnant patients.

Tetracyclines should be stored at room temperature in a light-tight container.

If you miss a dose, do not double up on the next dose. Simply give the medication when it is remembered or pick up with the next dose, allowing at least the proper interval between doses according to the label instructions.

Dosage adjustments are required if tetracycline is to be used in patients with liver or kidney disease.

Doxycycline, a relative of tetracycline, offers some advantages with regard to side effects and dosing schedule. Usage of doxycycline has largely supplanted tetracycline in most situations.

It is our policy not to give dosing information over the Internet.