(ampicillin, ampicillin sodium, ampicillin trihydrate)


Veterinary: Polyflex

Veterinary Availability:

  • Polyflex (ampicillin trihydrate powder for suspension) 10 gm, 25 gm


Human: Novo Ampicillin (ampicillin), Ampicin (ampicillin sodium), Principen (ampicillin trihydrate)

Human Availability:

  • Ampicillin sodium tablets: 500 mg
  • Ampicillin trihydrate Capsules: 250 mg, 500 mg
  • Ampicillin trihydrate powder for oral suspension: 125 mg/5mL, 250 mg/5mL
  • Ampicillin sodium powder for Injectable: 250 mg, 500 mg vials


Ampicillin, a beta-lactam semi-synthetic aminopenicillin, acts as a bactericidal agent against microorganisms by inhibiting cell wall synthesis during active multiplication.

The aminopenicillins (also called broad-spectrum antibiotics) have shown to be active against most strains of Gram-positive aerobes such as: Enterococcus faecalis, beta -lactamase-negative strains of the Staphylococcus spp., Streptococcus pneumoniae, and the alpha and beta-hemolytic strains of streptococcus. They have increased activity against some strains of Gram-negative aerobes such as E. coli, klebsiella and haemophilus. They also show some activity against anaerobic bacteria such as clostridial organisms.
Aminopenicillins can be inactivated by beta-lactamase-producing bacteria such as Staphylococcus aureus. Those organisms that are generally not susceptible to the aminopenicillins are Pseudomonas aeruginosa, serratia, enterobacter, acinetobacter, citrobacter and also rickettsia, mycobacteria, fungi, mycoplasma, and viruses.

Ampicillin is widely distributed into many tissues and fluids, including cerebrospinal fluid in the presence of inflamed meninges. It is found to cross the placenta and be excreted in small concentration in breast milk; however, it is believed to be safe for use during pregnancy and lactation.

It is eliminated through renal mechanisms by way of tubular secretion and primarily excreted in urine.


Useful in systemic infections, acute and chronic urinary tract infections, as well as skin and skin structure infections.

Drug Interactions or Contraindications:

  • Concomitant use of Probenecid will increase the plasma level of ampicillin.
  • Since in septicemia or shock gastrointestinal absorption is reduced it is advised to administer by parenteral route rather than oral.

Adverse Reactions

Blood: anemias

GI: anorexia,diarrhea

Other: hypersensitivity reaction such as rash and itching. Prolonged high doses can cause neurotoxicity. When given orally the penicillin’s may alter gut flora, selecting out resistant bacteria residing in the colon (leading to superinfections).

Dosage Recommendations

20 mg/kg to 100 mg/kg total dose to be divided over q8h; PO or SQ for 7 to 14 days  2


20 mg/kg to 100 mg/kg, PO, SQ, IM, q12hr  1, 27


20 mg/kg to 100 mg/kg, PO, SQ, IM, q8hr  35


25 mg/kg, SQ, IM, q12hr  41, 42, 44


20 mg/kg to 250 mg/kg, PO, q12hr  41, 44


50 mg/kg to 200 mg/kg, PO, q12hr  41, 42, 44


  • Drug recommendation is to give on empty stomach (1 to 2 hours before meal or 2 hours after meals) to prevent interference with absorption of the antibiotic.
    Some drugs are known to be better absorbed without food, but unless a rat is in a hospital environment, we realize that this is impossible for the pet rat owner. It is believed to be far more important to get the medication into the rat, even if you have to mix it in a favorite food, than to worry about whether food will hinder the medications absorption rate.
  • Give yogurt, Lactobacillus capsules/granules, or Bene-Bac to help maintain normal gut flora.
  • In treating suspected polymicrobial infections, where a broader coverage may be needed, synergistic or combination drugs may be used. The following drugs may be seen used simultaneously with ampicillin: aminoglycosides (e.g., amikacin or gentamicin), or cephalosporin, or fluoroquinolones (e.g., enrofloxacin or orbifloxicin). 1
  • Please note that it is imperative to discuss the changing or adding of any medications during your rat’s treatment with your veterinarian to prevent future resistance of microbes to the drugs prescribed.
  • Store capsules at room temperature.
  • Reconstituted oral suspensions are good for 14 days if refrigerated and for 7 days if left at room temperature.


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