(for veterinary information only)
250 mg OR 500 mg
Tetracycline was invented by Lloyd Conover working for Pfizer and was patented in 1955. Within three years it became the best selling antibiotic in the U.S. Tetracycline has fallen out of favor because it usually must be administered three times daily, a relatively inconvenient schedule, but it is still widely used 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 in the treatment of 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.
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. While tetracycline is not able to achieve adequate concentrations for penetration of the central nervous system and thus cannot treat infections in that location, it is able to permeate blood cells to address intracellular parasites as well as the prostate gland to treat infections there. Infectious agents for which members of the tetracycline family are especially helpful are, as mentioned, the intracellular ones including:
Another use seems to be against what are called Tetracycline Responsive Abscesses. It is not entirely clear what sort of organisms are represented here but something called an “L-form” (a bacterial type that lacks a cell wall) is sometimes involved. Often these are responsive to the tetracycline class of drugs.
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 as 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. (They bind 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 in a patient with pre-existing kidney disease.
Long term use may induce actual urinary stones made of tetracycline (a rare but interesting complication).
Tetracycline can cause a false positive urine test for glucose.
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. Iron containing vitamin supplements produce the same problem. (Iron supplements are often used concurrently with tetracycline to treat "Feline Infectious Anemia.” Administration of these two medications should be separated by a couple of hours.)
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.
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. This may not be the best choice 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 light-tight containers.
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.
Page last updated: 3/2/2012