Penicillins (Oral)

Medication Information Leaflet

What is this medication for?

Penicillins are antibiotics that are used to treat and prevent a wide variety of bacterial infections. It works by stopping the growth of bacteria.

Examples of penicillins include:

  • Amoxicillin

  • Amoxicillin with Clavulanic acid

  • Cloxacillin

  • Penicillin V

How should I take/use this medication?

  • Amoxicillin and Amoxicillin with Clavulanic acid: Take this medication with or after food.

  • Cloxacillin and Penicillin V: Take this medication half to one hour before food.

  • You should complete each course of antibiotics even if you feel better as incomplete treatment might cause the infection to return or cause antibiotic resistance. When antibiotic resistance happens, the antibiotic will not be able to control the growth or kill the bacteria anymore.

  • Do not stop taking your medication without checking with your healthcare professional.

What should I do if I forget to take/use this medication?

If you forget to take a dose, take it as soon as you remember. Then take your next dose at the usual time. Do not take two doses to make up for the missed dose.

What precautions should I take?

Inform your healthcare professional if:

  • You had a previous allergic reaction to Amoxicillin, Cloxacillin, Cephalexin, Cefuroxime or other beta lactam antibiotics.

  • You are taking any other medications, including supplements, traditional medications and herbal remedies.

  • You have kidney problems.

  • You are pregnant, planning to become pregnant, or breastfeeding.

What are some common side-effects of this medication?

Some common side effects include:

  • Diarrhoea

  • Nausea, vomiting

  • Stomach upset or discomfort

Although uncommon, you may develop a black, "hairy" tongue while taking Penicillin. This effect is harmless and usually goes away after treatment. Maintain good oral hygiene and brush your tongue with a soft toothbrush twice a day.

If any of the side effects do not go away or are serious, please see your doctor.

What are some rare but serious side-effects that I need to seek medical advice immediately?

  • Vaginal itch or discharge, white spots on lips or in mouth

    • This may indicate a yeast infection which may need treatment.
  • Persistent diarrhoea, abdominal or stomach pain/cramp, blood/mucus in your stool

    • This could suggest a severe intestinal condition (pseudomembranous colitis). This condition may occur during the course of this medication or weeks after this medication has stopped. Do not use anti-diarrhoea products or narcotic pain medications if you have the symptoms because these products may make them worse.
  • The symptoms of a drug allergy include one or more of the following:

    • Swollen face/eyes/lips/tongue

    • Difficulty in breathing

    • Itchy skin rashes over your whole body

    • Sores in the mouth, red painful eyes or blisters on the skin

If you experience any of these symptoms, you should stop your medication and see your healthcare professional immediately.

What food or medication should I avoid when I take this medication?

  • Space this medication 2 hours apart from probiotics.

  • Inform your doctor if you are taking any other medications such as Methotrexate, antibiotics (e.g. Tetracyclines), blood thinners (e.g. Warfarin), Probenecid, and oral contraceptives.

How should I store this medication?

  • Store in a cool and dry place, away from direct sunlight. Keep this medication away from children.
  • For syrups, follow the instructions on the label regarding the expiry date and on the need for refrigeration of the syrup. Do not freeze. Discard any unused portion after the duration as stated on the label.

How should I throw away this medication safely?

Pack this medication into a black trash bag and seal it tightly before throwing into the rubbish chute or bin.


If you take more than the recommended dose, please seek medical advice immediately. The information provided on this page does not replace information from your healthcare professional. Please consult your healthcare professional for more information.

This article is jointly developed by members of the National Medication Information workgroup. The workgroup consists of cluster partners (National Healthcare Group, National University Health System and SingHealth), community pharmacies (Guardian, Unity and Watsons) and Pharmaceutical Society of Singapore. The content does not reflect drug availability and supply information in pharmacies and healthcare institutions. You are advised to check with the respective institutions for such information.

Last updated on Apr 2021

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