Antibiotics: Types and Mechanisms

• Antibiotics are medicines that fight bacterial infections in humans and animals.
• They work by killing the bacteria or making it difficult for the bacteria to grow and multiply.
• Antibiotics do not work against viral infections, such as cold, flu, and most coughs.

Types of Antibiotics

• Antibiotics are classified based on their mechanism of action:
  • Inhibition of cell wall synthesis: Prevents bacteria from building cell walls.
  • Inhibition of protein synthesis: Interferes with bacterial protein production.
  • Inhibition of nucleic acid synthesis: Disrupts DNA/RNA production.
  • Inhibition of metabolic pathways: Blocks folate production required for bacterial growth.
  • Disruption of cell membrane: Alters the cell membrane permeability.

Common Antibiotic Classes and Examples

• Penicillins:
  • Including penicillin, amoxicillin, and methicillin.
  • Act by inhibiting bacterial cell wall synthesis.
  • Effective against a wide range of bacteria.
• Cephalosporins:
  • Including cefalexin and ceftriaxone.
  • Also inhibit cell wall synthesis.
  • Used for various infections, including pneumonia and skin infections.
• Macrolides:
  • Including erythromycin, azithromycin, and clarithromycin.
  • Inhibit bacterial protein synthesis.
  • Often prescribed for respiratory and skin infections.
• Tetracyclines:
  • Including tetracycline and doxycycline.
  • Inhibit bacterial protein synthesis.
  • Used to treat acne, respiratory infections, and certain STIs.
• Fluoroquinolones:
  • Including ciprofloxacin and levofloxacin.
  • Inhibit bacterial DNA replication.
  • Effective against a broad spectrum of bacteria.
• Aminoglycosides:
  • Including gentamicin and tobramycin.
  • Inhibit bacterial protein synthesis by binding to the 30S ribosomal subunit.
  • Often used for severe infections.
• Sulfonamides:
  • Including sulfamethoxazole.
  • Inhibit folate synthesis.
  • Commonly used to treat urinary tract infections and skin infections.
• Glycopeptides:
  • Including vancomycin.
  • Inhibit cell wall synthesis.
  • Used to treat severe infections caused by Gram-positive bacteria, especially MRSA.
• Carbapenems:
  • Including imipenem and meropenem.
  • Inhibit cell wall synthesis.
  • Reserved for severe or high-risk infections, due to their broad spectrum of activity and potential for resistance development.

Administration of Antibiotics

• Antibiotics can be administered through various routes:
  • Oral: Taken by mouth, usually in the form of tablets, capsules, or liquids.
  • Intravenous (IV): Injected directly into a vein.
  • Intramuscular (IM): Injected into a muscle.
  • Topical: Applied to the skin in the form of creams, ointments, or lotions.
• The route of administration depends on the type and severity of the infection, as well as the patient's condition.

Antibiotic Resistance

• Antibiotic resistance occurs when bacteria evolve to withstand the effects of antibiotics:
  • Overuse and misuse of antibiotics are major drivers of antibiotic resistance.
  • Resistant bacteria can spread to humans and animals, making infections harder to treat.
  • Antibiotic resistance is a global health threat.
• Mechanisms of Antibiotic Resistance:
  • Enzymatic inactivation: Bacteria produce enzymes that break down or modify the antibiotic.
  • Target modification: Bacteria alter the structure of the antibiotic's target site, reducing its binding affinity.
  • Reduced permeability: Bacteria decrease the uptake of antibiotics or increase their efflux (pumping out).
  • Bypass pathways: Bacteria develop alternative metabolic pathways to circumvent the antibiotic's effects.
• Strategies to Combat Antibiotic Resistance:
  • Antibiotic stewardship: Implementing policies and practices to optimize antibiotic use.
  • Infection prevention and control: Reducing the spread of resistant bacteria through hygiene and isolation measures.
  • Development of new antibiotics: Investing in research and development to discover novel antibacterial agents.
  • Diagnostic testing: Improving the accuracy and speed of bacterial identification and susceptibility testing.
  • Public education: Educating healthcare professionals and the public about antibiotic resistance and responsible antibiotic use.

Side Effects of Antibiotics

• Common side effects of antibiotics include:
  • Nausea, vomiting, and diarrhea: Due to disruption of the gut microbiota.
  • Allergic reactions: Ranging from mild skin rashes to severe anaphylaxis.
  • Yeast infections: Overgrowth of yeast in the mouth, throat, or vagina.
  • Antibiotic-associated diarrhea: Including Clostridium difficile infection.
  • Photosensitivity: Increased sensitivity to sunlight.
  • Drug interactions: Interference with other medications.
• Uncommon but serious side effects include:
  • Kidney damage: Some antibiotics can be toxic to the kidneys.
  • Liver damage: Some antibiotics can cause liver inflammation or dysfunction.
  • Hearing loss: Some antibiotics can damage the nerves in the inner ear.
  • Blood disorders: Some antibiotics can affect the production of blood cells.
  • Tendon rupture: Fluoroquinolone antibiotics have been associated with an increased risk of tendon rupture.

Considerations for Antibiotic Use

• Antibiotics should only be used when they are truly necessary.
• It's important to take antibiotics exactly as prescribed.
• Complete the full course of antibiotics, even if symptoms improve.
• Do not share antibiotics with others or save them for later use.
• Inform healthcare providers about any allergies or other medications.
• Probiotics:
  • Probiotics may help reduce the risk of antibiotic-associated diarrhea.
  • Need to be taken separately from the antibiotic dose.

Antibiotics in Animals

• Antibiotics are also used in animals for treating and preventing infections.
• However, the use of antibiotics in animals can contribute to antibiotic resistance.
• Responsible use of antibiotics in animals is important to protect human health.