Essential Antimicrobial and Antiviral Pharmacotherapy

Posted on Mar 21, 2026 in Microbiology

Beta-Lactam Antibiotics

Beta-lactam antibiotics are a broad class of bactericidal agents containing a characteristic four-sided ring, including penicillins, cephalosporins, carbapenems, and monobactams. They treat infections by binding to penicillin-binding proteins (PBPs), inhibiting cell wall synthesis, and causing bacterial lysis. Key challenges include bacterial resistance via beta-lactamase enzymes and hypersensitivity reactions.

Mechanism of Action

These antibiotics inhibit the final step of bacterial peptidoglycan synthesis (cell wall formation) by binding to and acylating transpeptidases (PBPs). This causes weakened cell walls and eventual cell lysis.

Main Classes

  • Penicillins: (e.g., Amoxicillin, Penicillin G) Used for various bacterial infections.
  • Cephalosporins: (e.g., Ceftin/Cefuroxime axetil, Vantin/Cefpodoxime proxetil) Classified by five generations.
  • Carbapenems: (e.g., Meropenem, Imipenem) Known for broad-spectrum activity, often used for severe, resistant infections.
  • Monobactams: (e.g., Aztreonam) Often used for aerobic gram-negative bacteria, especially in patients with penicillin allergies.

Resistance and Side Effects

Resistance Mechanism: Bacteria often develop resistance by producing beta-lactamase enzymes, which break open the beta-lactam ring and inactivate the drug. Counter-measures: Combination drugs, such as Augmentin (amoxicillin-clavulanate), are used to combat beta-lactamase-producing bacteria. Side Effects: The most common adverse reaction is hypersensitivity, with beta-lactams causing 42.6% of all drug-induced anaphylaxis.

Penicillin Overview

Penicillin is a group of beta-lactam antibiotics derived from Penicillium fungi, discovered by Alexander Fleming in 1928. It treats bacterial infections (e.g., strep throat, syphilis, meningitis) by inhibiting cell wall synthesis, causing bacterial death.

Key Characteristics

  • Mechanism of Action: Kills bacteria by preventing the construction of peptidoglycan, which is essential for cell wall structural integrity.
  • Spectrum: Primarily effective against Gram-positive bacteria.
  • Common Side Effects: Nausea, diarrhea, and allergic reactions (hives, rash, anaphylaxis).
  • Resistance: Some bacteria produce penicillinase, an enzyme that breaks down the antibiotic.
  • Common Types: Penicillin V, Penicillin G, Amoxicillin, and Ampicillin.

Tuberculosis (TB) Treatment

Tuberculosis is a chronic granulomatous disease and a major health problem. It is an infectious disease usually caused by Mycobacterium tuberculosis (MTB) bacteria, primarily affecting the lungs. Most infections are latent, but 10% progress to active disease, characterized by chronic cough with blood-containing mucus, fever, night sweats, and weight loss.

Classification of Antitubercular Drugs

First-Line Drugs

  1. Isoniazid (H)
  2. Rifampin (R)
  3. Pyrazinamide (Z)
  4. Ethambutol (E)
  5. Streptomycin (S)

Second-Line Drugs

  • Ethionamide (Eto), Prothionamide (Pto), Cycloserine (Cs), Terizidone (Trd), Para-aminosalicylic acid (PAS), Rifabutin, Thiacetazone (Thz)
  • Fluoroquinolones: Ofloxacin (Ofx), Levofloxacin (Lvx/Lfx), Moxifloxacin (Mfx), Ciprofloxacin (Cfx)
  • Injectable drugs: Kanamycin (Km), Amikacin (Am), Capreomycin (Cm)

Mechanism of Action

Antitubercular drugs target Mycobacterium tuberculosis through the inhibition of cell wall synthesis, protein synthesis, or nucleic acid metabolism:

  • Isoniazid (INH): Inhibits mycolic acid synthesis by targeting the InhA enzyme.
  • Rifampicin (RIF): Inhibits bacterial DNA-dependent RNA polymerase.
  • Pyrazinamide (PZA): Disrupts membrane energy metabolism.
  • Ethambutol (EMB): Inhibits arabinosyltransferase, preventing cell wall polymerization.

Antiviral Medications

Antiviral medications are prescription drugs that help the body fight viral infections by reducing symptoms, shortening illness duration, and lowering viral load. They work by blocking virus entry into cells, inhibiting replication, or boosting the immune system.

Classification

  • Anti-herpes virus drugs: Idoxuridine, Acyclovir, Valacyclovir, Famciclovir, Ganciclovir, Valganciclovir, Cidofovir, Foscarnet.
  • Anti-influenza virus drugs: Amantadine, Rimantadine, Oseltamivir, Zanamivir.
  • Anti-hepatitis/Nonselective: Lamivudine, Adefovir dipivoxil, Tenofovir (for Hep B); Ribavirin, Interferon a (for Hep C).

Antifungal Medications

Antifungal medications are agents that kill fungi or inhibit their growth. Key classes include Azoles, Polyenes, and Echinocandins, available as topicals, oral pills, or IV injections.

Clinical Classification

1. Systemic Agents

  • Antibiotics: Amphotericin B, Griseofulvin
  • Antimetabolites: Flucytosine (5-FC)
  • Azoles: Ketoconazole, Fluconazole, Itraconazole, Voriconazole
  • Allylamine: Terbinafine
  • Echinocandins: Caspofungin, Micafungin, Anidulafungin

2. Topical Agents

  • Polyene Antibiotics: Nystatin, Hamycin, Natamycin
  • Azoles: Clotrimazole, Miconazole, Econazole
  • Miscellaneous: Tolnaftate, Undecylenic acid, Benzoic acid