Updated 11 February 2013


Ampicillin is also one of multiple active ingredients found in Ampicloc, Apen, Cloxam and Megamox.


Ampicillin is the active ingredient of Ampicillin-Fresenius, Ampipen, Be-Ampicil, Penbritin, Petercillin, Ranamp and Spectracil.

Ampicillin is also one of multiple active ingredients found in Ampicloc, Apen, Cloxam and Megamox.

General information

Ampicillin is a penicillin antibiotic. It is prescribed for the treatment of a wide range of bacterial infections caused by susceptible organisms including middle ear infections, upper and lower respiratory tract infections, and gastro-intestinal infections.

Ampicillin can cause minor stomach upsets and a blotchy skin rash, a common unwanted effect, which is not necessarily an indication of an allergic reaction. Should you develop a skin rash, you should consult your doctor to rule out the possibility of allergy. A penicillin allergy may lead to fever, swelling of the mouth and tongue, itching and associated breathing difficulties.

It is important to note that this medication is only effective against bacterial infections - if your infection is the result of a viral or fungal infection it will be ineffective.

Antibiotic resistance - when bacteria develop the ability to defend themselves against the effect of an antibiotic - occurs frequently with many antibiotics. The most common causes for this is when patients do not complete the prescribed course in full, allowing infections to recover from treatment, and by using antibiotics for non-bacterial infections such as cold and flu.

Oral contraceptives may not be as effective as usual while taking ampicillin - other methods of contraception are advised to avoid unplanned pregnancy.

How does ampicillin work?

Ampicillin functions by changing the structure of the bacterial cell wall allowing fluid to penetrate into the cell. As a result the bacterial cell literally ruptures.

Fast facts

Drug schedule: schedule 4

Available as: ampicillin is available as capsules, oral suspension and injection

What does it do? Ampicillin is an antibiotic

Overdose risk: low

Dependence risk: low

Is ampicillin available as a generic? yes

Is ampicillin available on prescription only? yes

User information

Onset of effect: rapid - within 2 hours

Duration of action: up to 8 hours

Dietary advice: ampicillin can be taken with or without food. Taking it with a meal may however minimise stomach irritation, diarrhoea and nausea.

Stopping this medicine: complete the full course as prescribed by your doctor, even if you feel better within a few days. Premature discontinuation may cause symptoms to recur, or cause bacterial resistance.

Prolonged use: ampicillin is generally given as short courses only - prolonged use may increase the risk of a medicine-resistant infection.

Special precautions

Consult your doctor before using this drug if:

  • you are allergic to either penicillin or cephalosporins antibiotics as there is a

possibility that you may be allergic to Ampicillin as well

  • you have kidney or liver disease
  • you have inflammatory bowel disease or ulcerative colitis
  • you have any allergies
  • you have glandular fever
  • you have leukaemia
  • you are taking other medications

Pregnancy: this medication is considered safe. You should however still consult your doctor before use.

Breastfeeding: avoid. This medication is passed through breast milk and may affect your baby adversely. Consult your doctor before use.

Porphyria: this medication is safe use.

Infants and children: this medication is safe for use in children at the recommended dose.

The elderly: no special precautions need to be taken.

Driving and hazardous work: no special precautions need to be taken.

Alcohol: no special precautions need to be taken.

Possible side effects

Side effect


Consult your doctor



Only if severe

In all cases

mild diarrhoea



nausea/ vomiting






white patches on tongue/ vaginal discharge/itch



skin rash/ itch






swollen mouth/ tongue






unusual bruising






dizziness/ fainting




Drug interactions:


increased risk of skin rash


may affect the efficacy of ampicillin. Take at least 2 hours apart.


reduce the efficacy of ampicillin

oral contraceptives

possible reduced contraceptive efficacy. Another form of contraceptive is advised.


increased risk of ampicillin toxicity


possible reduced ampicillin efficacy


increased risk of warfarin toxicity

Overdose action

A small overdose is no cause for concern. In case of intentional large overdose, seek emergency medical attention.

Recommended dosage

Adults: 250-500 mg every 6 hours

Children under 20 kg: 10-25 mg/kg 6 hourly

Children over 20 kg: as for adults

This material is not intended to substitute medical advice, but is for informational purposes only. Please consult a physician for specific treatment and recommendations.


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