Anti-infective Agents

Anti-infective Agents

Drug Therapy Across the Lifespan

Drug Therapy Across the Lifespan

Drug Therapy Across the Lifespan

Development of Anti-infective Therapy

  • 1920s
    • Paul Ehrlich worked on developing a synthetic chemical effective against infection-causing cells only
    • Scientists discovered penicillin in a mold sample
  • 1935
    • The sulfonamides were introduced

Mechanisms of Action

  • Interfere with biosynthesis of the bacterial cell wall
  • Prevent the cells of the invading organism from using substances essential to their growth and development
  • Interfere with steps involved in protein synthesis
  • Interfere with DNA synthesis
  • Alter the permeability of the cell membrane to allow essential cellular components to leak out

Mechanism of Anti-infective Agents

Mechanism of Anti infective Agents

Mechanism of Anti infective Agents

Anti-infective Activity

  • Anti-infectives vary in their effectiveness against invading organisms
  • Some are selective: they are effective only for a small number of organisms
  • Bactericidal: kill the cell
  • Bacteriostatic: prevent reproduction of the cell

Narrow Spectrum vs Broad Spectrum

  • Narrow spectrum of activity
    • Effective against only a few microorganisms with a very specific metabolic pathway or enzyme
  • Broad spectrum of activity
    • Useful in treating a wide variety of infections

Human Immune Response

  • Goal of anti-infective therapy is reduction of the population of the invading organism
  • Drugs that eliminate all traces of any invading pathogen might be toxic to the host as well
  • Immune response is a complex process involving chemical mediators, leukocytes, lymphocytes, antibodies, and locally released enzymes and chemicals

Problems With Treating Infections in Immunosuppressed Patients

  • Anti-infective drugs cannot totally eliminate the pathogen without causing severe toxicity in the host
  • These patients do not have the immune response in place to deal with even a few invading organisms

Resistance

  • Anti-infectives act on a specific enzyme system or biological process; many microorganisms that do not act on a specific system are not affected by the particular drug
  • This is considered natural or intrinsic resistance to that drug

Acquired Resistance

  • Microorganisms that were once sensitive to the particular drug have begun to develop acquired resistance
  • This results in serious clinical problems

Ways Resistance Develops

  • Producing an enzyme that deactivates the antimicrobial drug
  • Changing cellular permeability to prevent the drug from entering the cell
  • Altering transport systems to exclude the drug from active transport into the cell
  • Altering binding sites on the membranes or ribosomes, which then no longer accept the drug
  • Producing a chemical that acts as an antagonist to the drug

Preventing Resistance

  • Limit the use of antimicrobial agents to the treatment of specific pathogens sensitive to the drug being used
  • Make sure doses are high enough, and the duration of drug therapy long enough
  • Be cautious about the indiscriminate use of anti-infectives

Identification of the Pathogen

  • Identification of the infecting pathogen is done by culture
  • A culture of a tissue sample from the infected area is done
    • A swab of infected tissue is allowed to grow on an agar plate
    • Staining techniques and microscopic examination identify the bacterium
  • Stool can be examined for ova and parasites

Sensitivity of Pathogen

  • Shows which drugs are capable of controlling the particular microorganism
  • Important to be done for microorganisms that have known resistant strains
  • Along with a culture, identifies the pathogen and appropriate drug for treatment

Factors Affecting Prescribing Anti-infective Agents

  • Identification of the correct pathogen
  • Selection of the right drug
    • One that causes the least complications for that particular patient
    • One that is most effective against the pathogen involved

Combination Therapy

  • Use of a smaller dosage of each drug
  • Some drugs are synergistic
  • In infections caused by more than one organism, each pathogen may react to a different anti-infective agent
  • Sometimes, the combined effects of the different drugs delay the emergence of resistant strains

Adverse Reactions to Anti-infective Therapy

  • Kidney damage
  • Gastrointestinal (GI) tract toxicity
  • Neurotoxicity
  • Hypersensitivity reactions
  • Superinfections

Prophylaxis of Anti-infective Agents

  • People traveling to areas where malaria is endemic
  • Patients who are undergoing gastrointestinal or genitourinary surgery
  • Patients with known cardiac valve disease, valve replacements, and other conditions requiring invasive procedures
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