Doxycycline

(for veterinary information only)

BRAND NAME: VIBRAMYCIN

Available as         
ORAL SYRUP or     
SUSPENSION and    
20 mg, 50 mg and 100 mg
TABLETS, and       
20 mg, 50 mg and 100 mg
CAPSULES          

HOW THIS MEDICINE WORKS

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.

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 or organs with special barriers). Infections behind these barriers can be difficult to treat. Doxycycline represents a modification of the basic tetracycline structure to enhance its ability to penetrate such biological barriers and to increase its duration of action. Though unable to reach adequate concentrations in the central nervous system, doxycycline is able to penetrate the prostate gland to treat infections there and can permeate cells to address intracellular parasites. Infectious agents for which members of the tetracycline family are especially helpful are, as mentioned, the intracellular ones including:

  • Mycoplasma hemofelis (agent of Feline Infectious Anemia)
     
  • Borrelia burgdorferi (agent of Lyme disease)
     
  • Chlamydophila felis (an agent of feline upper respiratory infection)
     
  • Ehrlichia species (a tick-borne organism)
     
  • Mycoplasma species (in upper respiratory and urinary infections)
     
  • Doxycyline has been used in the treatment of heartworm infection, not to kill the worms but to kill the Wolbachia bacteria carried by the heartworms. Wolbachia may increase the tendency for embolism to complicate heartworm disease treatment so killing the Wolbachia prior to killing the adult heartworms is often included in the heartworm treatment protocol.

Doxycycline has also proven useful in combating "methicillin-resistant Staph aureus" (human) and "methicillin-resistant Staph intermedius" (pet) infections. These infections involve Staphylococci (bacteria) which are resistant to the drugs that Staphylococci have previously been predictably sensitive to.

Of course, there are plenty of less exotic bacteria against which doxycycline may be used. These include: Bordetella bronchiseptica (the chief agent of Kennel Cough) and bacteria of the genus Brucella.

Doxycycline also has properties by which it modifies immune-mediated diseases. This "immuno-modulating" effect is separate from its antibacterial effects and is useful in treating such conditions as: discoid lupus erythematosus, plasma cell pododermatitis, and other immune-mediated skin diseases. Often doxycycline is combined with the B vitamin, niacinamide, to enhance results in such situations.

SIDE EFFECTS

Nausea and vomiting are the most commonly reported side effects of doxycycline in dogs and cats. If this side effect occurs, it is most easily managed by giving the medication with food. (Other members of the tetracycline class should not be given with food as food binds the drug and prevents its absorption into the body. With doxycycline this is effect is not considered significant.)

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.) Doxycycline has the least potential for doing this of all of the tetracycline-type antibiotics.

The tablets have a particularly irritating pH should they become stuck in the esophagus of a smaller patient (especially a cat). If the pill sits in the esophagus, it can cause enough irritation to eventually lead to a scar causing difficulty swallowing. This can be prevented by following the pill with at least 6cc of water or, better yet, using one of the liquid formulations.

Certain types of urine dipstick tests can erroneously test positive for glucose in patients on tetracycline-type medications.

INTERACTIONS WITH OTHER DRUGS

Antacids commonly contain calcium, which binds doxycycline 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 doxycycline to treat feline infectious anemia. Administration of these two medications should be separated by a couple of hours or an injectable iron supplement may be employed.)

Nausea may result if doxycycline 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.

CONCERNS AND CAUTIONS

Doxycycline oral suspension does not require refrigeration. Tablets and capsules should be stored away from light.

The reconstituted oral suspension is only good for 2 weeks. After that, it must be discarded.

Doxycycline 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.

Page last updated: 5/27/2013