THE PET PHARMACY By Wendy C. Brooks, DVM, DipABVP Educational Director, VeterinaryPartner.com

(for veterinary information only)

Brand Name: Vibramycin

Available as oral syrup or suspension

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). 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.

Doxycycline 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:

• Haemobartonella felis (agent of feline infectious anemia) 
• Borrelia burgdorferi (agent of Lyme disease) 
• Chlamydia psittaci (an agent of feline upper respiratory infection) 
• Ehrlichia species (a tick-borne organism) 
• Mycoplasma species (in upper respiratory and urinary infections)

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.

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.)

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 does not require refrigeration.

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.

Doxycycline is made for human children and is thus raspberry flavored. Some animals (particularly cats) do not like this taste.

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

Date Published: 1/1/2001
Date Reviewed/Revised: 07/06/2008