Chemotherapeutic Agents and Their Development
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Questions and Answers

What is one of the main functions of antifungal drugs?

  • To increase cell permeability
  • To bind to sterols in fungal membranes (correct)
  • To promote the development of drug-resistant fungi
  • To enhance fungal growth

    • What can contribute to the development of superinfection?

  • Destruction of drug-sensitive strains by antibiotics (correct)
  • Administration of two or more drugs simultaneously
  • Reduction of the body's detoxification system
  • Use of high concentrations of antifungal drugs

    • What approach is suggested to prevent the emergence of drug resistance?

  • Administer drugs at low doses
  • Use antibiotics for all infections
  • Reduce drug concentrations
  • Limit the use of drugs to necessary cases (correct)

    • Which type of drug is aimed specifically at inhibiting HIV entry into cells?

    <p>Fusion inhibitors</p> Signup and view all the answers

    Which of the following viruses is NOT specifically targeted by broad-spectrum anti-DNA virus drugs?

    <p>Rhinoviruses</p> Signup and view all the answers

    What is the primary reason for the limited number of antiviral drugs available?

    <p>Difficulty in targeting viral replication</p> Signup and view all the answers

    Which class of anti-HIV drugs inhibits enzymes involved in DNA and RNA synthesis?

    <p>Reverse transcriptase inhibitors</p> Signup and view all the answers

    What common outcome results from treatment with certain antibiotics leading to the survival of Clostridium difficile?

    <p>Pseudomembranous enterocolitis</p> Signup and view all the answers

    What is meant by selective toxicity in the context of chemotherapeutic agents?

    <p>The ability of a drug to kill pathogens while causing minimal harm to the host</p> Signup and view all the answers

    Which agent was discovered as the first antibiotic?

    <p>Penicillin</p> Signup and view all the answers

    What does the term Minimum Inhibitory Concentration (MIC) refer to?

    <p>The lowest concentration of a drug that inhibits the growth of a pathogen</p> Signup and view all the answers

    Which of the following mechanisms of action is NOT utilized by penicillins?

    <p>Inhibition of protein synthesis</p> Signup and view all the answers

    Which of the following describes the therapeutic index?

    <p>The ratio of the therapeutic dose to the toxic dose</p> Signup and view all the answers

    What is the primary purpose of the Kirby-Bauer method?

    <p>To measure the effectiveness of an antibiotic against pathogens</p> Signup and view all the answers

    Which statement about sulfonamides is TRUE?

    <p>They are competitive inhibitors of folic acid synthesis.</p> Signup and view all the answers

    What aspect of drug resistance can occur through R plasmids?

    <p>Development of alternative pathways</p> Signup and view all the answers

    Which of the following drugs is used to treat antibiotic-resistant infections?

    <p>Vancomycin</p> Signup and view all the answers

    What does the term 'zone of inhibition' refer to in antimicrobial sensitivity testing?

    <p>The area where bacteria cannot grow due to antibiotic presence</p> Signup and view all the answers

    What is a significant challenge in using antifungal agents?

    <p>Fungal cells share similarities with human cells.</p> Signup and view all the answers

    What is the main action of antibiotics that inhibit nucleic acid synthesis?

    <p>Block DNA replication and transcription</p> Signup and view all the answers

    What factors contribute to the effectiveness of an antimicrobial drug?

    <p>Administration route and pathogen susceptibility</p> Signup and view all the answers

    Which of the following statements about chloramphenicol is correct?

    <p>It is a broad-spectrum antibiotic.</p> Signup and view all the answers

    What is the primary action of most antifungal drugs on fungal membranes?

    <p>Disrupt membrane permeability</p> Signup and view all the answers

    What is a common consequence of administering antibiotics in the treatment of bacterial infections?

    <p>Development of superinfection</p> Signup and view all the answers

    Which of the following is NOT a suggested method for preventing the emergence of drug resistance?

    <p>Administer drugs in lower concentrations</p> Signup and view all the answers

    What is one of the main challenges in developing antiviral drugs?

    <p>Difficulty in specifically targeting viral replication</p> Signup and view all the answers

    Which type of inhibitors prevent the entry of HIV into cells?

    <p>Fusion inhibitors</p> Signup and view all the answers

    What role do reverse transcriptase (RT) inhibitors play in anti-HIV treatment?

    <p>They inhibit the synthesis of RNA from DNA</p> Signup and view all the answers

    Which of the following classes of antiviral drugs specifically inhibits enzymes needed for DNA replication in herpes viruses?

    <p>DNA polymerase inhibitors</p> Signup and view all the answers

    Which approach is considered most effective in treating HIV while curtailing the risk of drug resistance?

    <p>Drug cocktails combining multiple medications</p> Signup and view all the answers

    What does the term 'therapeutic index' represent?

