Beta-Lactam Antibiotics: Penicillins, Cephalosporins & More

Beta-Lactam Antibiotics

Penicillins

Classification of Penicillins

• Narrow-Spectrum Penicillins
  • Natural Penicillins: Penicillin G Sodium, Penicillin G Procaine, Penicillin G Benzathine.
  • Acid-Resistant Penicillins: Penicillin V, Pheneticillin, Propicillin.
• Beta-Lactamase Resistant (Antistaphylococcal) Penicillins
  • Oxacillin, Cloxacillin, Methicillin, Nafcillin.
• Broad-Spectrum Penicillins
  • Antipseudomonal Penicillins:
    • Carboxypenicillins: Carbenicillin, Ticarcillin.
    • Ureidopenicillins: Azlocillin, Mezlocillin, Piperacillin.
  • Aminopenicillins (Beta-Lactamase Sensitive): Amoxicillin, Ampicillin.
• Gram-Negative Beta-Lactamase Resistant Penicillins
  • Temocillin.
• Beta-Lactamase Inhibitors
  • Clavulanic Acid, Sulbactam, Tazobactam.

Key Characteristics of Penicillins

• Structure: Composed of a 6-aminopenicillanic acid core, a variable radical side chain, and a beta-lactam ring. Penicillinases are enzymes capable of breaking this ring, inactivating the antibiotic.
• Mechanism of Action: These are bactericidal antibiotics that inhibit the synthesis of peptidoglycan, a crucial component of the bacterial cell wall. The cell wall is important as it supports osmotic pressure, is involved in cell division, facilitates the selective transport of substances, and contributes to antigenicity.
• Bacterial Resistance: Microorganisms like Staphylococcus aureus can develop resistance by producing beta-lactamases that hydrolyze the beta-lactam ring. This resistance is often transmitted via plasmids. To combat this, penicillins are frequently combined with beta-lactamase inhibitors:
  • Amoxicillin + Clavulanic Acid
  • Ampicillin + Sulbactam
  • Piperacillin + Tazobactam
• Antimicrobial Spectrum: Effective against some Gram-positive bacteria, Gram-negative bacteria, and spirochetes.
• Indications: Used for infections of the ear, nose, and throat (ENT), respiratory system, central nervous system (CNS), bones, soft tissues, and urinary tract, as well as gynecological and sexually transmitted infections.
• Adverse Effects: Hypersensitivity reactions, diarrhea, and elevated transaminases.

Cephalosporins

Cephalosporins are reserve, bactericidal antibiotics available for oral and parenteral administration. They are eliminated by the kidneys, can cross the blood-brain barrier and the placenta, and do not exhibit cross-resistance with penicillins.

Generations of Cephalosporins

• First Generation:
  • Parenteral: Cefazolin, Cephalothin, Cephapirin, Cefacetrile.
  • Oral: Cefalexin, Cefadroxil, Cefaclor, Cephradine.
• Second Generation: Cefuroxime, Cefamandole, Cefoxitin, Cefmetazole, Cefatricine.
• Third Generation: Cefotaxime, Ceftizoxime, Ceftazidime, Cefoperazone, Moxalactam, Cefixime.
• Fourth Generation: Cefepime, Cefpirome.

Key Characteristics of Cephalosporins

• Bacterial Resistance: Resistance can occur through the production of beta-lactamases, particularly against third-generation cephalosporins.
• Antibacterial Spectrum: The spectrum of activity against Gram-negative bacteria increases with each successive generation. Third-generation agents are also effective against Pseudomonas.
• Clinical Uses: Indicated for severe infections caused by organisms like Klebsiella and for surgical prophylaxis.
• Adverse Effects: Tenderness, pain, and phlebitis with intramuscular (IM) and intravenous (IV) administration. Nausea with oral administration. Potential for nephrotoxicity.
• Other Adverse Reactions: Coagulation abnormalities, leukopenia, thrombocytopenia, and anemia.

Other Beta-Lactam Antibiotics

• Aztreonam: An antibiotic used for serious infections caused by Pseudomonas and Enterobacteriaceae that are resistant to other antibiotics.
• Imipenem: A very broad-spectrum antibiotic useful against Gram-positive, Gram-negative, and anaerobic bacteria. It is intended for hospital use and can cause phlebitis, allergic reactions, and superinfections.

Antiseptics and Disinfectants

• Chlorinated Compounds: Elemental chlorine, bleach, chloramine.
• Iodine Compounds: Tincture of iodine, Povidone-iodine (Betadine).
• Oxidizing Agents: Hydrogen peroxide, sodium perborate.
• Alcohols: Ethyl alcohol, isopropyl alcohol.
• Biguanides: Chlorhexidine.
• Cationic Detergents: Benzalkonium, cetylpyridinium.
• Mercurial Derivatives: Mercurochrome, Merbromin.
• Silver Derivatives: Silver nitrate.
• Phenols: Hexachlorophene, hexylresorcinol, parachlorophenol.
• Dyes: Gentian violet.