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Category: Antibiotics
Commercial name: Ampicillin
Active ingredient: Penicillin
Production form: Pills
Available dosage: 250 mg, 500 mg

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Ampicillin (Penicillin). Dosage, Side Effects, Interactions

The beta-lactam antibiotic Ampicillin (Penicillin) comes from the group of penicillins with an extended spectrum of action. The active ingredient selectively inhibits bacterial cell wall synthesis and thus has a bactericidal effect. It is used orally or parenterally to treat various bacterial infections.

Ampicillin is a penicillin antibiotic and thus belongs to the active substance group of beta-lactam antibiotics with an extended spectrum of action. Due to structural modifications, the active ingredient is acid-stable and can therefore be used in infections of the following pathogen spectrum.

  • Gram-positive cocci (such as streptococci, including pneumococci)
  • Enterococci (such as Escherichia faecalis)
  • Listeria
  • Gram-positive rods (aerobic like diphtheria bacteria, anaerobic like Clostridium tetani)
  • Gram-negative cocci (such as meningococci)
  • Spirochetes (such as Borrelia burgdorferi)
  • Gram-negative rods (such as Escherichia coli, Haemophilus influenzae)

Ampicillin can be used orally to treat the following bacterial infections.

  • Acute bacterial sinusitis after adequate diagnosis
  • Acute otitis media
  • Acute exacerbations of chronic bronchitis after adequate diagnosis
  • Community-acquired pneumonia
  • urocystitis
  • Infections of the gallbladder and bile ducts
  • Infections of the gastrointestinal tract
  • Skin and soft tissue infections
  • Infections around the eyes
  • listeriosis
  • Osteomyelitis at the stage of oral follow-up treatment

Parenteral therapy is preferable to oral therapy in the case of severe clinical pictures and the following additional indication areas.

  • Infections of the genitals
  • Meningitis , endocarditis, sepsis and osteomyelitis, particularly in the case of ampicillin-sensitive Haemophilus influenzae, enterococci and listeria, if necessary in combination with another suitable antibiotic

In combination with the beta-lactamase inhibitor sulbactam , ampicillin is used in addition to infection prophylaxis after major surgical interventions in the following body regions:

  • gastrointestinal tract
  • pelvic cavity
  • head and neck
  • biliary tract

Application type

Ampicillin is commercially available in tablet and injectable form. The combination of ampicillin with the beta-lactamase inhibitor sulbactam is available as a powder that is made up into a solution for injection. Parenteral application is intramuscular or intravenous as a short or continuous drip infusion.


How Ampicillin (Penicillin) works

Ampicillin is a beta-lactam antibiotic that selectively inhibits bacterial cell wall synthesis and is bactericidal.

The bacterial cell wall contains what is known as murein, a layer of cross-linked peptidoglycans that are made up in particular of N-acetylglucosamine and N-acetylmuramic acid. The cross-linking of the peptide chains is catalyzed by transpeptidases, which cleave a bond between D-alanine and D-alanine and use the resulting energy to transfer amino acids. Beta-lactam antibiotics such as ampicillin are structural analogues of D-alanine-D-alanine. They inhibit the bacterial transpeptidase pseudo-irreversibly by forming a significantly more stable bond than the natural substrate, which is only cleaved very slowly. In this way, the integrity and stability of the peptidoglycans in proliferating pathogens is severely disrupted, resulting in growth inhibition and ultimately cell lysis.

The spectrum of activity of ampicillin depends on the structure of the bacterial cell wall of the various species, the enzyme activity and the ability of the active ingredient to penetrate. Due to structural modifications, ampicillin is acid-stable and has an extended spectrum of activity against certain gram-negative germs. Because ampicillin is beta-lactamase-labile, it is also used in combination with the beta-lactamase inhibitor sulbactam, which prevents ampicillin from being broken down by these bacterial enzymes.




Ampicillin is only moderately absorbed when administered orally. The reason for this is the pH-dependent polarity of the active substance. Ampicillin is present throughout the gastrointestinal tract as a poorly absorbed ionic structure. The cation is formed at the gastric pH, a zwitterion is formed in the intestine and in later stages the deprotonated anion. However, ampicillin is partially actively absorbed, so that the bioavailability is 30 to 60%. Simultaneous food intake impairs absorption. Maximum plasma levels of 5 mg/l are reached after 90 to 120 minutes after oral administration of 1000 mg ampicillin, and after 30 to 60 minutes after intramuscular administration. The bioavailability with intramuscular administration is almost complete, but is even further increased with intravenous administration.


Ampicillin has good tissue penetration. A low diffusion is achieved in muscles, bones and liquor. In the case of inflamed meninges, the CSF permeability can be increased by up to 50%. The plasma protein binding of ampicillin is 17 to 20%, the apparent volume of distribution is approximately 15 L.


About 10% of ampicillin is metabolised to inactive penicilloates.


About 40% of the beta-lactam is eliminated unchanged after oral administration or 73% after parenteral administration via the kidneys. Ampicillin undergoes glomerular filtration but is also subject to active tubular secretion. After intravenous administration, renal clearance is approximately 194 ml/min. Ampicillin continues to be excreted in the faeces. The half-life is one to two hours.

