ByBrian J. Werth, PharmD, University of Washington School of Pharmacy
Reviewed/Revised Jun 2022 | Modified Sep 2022

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:

  • Carbenicillin

  • Piperacillin

  • Ticarcillin

Most 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:

  • Piperacillin/tazobactam

  • Ticarcillin plus clavulanate

absorbed into the bloodstream better, has fewer gastrointestinal side effects, and can be given less frequently.


(See also Overview of Antibiotics.)

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. (See also Drug Use During Pregnancy.)

Use of penicillins during breastfeeding is generally considered acceptable. (See also Drug Use During Breastfeeding.)

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