By Kayla Hyland, DVM; Rania Gollakner, BS, DVM, MPH

What is ampicillin?

Ampicillin (brand names: Omni-Pen®, Teva-ampicillin®, Polyflex, Aminopenicillin®, Principen®, Princillin®, Totacillin®) is an antibacterial medication used to treat certain bacterial infections in small and large animals.

Its use in cats, dogs, reptiles, and other small animals to treat certain conditions is “off label” or “extra-label”. Many drugs are commonly prescribed for off-label use in veterinary medicine. In these instances, follow your veterinarian’s directions and cautions very carefully as they may be significantly different from those on the label.

How is ampicillin given?

Ampicillin trihydrate injection is given under the skin or into the muscle but should not be given into the vein, as this can cause sudden death. If giving subcutaneous injections at home, use a new needle and syringe for each injection, and dispose of the needle and syringe into a proper sharps disposal container. Ampicillin sodium is given in the hospital by injection into the vein (IV).

Ampicillin is also available as a liquid oral solution, tablet, or capsule and is given by mouth. If given by mouth, give on an empty stomach at least 1 hour before or 2 hours after feeding. If vomiting occurs after dosing on an empty stomach, try giving future doses with food or a small treat.

This medication will take effect quickly, in about 1 to 2 hours, but effects may not be obvious for a few days.

What if I miss giving my pet the medication?

If you miss a dose, give it when you remember. However, if it is close to the time for the next dose, skip the dose you missed, give it at the next scheduled time, and return to the regular dosing schedule. Never give your pet two doses at once or give extra doses.

Are there any potential side effects?

Side effects are not common, but may include allergic reaction, lack of appetite, pain at the injection site, vomiting, and diarrhea. In dogs, incoordination is associated with very high doses. Increased breathing rate, breathing problems, swelling, increased heart rate, and elevated liver values on bloodwork have been reported. In cats, if there is a complete loss of appetite, contact your veterinarian immediately. Ampicillin can also cause false positives with certain urine glucose tests.

This short-acting medication should stop working within 24 hours, although effects can be longer in pets with liver or kidney disease.

Are there any risk factors for this medication?

Ampicillin should not be used in patients that are hypersensitive to penicillin-type antibiotics and should be used with caution in patients that are hypersensitive to beta-lactam antibiotics. Avoid using this medication in rabbits, guinea pigs, chinchillas, or hamsters

Using ampicillin during pregnancy and lactation has not been shown to be problematic, but it has not been clearly established as safe. Therefore, ampicillin should be used with caution in pregnant or lactating pets, and only used when the benefits will outweigh the risks.

Are there any drug interactions I should be aware of?

The following medications should be used with caution when given with ampicillin: allopurinol, aminoglycosides, atenolol, bacteriostatic antimicrobials, dichlorphenamide, lanthanum, methotrexate, mycophenolate, pantoprazole, probenecid, venlafaxine, and warfarin.

Tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking.

Is there any monitoring that needs to be done with this medication?

There is no specific monitoring that needs to be done while your pet is taking this medication. Your veterinarian may monitor your pet to be sure that the medication is working.

How do I store ampicillin?

Ampicillin trihydrate powder should be stored below 25°C (77°F) with trips permitted up to 30°C (86°F), and the reconstituted suspension should be stored for up to 3 months in the refrigerator between 2°C and 8°C (36°F to 46°F). Tablets, capsules, and powder for oral use should be stored at room temperature between 15°C and 30°C (59°F to 86°F). Once reconstituted, the oral suspension should be stored in the refrigerator and discarded after 14 days. It may be stored at room temperature, but in these cases, it should be discarded after 7 days.

What should I do in case of emergency?

If you suspect an overdose or an adverse reaction to the medication, call your veterinary office immediately. If they are not available, follow their directions for contacting an emergency facility.

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