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Drug Details

  • Drug Name: Ampicillin
  • Common Name: Polyflex®
  • Drug Type: Beta-lactam antibiotics
  • Used For: Bacterial infections
  • Species: Dogs, Cats
  • Administered: 250 mg and 500 mg capsules, Oral liquid, Injection
  • How Dispensed: Prescription only
  • FDA Approved: Yes

General Description


Penicillin was the first antibiotic made available to humans during World War II. It was very effective against gram-positive bacteria, but didn’t last long and was susceptible to stomach acid so was wasted inside the body.


Ampicillin is a version of penicillin that is able to last longer, resist stomach acid, and kill some gram-negative bacteria as well as the gram-positive bacteria. It is often used to prevent and treat infections found in cuts and wounds, the mouth, the upper respiratory system, and the bladder.


Bacteria often build resistance to this drug.


This drug works best if given 1 hour before feeding or 2 hours after. It may be given with food is stomach upset occurs.
The oral form of this drug is not absorbed very effectively, as with the injection or Amoxicillin.


How It Works


Ampicillin kills bacteria by preventing them from building a proper cell wall while they grow. It accomplishes this by inhibiting the linking of peptidoglycan chains that are a major component in both gram-positive and some gram-negative bacteria’s cell walls.


Storage Information


Store tablets in a tightly sealed container at room temperature.


Keep oral liquid refrigerated- effective 14 days after mixed.


Injection is effective 3 months after reconstitution at room temperature and 1 year after reconstitution if refrigerated.


Ampicillin sodium Injection should be used immediately after reconstitution.


Missed Dose?


Give the dose as soon as possible. If it is almost time for the next dose, skip the missed dose, and continue with the regular schedule. Do not give your pet two doses at once.


Side Effects and Drug Reactions


Ampicillin may result in these side effects:

  • Allergic reaction (labored breathing, hives, etc)
  • Loss of appetite
  • Drooling
  • Vomiting/Nausea
  • Diarrhea


Ampicillin may react with these drugs:

  • Cephalosporin
  • Antacids
  • Aminoglycosides
  • Bacteriostatics (Drugs that inhibit bacterial growth)
  • Allopurinol



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