Antimicrobials

Antimicrobials refer to substances or agents that can inhibit the growth or destroy microorganisms, including bacteria, viruses, fungi, and parasites. These agents are crucial in preventing, controlling, and treating infectious diseases in humans, animals, and plants.

Different classes of antimicrobial agents are designed to target specific types of microorganisms or interfere with their growth and reproduction.

Categories of antimicrobials

1. Antibiotics: Substances derived from living organisms or synthesized in the laboratory specifically target bacteria. Antibiotics can kill bacteria (bactericidal) or inhibit their growth (bacteriostatic).

Bactericidal – kill bacteria.

Bacteriostatic – inhibit bacterial growth and replication.

2. Antivirals: These agents are used to treat viral infections by interfering with various stages of the viral life cycle, such as attachment, entry, replication, or release. Unlike antibiotics, antivirals do not destroy viruses but prevent their propagation.

3. Antifungals: Antifungals inhibit the growth of or kill fungi, which are responsible for superficial infections like dermatophytosis or deep/systemic infections like aspergillosis or candidiasis.

4. Antiparasitic Agents: Medications designed to combat parasitic infections caused by protozoa or helminths. These agents are crucial in treating diseases like malaria and certain worm infestations.

5. Antiseptics and Disinfectants: Chemical substances applied to living tissues (antiseptics) or inanimate objects and surfaces (disinfectants) to eliminate or reduce the number of microorganisms.

The use of antimicrobials has significantly contributed to the control of infectious diseases and the improvement of public health. However, the emergence of antimicrobial resistance is a growing concern, emphasizing the importance of responsible and judicious use of these agents to preserve their efficacy.

Classification of Antimicrobials

Antimicrobials are classified into several categories based on their target microorganisms, mechanisms of action, and specific characteristics. The primary classes of antimicrobials include:

1. Antibiotics:

Penicillins: e.g., Penicillin G, Amoxicillin – inhibit bacterial cell wall synthesis.

Cephalosporins: e.g., Cephalexin, Ceftriaxone – β-lactam antibiotics with broader spectrum.

Macrolides: e.g., Erythromycin, Azithromycin – inhibit bacterial protein synthesis.

Tetracyclines: e.g., Tetracycline, Doxycycline – broad-spectrum protein synthesis inhibitors.

Aminoglycosides: e.g., Gentamicin, Tobramycin – bactericidal agents inhibiting 30S ribosomal subunit.

Fluoroquinolones: e.g., Ciprofloxacin, Levofloxacin – inhibit DNA gyrase and topoisomerase IV.

2. Antivirals:

NRTIs (Nucleoside/Nucleotide Reverse Transcriptase Inhibitors): e.g., Zidovudine, Tenofovir – inhibit HIV reverse transcription.

Protease Inhibitors (PIs): e.g., Ritonavir, Atazanavir – prevent viral maturation.

Neuraminidase Inhibitors: e.g., Oseltamivir, Zanamivir – prevent influenza virus release.

Fusion Inhibitors: e.g., Enfuvirtide – inhibit HIV entry into host cells.

Integrase Inhibitors: e.g., Raltegravir, Dolutegravir – inhibit integration of viral DNA into host genome.

3. Antifungals:

Polyenes: e.g., Amphotericin B, Nystatin – bind to ergosterol in fungal membranes.

Azoles: e.g., Fluconazole, Ketoconazole – inhibit ergosterol synthesis.

Echinocandins: e.g., Caspofungin, Micafungin – inhibit β-glucan synthesis in fungal cell walls.

Allylamines: e.g., Terbinafine – inhibit squalene epoxidase in ergosterol biosynthesis.

4. Antiparasitic Agents:

Antimalarials: e.g., Chloroquine, Artemisinin-based Combination Therapies (ACTs) – interfere with heme detoxification or mitochondrial function in Plasmodium species.

Anthelmintics: e.g., Albendazole, Mebendazole – disrupt glucose uptake or microtubule formation in worms.

Antiprotozoals: e.g., Metronidazole, Quinine – damage DNA or interfere with protozoal metabolism.

5. Antiseptics and Disinfectants:

Alcohols: e.g., Ethanol, Isopropyl alcohol – denature proteins and dissolve lipids.

Quaternary Ammonium Compounds: e.g., Benzalkonium chloride – disrupt membranes.

Halogens: e.g., Iodine, Chlorine compounds – oxidize cellular components.

Chlorhexidine: Used as a skin antiseptic and in surgical scrubs.

6. Others:

Sulfonamides and Trimethoprim: e.g., Sulfamethoxazole-Trimethoprim – inhibit folic acid synthesis.

Nitrofurans: e.g., Nitrofurantoin – disrupt bacterial ribosomes and DNA.

Glycopeptides: e.g., Vancomycin, Teicoplanin – inhibit peptidoglycan synthesis in Gram-positive bacteria

Clinical Significance and Challenges

The therapeutic success of antimicrobials in the 20th and 21st centuries has significantly reduced the global burden of infectious diseases. However, irrational use, such as overprescription, incomplete courses, and misuse in agriculture, has led to the emergence of resistant strains like MRSA, MDR-TB, and ESBL-producing bacteria.

Antimicrobial Stewardship

Programs focusing on the judicious selection, dosing, and duration of antimicrobial therapy are vital to:

• Delay resistance.
• Preserve drug efficacy.
• Improve patient outcomes.

It’s important to note that individual agents may have variations in their spectrum of activity, mechanisms of action, and clinical uses within each class. Additionally, the classification may evolve as new antimicrobial agents are developed and introduced into clinical practice.