Antibiotic and Antiviral Drug Classes
Beta-lactam antibiotics share common chemical features. They include penicillins, cephalosporins, and some newer similar medications. They interfere with bacterial cell walls.
Penicillins. Penicillin was the first antibiotic. There are many forms of this still-important drug:
- Natural penicillins include penicillin G (for intravenous use) and V (for oral use).
- Penicillin derivatives called aminopenicillins, particularly amoxicillin (Amoxil, Polymox, Trimox, Wymox, or any generic formulation), are now the most common penicillins used. Amoxicillin is inexpensive and, at one time, was highly effective against S. pneumoniae. Unfortunately, bacterial resistance to amoxicillin has increased significantly, both among S. pneumoniae and H. influenzae. Ampicillin is similar and is an alternative to amoxicillin, but requires more doses and has more severe gastrointestinal side effects.
- Amoxicillin-clavulanate (Augmentin) is a type of penicillin that works against a wide variety of bacteria. An extended-release form has been approved for treating adults with community-acquired pneumonia caused by bacterial strains that have become partially resistant to penicillin.
- Antistaphylococcal penicillins were developed to treat Staphylococcus aureus. The standard drug was methicillin, but it is no longer used routinely, due to very high rates of resistance in hospital-acquired pneumonias. Resistance in community-acquired Staphylococcus aureus is also increasing. Alternatives include vancomycin and linezolid. There are also other options for this type of bacteria.
- Penicillins used against Pseudomonas aeruginosa include ticarcillin and piperacillin. Piperacillin is more effective than ticarcillin.
Many people have a history of an allergic reaction to penicillin, but research suggests that the allergy may not occur again in a significant number of adults. Skin tests are available to help determine if those with a history of penicillin allergies could use these important antibiotics.
Cephalosporins. Most of these antibiotics are not very effective against bacteria that have developed resistance to penicillin. They are classed according to their generation:
- First generation includes cephalexin (Keflex), cefadroxil (Duricef, Ultracef), and cephradine (Velosef).
- Second generation includes cefaclor (Ceclor), cefuroxime (Ceftin), cefprozil (Cefzil), and loracarbef (Lorabid).
- Third generation includes cefpodoxime (Vantin), cefdinir (Omnicef) cefditoren (Sprectracef), cefixime (Suprax), and ceftibuten (Cedex). Ceftriaxone (Rocephin) is an injected cephalosporin. These are effective against a wide range of Gram-negative bacteria.
Other Beta-Lactam Agents. Carbapenems include meropenem (Merrem), biapenem, faropenem, ertapenem (Invanz) and combinations [imipenem/cilastatin [Primaxin)]. These drugs are used to treat a wide variety of bacteria. They are now used for serious hospital-acquired infections and for bacteria that have become resistant to other beta-lactams. Imipenem has serious side effects when used alone, so it is given in combination with cilastatin to offset these adverse effects. The newer drugs are less toxic, although they may not be as effective.
Sanfetrinem, a new beta-lactam antibiotic known as a trinem, is proving to be effective against S. pneumoniae, H. influenzae, and M. catarrhalis.
Ceftobiprole is an investigational beta-lactam for methicillin-resistant Staphylococcus aureus (MRSA), penicillin-resistant streptococci, and other Gram-negative bacteria. Other anti-MRSA beta-lactams in development include:
Review Date: 04/13/2010
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.