How does this medication work? What will it do for me?

Penicillin belongs to the family of medications known as antibiotics. Penicillin is used to treat infections caused by certain bacteria. It is most commonly used to treat certain throat, respiratory tract, and skin infections. It may be used to prevent certain infections in people whose body is unable to fight infections. It works by killing or preventing the growth of bacteria that cause the infection.

Your doctor may have suggested this medication for conditions other than the ones listed in these drug information articles. As well, some forms of this medication may not be used for all of the conditions discussed here. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

What form(s) does this medication come in?

Oral Solution

125 mg
After reconstitution, each 5 mL pink, cherry-flavoured suspension contains penicillin V potassium 125 mg (200,000 IU). Nonmedicinal ingredients: artificial cherry flavour, FD&C Red No. 40, sodium benzoate, sodium citrate, sodium cyclamate, and sucrose.

300 mg
After reconstitution, each 5 mL pink, cherry-flavoured suspension contains penicillin V potassium 300 mg (500,000 IU). Nonmedicinal ingredients: artificial cherry flavour, FD&C Red No. 40, sodium benzoate, sodium citrate, sodium cyclamate, and sucrose.


Each orange, film-coated, round, biconvex, scored tablet identified "APO" over "300" on one side, contains penicillin V potassium 300 mg (500,000 IU). Nonmedicinal ingredients: colloidal silicon dioxide, croscarmellose sodium, FD&C Yellow No. 10 Aluminum Lake, FD&C Yellow No. 6 Aluminum Lake, hydroxypropyl cellulose, magnesium stearate, methylcellulose, polyethylene glycol 8000, and titanium dioxide.

How should I use this medication?

The recommended dose of penicillin for adults and children varies according to the infection being treated. The recommended dose for adults and children more than 12 years old ranges between 1 to 4 grams daily, divided into 3 to 4 doses.

The dose for children under 12 years old is based on body weight. The recommended daily dose varies between 25 mg and 100 mg per kg of body weight and is divided into 3 or 4 equal doses.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

The liquid form of this medication should be measured accurately with a medication spoon or oral syringe. Shake the bottle of liquid penicillin well before measuring each dose.

When taken by mouth, penicillin should be taken on an empty stomach, either 1 hour before or 2 hours after meals.

Finish all this medication, even if you have started to feel better. This will reduce the chance of the infection returning.

It is important to take this medication exactly as prescribed by your doctor. If you miss a dose, take it as soon as possible and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store penicillin tablets at room temperature and penicillin solution in the refrigerator. Keep this medication out of the reach of children.

Do not dispose of medications in wastewater (e.g. down the sink or in the toilet) or in household garbage. Ask your pharmacist how to dispose of medications that are no longer needed or have expired.

Who should NOT take this medication?

Do not take this medication if you:

  • are allergic to penicillin or any ingredients of the medication.
  • have certain types of severe infections

What side effects are possible with this medication?

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

  • diarrhea
  • nausea
  • skin rash
  • stomach pains
  • vomiting

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

  • blood in the urine
  • fever, itchy skin, muscle pain, swollen glands, general feeling of unwellness
  • signs of liver problems, e.g.:
    • dark urine
    • diarrhea
    • loss of appetite
    • nausea
    • pale stools
    • vomiting
    • weight loss
    • yellowing of the skin or whites of the eyes

Stop taking the medication and seek immediate medical attention if any of the following occur:

  • diarrhea (watery and severe; may also be bloody)
  • fever that appears after starting the antibiotic
  • seizures
  • signs of a serious allergic reaction, e.g.
    • abdominal cramps
    • difficulty breathing
    • nausea and vomiting
    • swelling of the face and throat
  • signs of a severe skin reaction, e.g.:
    • a rash combined with fever or discomfort
    • a rash covering a large area of the body
    • a rash that spreads quickly
    • blistering
    • peeling

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Are there any other precautions or warnings for this medication?

Before you begin taking a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should take this medication.

Allergy: Some people who are allergic to cephalosporin antibiotics also experience allergic reactions to penicillin. Before you take penicillin, inform your doctor about any previous adverse reactions you have had to medications, especially cephalosporins and other penicillins. Contact your doctor at once if you experience signs of an allergic reaction, such as skin rash, itching, difficulty breathing or swelling of the face and throat.

Antibiotic-associated colitis: This medication, like other antibiotics, may cause a potentially dangerous condition called antibiotic-associated, or pseudomembranous, colitis. Symptoms include severe, watery diarrhea that may be bloody. If you notice these symptoms, stop taking penicillin and contact your doctor as soon as possible.

Birth control: Whether penicillin decreases the effectiveness of birth control pills is controversial. Some doctors recommend adding another method of birth control for the rest of the menstrual cycle when penicillin is taken.

Kidney function: Penicillin is removed from the body by the kidneys. People with impaired kidney function are at risk of increased side effects and may need lower doses of penicillin. People with kidney disease or reduced kidney function should discuss with their doctor how this medication may affect their medical condition, how their medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Overgrowth of organisms: Prolonged treatment with penicillin may allow normal fungus or types of bacteria not killed by the antibiotic to overgrow, causing unwanted infections such as yeast infections.

Pregnancy: Usual doses of penicillin appear to be safe during pregnancy.

Breast-feeding: This medication passes into breast milk. If you are a breast-feeding mother and are taking penicillin, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

What other drugs could interact with this medication?

There may be an interaction between penicillin and any of the following:

  • birth control pills
  • chloramphenicol
  • erythromycin
  • fusidic acid
  • methotrexate
  • mycophenolate
  • probenecid
  • tetracycline antibiotics (e.g., doxycycline, minocycline, tetracycline)
  • typhoid vaccine

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

  • stop taking one of the medications,
  • change one of the medications to another,
  • change how you are taking one or both of the medications, or
  • leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.