Antibiotics for Cat Diarrhea

Ampicillin and Amoxicillin

• Ampicillin and amoxicillin are part of the penicillin family and may be used as a first-line antibiotic in simple diarrhea cases. They are active against many organisms, including salmonella, but not bacteria that produce enzymes to break down the antibiotic, such as E. coli and some of the staphylococcus species. Amoxicillin is frequently given in a palatable combination tablet with the drug clavulanic acid, which makes the tablet more potent and effective against a greater number of bacterial species. The most common side effect with these drugs is vomiting, but because this occurs in less than 1 percent of cats treated, it remains a favorite of many veterinarians.

Erythromicin

• Erythromicin works like many of the penicillin drugs but is specifically active against the campylobacter species of bacteria. Your veterinarian will usually use this only when he has a specific diagnosis from a fecal sample. It can be a tricky bug to diagnose, and you may have to collect samples on alternate days for a week to be sure. Your veterinarian will then medicate your cat at a higher than normal dose rate for five to 10 days. The most common side effect with erythromicin is vomiting, and the drug is not commonly used in cats with diagnosed liver dysfunctions.

Metronidazole

• Metronidazole can be used to treat simple bacterial diarrheas and those that have more unusual causes. Giardia is a single-celled, or protozoan, parasite that cats can carry in their intestines without showing symptoms. This means that giardia can be spread without the owner's knowledge in multi-cat households or just when cats are socializing around the neighborhood. In the unlucky cats that show signs of infection, particularly kittens or cats unwell for other reasons, the parasite causes an intermittent or continuous diarrhea. This can make giardia difficult to diagnose but, once it's identified as the cause of diarrhea, all the cats in the household can be readily treated with metronidazole at a higher than usual dose rate given once daily for five days.

  Metronidazole also may be used to treat bacterial overgrowth in the small intestine where pathogenic bacteria have overwhelmed the normally friendly bacteria of the gut. This requires a prolonged regular dose of metronidazole to help restore the balance. Some of the diarrhea cases related to allergies or sensitivities can be treated with metronidazole alongside steroids, because the antibiotic helps reduce the body’s response to the allergen and so speeds healing.

  Adverse effects are usually rare in the cat but may include vomiting, nervous signs such as staggering or seizures, liver problems or urinary symptoms. Metronidazole is not given during the first trimester of pregnancy because it may cause birth defects.

Sulfonamides

• Sulfonamides are frequently given in combination with trimethoprim, creating a more effective drug to which bacterial resistance develops slowly. Many bacteria, including salmonella, and parasitic organisms such as toxoplasma are susceptible to trimethoprim sulfonamides. These drugs are most commonly used in treating the diarrhea caused by these parasites and are administered for up to three weeks. However, the side effects of the trimethoprim sulfonamides can be serious. A cat may show an acute hypersensitivity reaction, develop anorexia, or suffer a reduction in either its white or red blood cell count, leading to further illness.

Tetracyclines

• The tetracyclines, including oxytetracycline and doxycycline, are most commonly given to treat campylobacter or a bacterial overgrowth of pathogenic bacteria in the small intestine. They are considered safe drugs with few side effects and are often used in cats with reduced kidney function.

Tylosin

• Tylosin is rarely used in cat medicine but is sometimes the drug of choice in chronic infections of the colon or lower bowel.