Penicillins are a subclass of antibiotics Overview of Antibiotics Antibiotics are drugs used to treat bacterial infections. They are not effective against viral infections and most other infections. Antibiotics either kill bacteria or stop them from reproducing... read more called beta-lactam antibiotics (antibiotics that have a chemical structure called a beta-lactam ring). Carbapenems Carbapenems Carbapenems are a subclass of antibiotics called beta-lactam antibiotics (antibiotics that have a chemical structure called a beta-lactam ring). Beta-lactam antibiotics also include cephalosporins... read more , cephalosporins Cephalosporins Cephalosporins are a subclass of antibiotics called beta-lactam antibiotics (antibiotics that have a chemical structure called a beta-lactam ring). Beta-lactam antibiotics also include carbapenems... read more , and monobactams Aztreonam Aztreonam is the only antibiotic in an antibiotic class called monobactams, which are a subclass of beta-lactam antibiotics (antibiotics that have a chemical structure called a beta-lactam ring)... read more are also beta-lactam antibiotics.
Penicillins are used to treat infections caused by gram-positive bacteria Staining and Examination Using a Microscope (such as streptococcal infections Streptococcal Infections Streptococcal infections are caused by any one of several species of Streptococcus. These gram-positive, sphere-shaped (coccal) bacteria (see figure How Bacteria Shape Up) cause many... read more ) and some gram-negative bacteria Overview of Gram-Negative Bacteria Bacteria are classified by how they appear under the microscope and by other features. Gram-negative bacteria are classified by the color they turn after a chemical process called Gram staining... read more (such as meningococcal infections Meningococcal Infections Meningococcal infections are caused by the bacteria Neisseria meningitidis (meningococci) and include meningitis and sepsis. Infection is spread by direct contact with nasal and throat... read more ).
Penicillins include the following:
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:
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.
(See also Overview of Antibiotics Overview of Antibiotics Antibiotics are drugs used to treat bacterial infections. They are not effective against viral infections and most other infections. Antibiotics either kill bacteria or stop them from reproducing... read more .)
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 Drug Use During Pregnancy More than 50% of pregnant women take prescription or nonprescription (over-the-counter) drugs or use social drugs (such as tobacco and alcohol) or illicit drugs at some time during pregnancy... read more .)
Use of penicillins during breastfeeding is generally considered acceptable. (See also Drug Use During Breastfeeding Drug Use During Breastfeeding When mothers who are breastfeeding have to take a drug, they wonder whether they should stop breastfeeding. The answer depends on the following: How much of the drug passes into the milk Whether... read more .)