The Side Effects of Doxycycline for Cats

Doxycycline is an antibiotic prescribed in cats to treat Lyme disease, Rocky Mountain spotted fever and Feline chlamydophila (formerly known as chlamydia). It may also be used to treat other bacterial infections that respond to its presence. Marketed under the brand names "Vibramycin" and "Doryx", it was developed in the 1960's by Pfizer, Inc. to become their first once-a-day broad-spectrum antibiotic.

What is Doxycycline?

Doxycycline is in the branch of antibiotics known as tetracyclines, a broad-spectrum branch of protein synthesis inhibitors that work to break the protein of bacteria. They are often prescribed against infections of the respiratory tract, sinuses, urinary tract and intestines. It is also effective against:

  • Leptospirosis (Weil's disease or "Fort Bragg" fever)
  • Toxoplasmosis
  • Mycoplasma bacteria
  • Psittacosis (Parrot fever)
  • Ehrlichiosis (a tick-borne disease)
  • Salmon poisoning

Due to the development of bacterial resistance, tetracycline antibiotics are no longer as effective as they once were, but are still sometimes prescribed against bacteria upon which they do have an effect.

Side Effects

Though Doxycycline is among the safer of the tetracycline antibiotics, it still comes with several side effects, some potentially life-threatening. Additionally, many animals are allergic to tetracyclines, so an allergy test should be run before administering the prescription.

Mild Side Effects

The most common side effects of Doxycycline's use in cats are vomiting and nausea. These side effects can often be avoided by giving the medication with food, or on a full stomach. However, if the symptoms persist, your cat may be having an allergic reaction.

Additionally, the drug is shown to make some animals slightly photosensitive, so care should be taken to prevent sunburns.

Diarrhea is also a fairly common side effect of Doxycycline and is generally not serious. However, should the diarrhea be watery or contain blood, you should call your veterinarian immediately.

Serious Side Effects

If your cat experiences any of the following serious side effects, you should seek medical attention immediately:

  • Severe headache
  • Dizziness
  • Fever
  • Hair loss
  • Lesions
  • Vesicles around the mouth, ears or groin
  • No urination
  • Dark urine
  • Confusion
  • Weakness
  • Loss of appetite
  • Jaundice
  • Irritation of the Esophagus

Due to the pH of Doxycycline, it is not uncommon for the tablets to become stuck in the esophagus of a cat. This can cause irritation, even scarring which may make it difficult for your cat to swallow. To prevent this, it is suggested that you follow the pill with water to thoroughly wash it down. Do not give this medication with milk or dairy products.

Though the popularity and use of tetracyclines (and with them, Doxycycline as well) has declined, it is one of the few medications effective against Rocky Mountain spotted fever, a disease to which cats are susceptible. As with all tetracyclines, it carries the risk of severe side effects, so careful dosage and administration is required.