    <p>The ratio of toxic dose to therapeutic dose</p> Signup and view all the answers

    Which mechanism is NOT commonly used by antibiotics to inhibit bacterial growth?

    <p>Inhibition of carbohydrate metabolism</p> Signup and view all the answers

    Which of the following factors does NOT influence the effectiveness of antimicrobial drugs?

    <p>Dosage schedule of the drug</p> Signup and view all the answers

    How is the minimal lethal concentration (MLC) determined?

    <p>By subculturing into drug-free medium from tubes showing no growth</p> Signup and view all the answers

    What is a common outcome of drug resistance in pathogens?

    <p>Inhibition of drug penetration into pathogens</p> Signup and view all the answers

    Penicillin's mode of action primarily involves what mechanism?

    <p>Blocking transpeptidation in peptidoglycan</p> Signup and view all the answers

    Which of the following is true about cephalosporins?

    <p>They can be used by most patients allergic to penicillin</p> Signup and view all the answers

    What type of drugs are sulfonamides considered?

    <p>Static agents that inhibit growth</p> Signup and view all the answers

    What is the primary concern regarding the use of vancomycin?

    <p>The rise of resistance against this 'drug of last resort'</p> Signup and view all the answers

    Which test is characterized by placing drug-impregnated disks on agar plates?

    <p>Kirby-Bauer method</p> Signup and view all the answers

    What characteristic makes chloramphenicol potentially dangerous?

    <p>It can cause serious side effects in humans</p> Signup and view all the answers

    What defines broad-spectrum antimicrobial drugs?

    <p>Effective against a wide range of different pathogens</p> Signup and view all the answers

    The E test is used to determine which of the following?

    <p>Minimum inhibitory concentration</p> Signup and view all the answers

    Which discovery is attributed to Selman Waksman?

    <p>Streptomycin</p> Signup and view all the answers

    Study Notes

    Chemotherapeutic Agents

    • Chemical agents used to treat disease
    • Destroy pathogenic microbes or inhibit their growth in the host
    • Most are antibiotics
    • Are microbial products or their derivatives that kill susceptible microbes or inhibit their growth

    The Development of Chemotherapy

    • Paul Ehrlich (1904) developed the concept of selective toxicity
    • Identified dyes that effectively treated African sleeping sickness
    • Sahachiro Hato (1910), working with Ehrlich, identified arsenic compounds that effectively treated syphilis
    • Gerhard Domagk, and Jacques and Therese Trefouel (1935) discovered sulfonamides and sulfa drugs

    Penicillin

    • First discovered by Ernest Duchesne (1896), but the discovery was lost
    • Accidentally discovered by Alexander Fleming (1928)
    • Observed penicillin activity on contaminated plates
    • Did not think it could be developed further
    • Effectiveness demonstrated by Florey, Chain, and Heatley (1939)

    Later Discoveries

    • Streptomycin, an antibiotic active against tuberculosis, was discovered by Selman Waksman (1944)
    • Nobel Prize awarded to Waksman in 1952 for this discovery
    • By 1953, chloramphenicol, terramycin, neomycin, and tetracycline were isolated

    General Characteristics of Antimicrobial Drugs

    • Selective toxicity - the ability of a drug to kill or inhibit a pathogen while damaging the host as little as possible.
    • Therapeutic dose - the drug level required for effective clinical treatment
    • Toxic dose - the drug level at which the drug becomes too toxic for the patient (causing side effects).
    • Therapeutic index - the ratio of the toxic dose to the therapeutic dose; a higher index indicates the drug is more selective

    Dilution Susceptibility Tests

    • Involves inoculating media with different drug concentrations.
    • Broth or agar with the lowest concentration showing no growth is the MIC
    • Tubes showing no growth in broth can be subcultured into a drug-free medium
    • Broth from which the microbe can't be recovered is the MLC

    Disk Diffusion Tests

    • Disks impregnated with specific drugs are placed on agar plates inoculated with the test microbe.
    • Drug diffuses from the disk into the agar, setting up a concentration gradient.
    • Clear zones (no growth) around disks are observed

    Kirby-Bauer Method

    • Standardized method for carrying out disk diffusion tests.
    • Sensitivity and resistance are determined using tables correlating the zone diameter with the degree of microbial resistance.
    • Table values are plotted and used to estimate if the drug concentration in the body will be effective.

    Measuring Antimicrobial Sensitivity, E Test

    • Similar to disk diffusion tests but uses strips instead of disks.
    • E-test strips contain a gradient of an antibiotic.
    • The intersection of the elliptical zone of inhibition with the strip indicates the MIC.

    Measurement of Drug Concentrations in the Blood

    • Concentration of drug at the infection site must be above the MIC to be effective.
    • Microbiological, chemical, immunological, enzymatic, or chromatographic assays can determine drug concentration in the blood.

