What are the lactam drugs

When we have a cold or fever, doctors often prescribe some antibiotics. In fact, many antibiotics, such as penicillin or cephalosporins, belong to the class of beta-lactam drugs. These drugs have been widely used in medical treatment and are very effective with strong bactericidal ability. Beta-lactam drugs include not only some antibiotics, but also many other types of drugs. So, what are the beta-lactam drugs?

β-lactam antibiotics (β-lactams) refer to a large class of antibiotics with a β-lactam ring in their chemical structure, including the most commonly used penicillins and cephalosporins in clinical practice, as well as newly developed cephalomycins, thiomycins, monocyclic β-lactams and other atypical β-lactam antibiotics. This type of antibiotic has the advantages of strong bactericidal activity, low toxicity, wide indications and good clinical efficacy. Changes in the chemical structure of this class of drugs, especially changes in the side chains, have resulted in many antibiotics with different antibacterial spectra and antibacterial effects as well as various clinical pharmacological properties.

Factors Affecting the Antibacterial Effect of β-lactams

The structures of Gram-positive bacteria and Gram-negative bacteria are very different, and the different side chains connected to the parent nucleus can affect the lipophilicity or hydrophilicity of each β-lactam drug. Effective drugs must be able to enter the bacteria and act on target PBPs on the cell membrane. The main factors affecting the antibacterial effect are:

① The ease with which the drug penetrates the cell wall of Gram-positive bacteria or the lipoprotein outer membrane of Gram-negative bacteria (i.e., the first penetration barrier);

② Stability to β-lactamase (the second enzyme hydrolysis barrier);

③ Affinity for antibacterial target PBPs.

Based on these factors, there are roughly six types of effects of β-lactams currently used in clinical practice on Gram-positive and Gram-negative bacteria.

Class I penicillins and oral penicillin V can easily penetrate the mucopeptide layer of the cell wall of Gram-positive bacteria, but they cannot penetrate the glycoprotein phospholipid outer membrane of Gram-negative bacteria. Therefore, they are narrow-spectrum and are only effective against Gram-positive bacteria.

Class II includes ampicillin, carbenicillin, urea penicillins, imipenem and some cephalosporins, which can moderately penetrate the cell wall mucopeptide layer of Gram-positive bacteria and have good permeability to the outer membrane of Gram-negative bacteria, making them broad-spectrum antibacterial drugs.

Class III penicillins are easily inactivated by the extracellular β-lactamase penicillinase of Gram-positive bacteria, and often show obvious resistance to enzyme-producing bacteria.

Class IV includes isoxazole penicillins, first- and second-generation cephalosporins, and imipenem, which are stable to penicillinase and effective against Gram-positive enzyme-producing bacteria. However, they are ineffective against PBPs whose structures are altered by chromosomal mutations, which may reduce or eliminate the affinity between the drug and PBPs.

Class V includes urea penicillins (such as azlocillin and mezlocillin), carbenicillin, and first and second generation cephalosporins. They have antibacterial effects when a small amount of β-lactamase is present in the extracellular space. When a large amount of the enzyme is present, it is destroyed and becomes ineffective.

Class VI includes third-generation cephalosporins, aztreonam, imipenem, etc., which are very stable against β-lactamase and are still effective even in the presence of large amounts of β-lactamase. However, they are ineffective against PBPs that have changed due to chromosomal mutations, and the addition of aminoglycoside antibiotics is still ineffective.