Gastrointestinal, liver effects common after doxycycline in cats

By Sarah Guy, medwireNews Reporter

Doxycycline, an antibiotic derivative of tetracycline, commonly results in adverse gastrointestinal side effects and increased liver enzyme activity in cats, report German researchers.

More than 10% of cats in their study developed vomiting and/or diarrhea following treatment with the drug, and of those tested, up to 18% of animals also showed changes in alanine aminotransferase (ALT) activity, says the team.

The findings indicate a need to "carefully monitor" cats being treated with doxycycline, suggest Bianka Schulz (Ludwig Maximilian University Munich) and colleagues in Veterinary Record.

They identified 168 cats treated with the antibiotic between 2000 and 2007 and investigated possible correlations between factors including gender, age, clinical signs such as ALT and alkaline phosphatase (ALP) activity, and adverse side effects.

Cats were aged a mean of 6.8 years, and 47.6% were female or female-spayed. The remainder were male or male-spayed. The most common indications for doxycycline were infections with hemotrophic mycoplasmas and respiratory tract infections, and the animals received doses ranging from 2 to 24 mg/kg per day.

Overall, 12.8% of animals developed vomiting symptoms while receiving doxycycline therapy and the risk for vomiting increased 5.35-fold if gastric protectants and/or antiemetics were given alongside the antibiotic.

Diarrhea developed in 10.9% of cats during therapy, with male cats having 4.07 times the risk for this side effect compared with their female counterparts. Previous laboratory studies suggest this gender difference could be a result of sex-related differences in cytochrome-p450-enzyme expression, note Schulz et al.

Anorexia developed in 6.1% of cats, and 7.2% developed fever. Cats given glucocorticoids in addition to doxycycline had a significant 15.49-fold increased risk for developing fever compared with those that received doxycycline alone.

Pre-therapy ALT levels were normal in 110 cats, and 43 were re-measured during doxycycline treatment. Of these, 18.6% had increased ALT activity at between two- and fourfold the reference range.

Of the 51 cats whose ALP activity was normal before doxycycline and re-measured, 5.9% had developed a twofold increase from the reference range after treatment, note the authors.

Possible mechanisms for these potentially damaging increases in liver function markers include disturbances of ß-oxidation, the citric-acid cycle, oxidative phosphorylation, and protein biosynthesis, they conclude.

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