    Mechanism of Action of Antimicrobial Agents

    • Can impact pathogens by targeting functions necessary for reproduction or survival.
    • Targeted function is specific to the pathogen → higher therapeutic index

    Modes of Antimicrobial Action

    • Inhibition of cell wall synthesis (Penicillins, cephalosporins, bacitracin, vancomycin)
    • Inhibition of protein synthesis (chloramphenicol, erythromycin, tetracyclines, streptomycin)
    • Inhibition of nucleic acid replication and transcription (quinolones, rifampin)
    • Injury to the plasma membrane (polymyxin B)
    • Inhibition of the synthesis of essential metabolites (sulfanilamides, trimethoprim)

    Competitive Inhibitors (Sulfonamides)

    • Inhibit folic acid synthesis
    • Broad-spectrum

    Factors Influencing the Effectiveness of Antimicrobial Drugs

    • Ability of drug to reach the site of infection
    • Susceptibility of the pathogen to the drug
    • Drug ability to reach concentrations in the body that exceed the MIC of the pathogen

    Ability of Drug to Reach Site of Infection

    • Depends partly on the mode of administration
    • Oral drugs may be destroyed by stomach acid
    • Topical drugs target the skin's surface
    • Parenteral routes (injections) are non-oral and the drug may be excluded by blood clots or necrotic tissue

    Inhibitors of Cell Wall Synthesis (Penicillins)

    • Most are 6-aminopenicillanic acid derivatives
    • Differ in side chains attached to the amino group
    • Crucial feature is the β-lactam ring (essential for bioactivity)
    • Many penicillin-resistant organisms produce β-lactamase which hydrolyzes the bond in the β-lactam ring

    Mode of Action of Penicillins

    • Blocks the enzyme that catalyzes transpeptidation (cross-link formation in peptidoglycan)
    • Prevents synthesis of complete cell walls leading to cell lysis
    • Acts only on growing bacteria that are synthesizing new peptidoglycan

    Cephalosporins

    • Structurally and functionally similar to penicillins
    • Broad-spectrum antibiotics suitable for patients allergic to penicillin
    • Four categories based on their spectrum of activity

    Vancomycin and Teicoplanin

    • Glycopeptide antibiotics
    • Inhibit cell wall synthesis
    • Important for treating antibiotic-resistant staphylococcal and enterococcal infections
    • Previously considered a last resort drug due to the risk of resistance

    Protein Synthesis Inhibitors

    • Many antibiotics bind specifically to the bacterial ribosome (30S or 50S subunit).
    • Other antibiotics inhibit steps in protein synthesis (aminoacyl-tRNA binding, peptide bond formation, mRNA reading, translocation).

    Nucleic Acid Synthesis Inhibition

    • Variety of mechanisms to block DNA replication (inhibition of DNA polymerase, DNA helicase), and transcription (inhibition of RNA polymerase)
    • Drugs are not selective because bacteria and eukaryotes do not greatly differ in how they synthesize nucleic acids

    Antifungal Agents

    • Nystatin (mycostatin): Treats yeasts
    • Griseofulvin (Grisactin): Treats dermatophyte fungi
    • Amphotercin B (Fungizone): Treats systemic fungi

    Superinfection

    • Development and spread of drug-resistant pathogens, potentially caused by drug treatment; destroys drug-sensitive strains
    • Example: pseudomembranous enterocolitis - treatment with antibiotics kills intestinal flora, leaving Clostridium difficile to flourish and produce a toxin

    Preventing Emergence of Drug Resistance

    • Use drugs in high concentrations when required
    • Administer two or more drugs simultaneously when needed
    • Use drugs only when necessary/indicated
    • Continued development of new drugs
    • Use bacteriophages to treat bacterial disease

    Antiviral Drugs

    • Relatively few because it's hard to specifically target viral replication

    Amantadine

    • Used to prevent influenza infections
    • Blocks penetration and uncoating of the influenza virus

    Other Antiviral Agents

    • Acyclovir, Foscarnet, Cidofovir: Inhibit herpes virus enzymes involved in DNA and RNA synthesis and function. Broad-spectrum anti-DNA virus drugs inhibit viral DNA polymerases and affect papovaviruses, adenoviruses, herpesviruses, other viruses, etc.

    Anti-HIV Drugs

    • Reverse transcriptase (RT) inhibitors (nucleoside and non-nucleoside RT inhibitors) mimic peptide bonds normally targeted by proteases)
    • Protease inhibitors, which mimic peptide bonds attacked by HIV proteases
    • Fusion inhibitors, prevent HIV entry into cells

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    Antibiotic Drug Information PDF

    Description

    Explore the history and discovery of chemotherapeutic agents, including antibiotics and sulfa drugs. Learn about key figures such as Paul Ehrlich and Alexander Fleming, who played significant roles in advancing treatment methods for infectious diseases. Test your knowledge of how these chemical agents work and their impact on medicine.

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