The elimination half-life can be prolonged to 8 to 20 hours in renal insufficiency and to 2 to 4 hours in neonates.


Dosage of Ampicillin (Penicillin)

The dosage of ampicillin depends on the age, weight and renal function of the patient, the severity and location of the infection and the suspected or proven pathogens.

Ampicillin is administered orally from the age of 6 years, three times a day at eight-hour intervals or four times a day at six-hour intervals, whole with sufficient liquid on an empty stomach. The usual dosage is 2 to 6 g of ampicillin per day.

The usual dose for parenteral administration of the antibiotic from the age of 6 years is 1.5 to 6 g ampicillin, the daily dose can be increased to up to 15 g. Here, too, a dosing interval of three to four times a day is usual, in rare cases twice a day is sufficient. The injection time should not exceed three minutes per 1 g of ampicillin.

Injection solutions containing a combination of ampicillin and the beta-lactamase inhibitor sulbactam are used in adolescents and adults in doses of 1.5 to 3 g (1 g ampicillin and 0.5 g sulbactam to 2 g ampicillin and 1 g sulbactam) every six used for up to eight hours. The maximum daily dose is 12 g solution for injection, which corresponds to 8 g ampicillin and 4 g sulbactam. Children and newborns receive a daily dose of 150 mg of the solution for injection (100 mg ampicillin and 50 mg sulbactam) per kilogram of body weight. This dose is divided into three to four doses for children and two doses for newborns.

Dose reduction is required in moderate to severely impaired renal function. If the creatinine clearance is between 20 and 30 ml/min, the dose is reduced to 2/3 of the normal dose. If the creatinine clearance is below 20 ml/min, the dose is reduced to 1/3 of the normal dose. In the case of impaired renal function, a maximum of 1 g of ampicillin should be administered in 8 hours.

Duration of use

The duration of the application depends on the course of the disease and is usually between seven and ten days. Ampicillin should be taken for at least two to three days after the symptoms have subsided. Injection solutions with ampicillin and sulbactam for prophylaxis after surgical interventions are given at the beginning of anesthesia. The injection can be repeated after six to eight hours, and prophylaxis is usually ended after 24 hours.


Side effects of Ampicillin (Penicillin)

The following undesirable effects occur frequently (≥ 1/100 to < 1/10) to very frequently (≥ 1/10) when using ampicillin:

  • diarrhea
  • Nausea, abdominal pain, meteorism
  • Allergic reactions ranging from mild skin symptoms such as exanthema and itching to occasionally severe allergic reactions such as anaphylactic shock
  • Typical maculo-papular exanthema can appear five to ten days after the start of treatment. These reactions are not allergic and usually disappear with continued therapy.

Bacteria can develop resistance mechanisms over time that prevent ampicillin from working. These include:

  • Inactivation by beta-lactamases
  • Reduced affinity of penicillin-binding proteins due to mutations
  • Inadequate penetration of ampicillin through the outer cell wall, especially in gram-negative pathogens
  • Efflux pumps that pump ampicillin out of bacterial cells

There is a risk of cross-resistance with amoxicillin and sometimes also with other penicillins and cephalosporins. An antigen community can also exist between fungi and ampicillin, so that in the case of pre-existing mycosis, allergic reactions can occur when ampicillin is administered for the first time.



When ampicillin is used in combination with the active substances below, the following interactions can occur:

  • Probenecid , NSAIDs ( acetylsalicylic acid , indomethacin , phenylbutazone ): competition for active tubular secretion, increased plasma levels and half-life of the penicillins and also beta-lactamase inhibitors
  • Methotrexate : Reduced elimination and thus increased toxicity of methotrexate, therefore longer administration and increased dosage of the active folic acid metabolite leucovorin as well as close monitoring necessary
  • Digoxin : increased absorption
  • Allopurinol : increased risk of skin rashes
  • Anticoagulants : additive anticoagulant effects
  • Bacteriostatic drugs ( chloramphenicol , erythromycin , sulfonamides, tetracyclines ): impairment of the bactericidal effect of ampicillin
  • Estrogen-containing oral contraceptives : possibly reduced effectiveness and thus unplanned pregnancy possible (so far only limited evidence of a causal relationship is available)


When using Ampicillin there are the following contraindications:

  • Hypersensitivity to the active substance or other penicillins
  • Intramuscular application in infants and small children under two years of age


In pregnant women, the plasma concentration of ampicillin can be reduced by up to 50%. The active substance can penetrate the placenta, but so far there have been no signs of teratogenic effects. However, the experience to date is insufficient and there is no experience of the use of ampicillin in the first trimester. No reproductive-toxic properties were found in animal experiments. As a precaution, ampicillin should only be used during pregnancy after a careful risk-benefit assessment.



Ampicillin passes into breast milk, which can lead to diarrhea and sprout colonization of the mucous membranes in infants. Furthermore, sensitization is possible. For these reasons, it may be necessary to stop breastfeeding during therapy with ampicillin. In general, however, ampicillin can be used during breastfeeding after careful benefit-risk assessment.


Driving ability

Ampicillin has no effect on the ability to concentrate and react. However, it should be borne in mind that in isolated cases dizziness and light-headedness may occur.

Further information can be found in the respective technical information.

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Additional information


250 mg, 500 mg


30, 60, 90, 120, 180


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