Methicillin-resistant Staphylococcus aureus, or MRSA, is a bacterial infection that can infect open wounds, blisters and skin lesions. Normal infection with the bacteria Staphylococcus aureus, or S. aureus, can be treated with a variety of common antibiotics. However, MRSA is a special species of S. aureus that is resistant to most of the drugs traditionally used to fight the bacteria, according to the National Institute of Allergy and Infectious Diseases. MRSA can be fatal if it reaches the patient's bloodstream. Knowledge of which drugs are ineffective in battling MRSA can help physicians avoid these medications and successfully select an antibiotic that will eradicate the infection.
Penicillins
Penicillins are a subgroup of a family on antibiotics called beta-lactams, according to the Chinese University of Hong Kong. These antibiotics prevent the bacteria from reproducing by interfering with the synthesis of the bacterial cell wall. Without a proper cell wall the organism cannot create progeny. Examples of penicillins include amoxicillin, ampicillin, penicillin and methicillin.
Throughout the 1940s and 1950s, S. aureus gradually developed a resistance to penicillins. Methicillin, a form of penicillin, was at first effective at treating the bacterial infection, but by 1961, S. aureus had become resistant to the drug. This was the birth of MRSA.
Cephalosporins
Cephalosporins are another type of beta-lactam antibiotics that have been found ineffective in battling MRSA. Cephalosporin is normally used to control bacterial infections that have spread throughout the body. This category of medication has been used to cure infections of bacteria that have proven resistant to penicillins such as amoxicillin, according to Drugs.com. In MRSA, however, cephalosporins have proven ineffective. The resistance is probably due to structural changes in the S. aureus bacteria that block the drug from entering the system. Cephalosporins include cefalexin, cefazolin and cefaclor.
Carbapenems
Carbapenems are beta-lactam antibiotics that inhibit cell wall synthesis and are effective in combating bacterial infections, according to SRS Pharmaceuticals. These antibiotics are often combined with other antibiotics to ward off bacterial infection. Carbapenems can be classified into three groups: Group 1, Group 2 and Group 3. Group 1 and 2 have proven ineffective against MRSA. These drugs are inactivated by the bacteria and should not be used in patients suspected of having a MRSA infection. Ertapenem, imipenem, meropenem and doripenem are all examples of group 1 and 2 carbapenems.
Group 3 carbapenems, which only include the experimental agent CS-023, have been found to have an anti-MRSA effect, reports the European Society of Clinical Microbiology and Infectious Diseases. This group has only recently been developed but shows promise in creating more drugs that can be used to treat MRSA.
References
- European Society of Clinical Microbiology and Infectious Diseases: Should All Carbapenems Be Viewed the Same?
- SRS Pharmaceuticals: Carbapenems
- Drugs.com: Cephalosporin
- Chinese University of Hong Kong: Beta-lactams
- National Institute of Allergy and Infectious Diseases: Methicillin-Resistant Staphylococcus Aureus (MRSA)
