Use of doxycycline in cats and dogs

Doxycycline (Ronaxan, Tabernil Doxycycline, Vibravenos) is a broad-spectrum antibiotic that is very effective at eliminating gram-positive and gram-negative microorganisms. It is a derivative of oxytetracycline and both belong to the tetracycline group.

Doxycycline in dogs

Its mechanism of action is akin to other tetracyclines as it works by blocking the 30S subunit, thus inhibiting mRNA and tRNA binding. This means the bacteria cannot synthesise proteins. The 30S subunit binding site is different from the binding site used by aminoglycosides, so there is no competition between the two.

Doxycycline has selective toxicity for prokaryotic cells, without damaging the dog’s eukaryotic cells.

Differences from other tetracyclines

Doxycycline is the most liposoluble drug within the tetracycline group. The active form of the molecule enters directly inside the infectious microbes through their lipid membrane.

Its strong ability to penetrate microorganisms reduces the number of antibiotic-resistant cases as it is effective where other tetracyclines fail.

Different pharmaceutical forms of doxycycline

Doxycycline is available in two pharmaceutical forms:

• Oral formats: 20, 100 and 300 mg tablets. There is also a powder formulation in a 260 mg sachet.
• Injectable format: 20 mg/mL, long acting.

The usual doses for doxycycline in dogs and cats are 10 mg/kg given orally with food every 24 hours, or 5 mg/kg given orally every 12 hours for 3 weeks in cats with chlamydiosis.

Pharmacokinetics of doxycycline in dogs

Doxycycline absorption is not affected by food in the digestive tract. Furthermore, it penetrates most tissues very efficiently because of its high liposolubility.

It has a high protein binding capacity and a plasma half-life of 18–24 hours, so it is considered a long-acting drug and therefore offers the advantage of only requiring one daily dose.

Doxycycline is mainly eliminated by the intestinal route, so it can still be indicated for patients with kidney failure.

Indications for doxycycline in dogs and cats

Doxycycline is used as a specific treatment for the following diseases:

• Bartonellosis caused by Haemobartonella felis and canis.
• Pneumonia and bronchopneumonia caused by Staphylococcus spp., Streptococcus spp., Haemophilus spp., Bordetella bronchiseptica andMycoplasma spp.
• Pharyngitis, tonsillitis, otitis, tracheitis, bronchitis and sinusitis caused by different strains of Streptococcus, Staphylococcus, Mycoplasma and Chlamydia.
• Genitourinary tract infections caused by Klebsiella, Staphylococcus spp., Streptococcus spp., Escherichia coli and Mycoplasma.
• Leptospirosis
• Borreliosis caused by Borrelia burgdorferi.
• Ehrlichiosis, tetanus and brucellosis
• Gastrointestinal infections caused by Escherichia coli, Salmonella spp. and Campylobacter jejuni.
• Skin infections, abscesses and cellulitis caused by Staphylococcus aureus and Streptococcus spp.
• Otitis caused by different Staphylococcus, Streptococcus, Mycoplasma and Chlamydia species.
• Postoperative prophylaxis or wounds infected with Staphylococcus spp., Streptococcus spp., Corynebacterium spp., Escherichia coli and Pasteurella multocida.
• Joint infections, arthritis and abscesses caused by Staphylococcus spp., Streptococcus spp. and Corynebacterium spp.
• Pododermatitis caused by Fusobacterium spp. or Staphylococcus spp.
• Periostitis and gingivitis caused by Fusobacterium, Streptococcus, Staphylococcus and Bacteroides.

Doxycycline in dogs and cats: side effects

Tetracyclines can have a negative impact on bone growth and development in animals. They may even stain the teeth if given to expectant mothers in the last 2–3 weeks of pregnancy or during the first few weeks of a puppy’s life. Doxycycline appears to cause fewer side effects than other tetracyclines because it does not bind to calcium as strongly.

Similarly, doxycycline should not be given to lactating females as significant amounts pass into breast milk and therefore onto the puppies. Otherwise it may cause the puppies problems such as dental hypoplasia, photosensitivity reactions and longitudinal bone growth inhibition.

Unlike in puppies, photosensitivity reactions are very rare in adult dogs.

Doxycycline administration routes

As we have already mentioned, the bioavailability of doxycycline is not affected by the presence of food. The tablets may be administered whole, crushed or even dissolved in some liquid. If the tablets are crushed and dissolved in a liquid, it must be ingested immediately.

If prescribed as a single daily dose, patients should be given 10 mg/kg; however, if the drug is administered every 12 hours, the dose should be 3–5 mg/kg.

Treatment duration

In the case of bartonellosis, ehrlichiosis, leptospirosis and brucellosis, the treatment is administered for at least 30 days according to the vet’s discretion. Dogs should be given 10 mg/kg/day and cats should receive 5–10 mg/kg/day.

Indications are for 5–10 mg/kg/day for 10–15 days to treat respiratory, genitourinary and intestinal infections.

Contraindications

• Doxycycline should not be given to pregnant dogs to avoid undesirable effects on the foetus.
• Nor should it be given to animals undergoing treatment with phenytoin or barbiturates.
• Do not administer doxycycline in combination with antacids as this alters its absorption.
• Adjust the doxycycline dose in patients with liver failure because its delayed metabolism may increase the drug’s half-life and cause toxicity.
• Doxycycline doses do not need to be adjusted in the case of kidney failure.