Examples

How It Works

Penicillins are antibiotics that kill bacteria.

Why It Is Used

Doctors use penicillins to fight a variety of infections, including pneumococcal pneumonia, meningococcal meningitis, and some strains of Haemophilus influenzae. Penicillins are the antibiotics of choice in fighting uncomplicated infections caused by Streptococcus pneumoniae, the most common cause of pneumonia when the cause is identified.¹

How Well It Works

In general, all antibiotics used have a high cure rate for pneumonia. For people in the hospital, cure rates are 73% to 96%. Outside of the hospital, cure rates are generally above 80%.²

Penicillins kill some types of bacteria that cause pneumonia. These bacteria include Streptococcus pneumoniae, Staphylococcus aureus, and Haemophilus influenzae.

In some cases, bacteria are resistant to penicillins, so other types of antibiotics may be a better choice.

Penicillin may be more effective when it is used with another medicine such as clavulanate.

Penicillin is not effective against Mycoplasma pneumoniae or Chlamydophila pneumoniae, which are common causes of pneumonia in otherwise healthy people.

Side Effects

The main side effects of penicillin are:

• Skin rashes.
• Nausea.
• Discolored or sore tongue.
• Mild diarrhea and upset stomach, especially if you take the medicine on an empty stomach.

People who are allergic to penicillins may have a severe reaction. If they have had such a reaction to penicillins in the past, they should take another kind of antibiotic. Signs of severe allergic reaction include difficulty breathing and a tight throat.

See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

What To Think About

Penicillins cannot always kill bacteria (antibiotic resistance), in part because they are used too much. You can help prevent antibiotic resistance by taking all of your medicine as directed, even if you feel better after a few days. If you stop taking your medicine too soon, bacteria that are not killed in the first few days of treatment can grow stronger and become resistant to the antibiotic.

Complete the new medication information form (PDF)(What is a PDF document?) to help you understand this medication.

Citations

1. Simon HB (2006). Pneumonia and other pulmonary infections. In DC Dale, DD Federman, eds., ACP Medicine, section 7, chap. 20. New York: WebMD.

2. Loeb M (2006). Community acquired pneumonia, search date April 2005. Online version of Clinical Evidence (15): 1–10.