15–20%. Ampicillin is distributed through most tissues, though it is concentrated in the liver and kidneys. It can also be found in the cerebrospinal fluid when the meninges become inflamed (such as, for example, meningitis). Some ampicillin is metabolized by hydrolyzing the beta-lactam ring to penicilloic acid, though most of it is excreted unchanged. In the kidneys, it is filtered out mostly by tubular secretion; some also undergoes glomerular filtration, and the rest is excreted in the feces and bile. Hetacillin and pivampicillin are ampicillin esters that have been developed to increase bioavailability. History Ampicillin has been used extensively to treat bacterial infections since 1961. Until the introduction of ampicillin by the British company Beecham, penicillin therapies had only been effective against gram-positive organisms such as staphylococci and streptococci. Ampicillin (originally branded as "Penbritin") also demonstrated activity against gram-negative organisms such as H. influenzae, coliforms, and Proteus spp. Cost Ampicillin is relatively inexpensive. In the United States, it is available as a generic medication. Veterinary use In veterinary medicine, ampicillin is used in cats, dogs, and farm animals to treat: Anal gland infections Cutaneous infections, such as abscesses, cellulitis, and pustular dermatitis E. coli and Salmonella infections in cattle, sheep, and goats (oral form). Ampicillin use for this purpose had declined as bacterial resistance has increased. Mastitis in sows Mixed aerobic–anaerobic infections, such as from cat bites Multidrug-resistant Enterococcus faecalis and E. faecium Prophylactic use in poultry against Salmonella and sepsis from E. coli or Staphylococcus aureus Respiratory tract infections, including tonsilitis, bovine respiratory disease, shipping fever, bronchopneumonia, and calf and bovine pneumonia Urinary tract infections in dogs Horses are generally not treated with ampicillin, as they have low bioavailability of beta-lactams. The half-life in animals is around that same of that in humans (just over an hour). Oral absorption is less than 50% in cats and dogs, and less than 4% in horses. See also Amoxycillin (p-hydroxy metabolite of ampicillin) Azlocillin and pirbenicillin (urea and amide made from ampicillin) Pivampicillin (special pro-drug of ampicillin) References External links Enantiopure drugs Penicillins Phenyl compounds World Health Organization essential medicines Wikipedia medicine articles ready to translate