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Beta-Lactam Antibiotics

Beta-Lactam Antibiotics

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Beta-lactam antibiotics
Beta-lactams inhibit cell wall peptidoglycan crosslinking.
Beta-lactams are D-ala D-ala analogs that competitively bind penicillin-binding proteins, aka, transpetidases.
Acquired resistance to beta-lactams is common. – Is often due to bacterial production of beta-lactamases, such as penicillinase.
Beta-lactamase inhibitors can administered with some antibiotics to provide protection from beta-lactamase. Examples include clavulanic acid, sulbactam, and tazobactam.
Beta-Lactams
Penicillin G and Penicillin V Penicillin G is administered intravenously or intramuscularly, and Penicillin V is an oral medication.
Most common uses Gram-positive infections. Also effective against Neisseria meningitidis and Treponema pallidum.
Bacterial resistance Penicillinase cleaves the beta-lactam ring of penicillins.
Adverse effects Hypersensitivity reactions, which are IgE mediated. Hemolytic anemia is also possible (indicated by a positive direct coombs test).
Amoxicillin and Ampicillin Broad-spectrum penicillins. These antibiotics are referred to as aminopenicillins.
Most common uses Gram-positive bacteria, including Enterococci. Key Gram-negative bacteria, including Haemophilus influenzae, Helicobacter pylori, and enteric infections caused by Listeria monocytogenes, Salmonella, and Shigella.
Bacterial resistance Susceptible to penicillinase.
Adverse effects Hypersensitivity reactions; increased risk of pseudomembranous colitis Oxacillin, Nafcillin, Dicloxacillin, and Methicillin Narrow-spectrum penicillins.
Most common uses Staphylococcus aureus infections. NOT effective against MRSA (Methicillin-Resistant Staphylococcus aureus).
Bacterial resistance These penicillins are resistant to penicillinase.
Important Note: Methicillin-Resistant Staphylococcus aureus is resistant to all penicillins due to its mutated transpeptidase binding site. This is an example of bacterial resistance due to modification of a target binding site.
Adverse effects Hypersensitivity reactions.
In the kidney, T-cell mediated hypersensitivity reactions can lead to acute interstitial nephritis. Such reactions can occur with several antibiotic classes, but methicillin is thought to increase the risk.
Piperacillin and ticarcillin Sometimes referred to as "extended spectrum" or "antipseudomonal penicilins."
Most common uses Gram-negative rods; Anaerobes, including Pseudomonas.
Bacterial resistance They are susceptible to beta-lactamases.
Adverse effects Hypersensitivity reactions.
Carbapenems: Imipenem, Meropenem, Ertapenem, and Doripenem
Most common uses Gram-positive cocci Gram-negative rods Anaerobes, including Pseudomonas
Important exceptions: Carbapenems are not effective against Enterococcus faecium or MRSA. Ertapenem is not effective against Pseudomonas.
Bacterial resistance Carbapenemase is a beta-lactamase of growing concern.
Adverse effects Imipenem should be administered with cilastatin to avoid inactivation within the renal tubules.
Watch for Hypersensitivity reactions in patients with penicillin allergies.
Seizures
Gastrointestinal upset are also associated with carbapenems; administer the antibiotics slowly to avoid this.
Monobactram: Aztreonan Narrow-spectrum antibiotic
Most common uses Aerobic Gram-negative rods.
No activity against Gram-positive or anaerobe bacteria/ Synergistic with aminoglycosides (also used in Gram-negative infections), and, it is a is a useful option for patients who are allergic to penicillin because cross-reaction is rare.
Bacterial resistance Less susceptible to beta-lactamase than many other beta-lactams.
Adverse effects Rare.
Betal-Lactams: Cephalosporins
Bacterial Resistance
Beta-lactamase production and/or changes in transpeptidases necessary for peptidoglycan cross-linking (protein-binding proteins).
Adverse Effects – Hypersensitivity reactions – Drug-induced immune hemolytic anemia – A disulfiram-like reaction when combined with alcohol consumption – Hypo-prothrombinemia due to vitamin K deficiency – Pseudomembranous colitis
The potential for vitamin K deficiency and pseudomembranous colitis are the result of broad-spectrum antibiotics that kill the healthy microflora of the gastrointestinal system.
1st Generation: Cephalothin, Cefazolin, and Cephalexin
Most common uses: Gram-positive cocci, specific Gram-negative bacteria, including Proteus mirabilis, Escherichia coli, and Klebisella pneumoniae.
2nd Generation: Cefaclor, Cefoxitin, and Cefuroxime
Expanded-spectrum
Most common uses: Improved activity against key Gram-negative species, including Haemophilus influenzae, Enterobacter, Citrobacter, and Serratia; some anaerobes, such as Bacteroides fragilis.
Compared to the first generation cephalospoprins, the second generation formulations are less effective against Staphylococci.
3rd Generation: Cefotaxime, Ceftriaxone, and Ceftazidime
Most common uses: – Broad spectrum coverage of most Gram-negative bacteria. – Ceftazidime has antipseudomonal activity. – Ceftriaxone and cefotaxime are used to treat Meningitis. – Ceftriaxone is used to treat community-acquired pneumonia, HACEK and Streptococcal endocarditis, Lyme disease, and gonorrhea. – third generation cephalosporins are less effective against Staphylococci.
4th Generation: Cefepime
Most common uses: Extended-spectrum coverage of Gram-negative bacteria; Improved activity against Gram-positive bacteria and Pseudomonas.
5th Generation: Ceftaroline
Most common uses: Broad-spectrum coverage of Gram-positive and Gram-negative bacteria Including MRSA.
NOT effective against Pseudomonas.

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