Merck Manual

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Brian J. Werth

, PharmD, University of Washington School of Pharmacy

Last full review/revision Jul 2020| Content last modified Jul 2020
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Penicillins include the following:

  • Amoxicillin

  • Ampicillin

  • Carbenicillin

  • Dicloxacillin

  • Nafcillin

  • Oxacillin

  • Penicillin G

  • Penicillin V

  • 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:

  • Ampicillin plus sulbactam

  • Amoxicillin plus clavulanate

  • Piperacillin plus tazobactam

  • Ticarcillin 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 (when taken by mouth) because amoxicillin is absorbed Drug Absorption Drug absorption is the movement of a drug into the bloodstream after administration. (See also Introduction to Administration and Kinetics of Drugs.) Absorption affects bioavailability—how quickly... read more into the bloodstream better, has fewer gastrointestinal side effects, and can be given less frequently.


Use of Penicillins During Pregnancy and Breastfeeding

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