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Penicillins ˌpen-ə-ˈsil-ən

By Hans P. Schlecht, MD, MSc, Assistant Professor of Medicine, Department of Medicine, Division of Infectious Diseases & HIV Medicine, Drexel University College of Medicine ; Christopher Bruno, MD, Assistant Professor of Medicine, Division of infectious Diseases & HIV Medicine, Drexel University College of Medicine

Penicillins are a subclass of antibiotics called beta-lactam antibiotics (antibiotics that have a chemical structure called a beta-lactam ring). Carbapenems, cephalosporins, and monobactams are also beta-lactam antibiotics.

Penicillins are used to treat infections caused by gram-positive bacteria (such as streptococcal infections) and some gram-negative bacteria (such as meningococcal infections).

Penicillins include the following:

  • Amoxicillin

  • Ampicillin

  • Carbenicillin

  • Dicloxacillin

  • Nafcillin

  • Oxacillin

  • Penicillin G

  • Penicillin V

  • Piperacillin

  • Ticarcillin

Some bacteria have an outer covering (cell wall) that protects them. Like the other beta-lactam antibiotics, penicillins work by preventing bacteria from forming this cell wall, resulting in death of the bacteria.

Some bacteria produce enzymes that can inactivate beta-lactam antibiotics. For infections caused by these bacteria, penicillins are given with a drug that can inhibit these enzymes, such as clavulanate or sulbactam. Common combinations include the following:

  • Ampicillin plus sulbactam

  • Amoxicillin plus clavulanate

Some penicillins can be given by mouth (for example, amoxicillin and penicillin V) or by injection (for example, piperacillin). Others (such as ampicillin) can be given either way.

Food does not interfere with the absorption of amoxicillin, but penicillin G should be taken 1 hour before or 2 hours after a meal. Amoxicillin tends to be used more often than ampicillin (taken by mouth) because amoxicillin is absorbed better, has fewer gastrointestinal side effects, and can be given less frequently.

Penicillins

Drug

Common Uses

Some Side Effects

Amoxicillin

Ampicillin

Carbenicillin

Dicloxacillin

Nafcillin

Oxacillin

Penicillin G

Penicillin V

Piperacillin

Ticarcillin

Wide range of infections, including streptococcal infections, syphilis, and Lyme disease

Nausea, vomiting, and diarrhea*

Brain and kidney damage (rare)

*Almost any antibiotic can cause Clostridium difficile–induced diarrhea and inflammation of the colon (colitis), but clindamycin, penicillins, cephalosporins, and fluoroquinolones are the most common causes.

Use of Penicillins During Pregnancy and Breastfeeding

Penicillins are among the safest antibiotics to use during pregnancy. However, they are used only when the benefits of treatment outweigh the risks.

Use of penicillins during breastfeeding is generally considered acceptable.

Resources In This Article

Drugs Mentioned In This Article

  • Generic Name
    Select Brand Names
  • AMOXIL
  • No US brand name
  • BACTOCILL IN PLASTIC CONTAINER
  • CLEOCIN
  • NALLPEN IN PLASTIC CONTAINER