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Questions and Answers

What is the primary function of the bacterial cell wall?

Protection from damage and maintaining osmotic pressure (correct)

Replication of DNA

Nutrient absorption

Energy generation

Which of the following is a characteristic of gram-negative bacteria?

Presence of peptidoglycan

Synthesis of folate from amino acids

Absence of an outer membrane

Outer membrane preventing penetration of some agents (correct)

What does sulfanilamide mimic in the process of folate synthesis?

Amino acids

Paraaminobenzoic acid (PABA) (correct)

Tetrahydrofolate

Pteridine

What type of bacteria does not have an outer membrane?

Gram-positive bacteria Signup and view all the answers

Why should sulfonamides be avoided in patients with G6PD deficiency?

They induce oxidative stress and hemolytic anemia Signup and view all the answers

What type of reactions does Class II biochemical reactions in bacteria primarily utilize?

Energy (ATP) and simple carbon compounds to produce small molecules Signup and view all the answers

What is classified as a bacteriostatic agent in the context of folate synthesis inhibition?

Sulfamethoxazole Signup and view all the answers

During which physiological condition should sulfonamides be used with caution?

Only if potential benefit outweighs risk during pregnancy Signup and view all the answers

What is a notable toxic reaction associated with sulfonamides?

Crystalluria Signup and view all the answers

Which substance is necessary for bacteria to convert dihydrofolate to its active form?

Dihydrofolate reductase Signup and view all the answers

What is the primary mechanism through which trimethoprim functions?

Inhibits dihydrofolate reductase Signup and view all the answers

Which condition can trimethoprim treatment lead to, requiring preventive measures?

Megaloblastic anemia Signup and view all the answers

How do glycopeptides like vancomycin function in relation to bacterial cells?

By inhibiting glycopeptide polymerization Signup and view all the answers

What type of organisms typically have a thicker cell wall composed of peptidoglycan?

Gram-positive organisms Signup and view all the answers

Which is a potential serious side effect of using sulfonamides?

Stevens-Johnson syndrome Signup and view all the answers

Which of the following statements regarding vancomycin is accurate?

It is primarily excreted through the kidneys. Signup and view all the answers

Which aminopenicillin is better absorbed orally and not affected by food?

Amoxicillin Signup and view all the answers

What type of penicillins are Ticarcillin and Piperacillin classified as?

Antipseudomonal penicillins Signup and view all the answers

Which cephalosporin is mentioned as being more active against Pseudomonas aeruginosa than Ticarcillin?

Piperacillin Signup and view all the answers

In which scenario should ceftriaxone be avoided?

In premature neonates with jaundice Signup and view all the answers

Which class of antibiotics is known for being principally excreted renally, requiring dose modification in renal impairment?

Cephalosporins Signup and view all the answers

Which of the following cephalosporins is NOT active against Pseudomonas aeruginosa?

Ceftaroline Signup and view all the answers

What is a principal side effect of cephalosporins?

Hypersensitivity reactions Signup and view all the answers

Which of the following beta-lactamase inhibitors is NOT mentioned as effective against carbapenemase?

Clavulanic acid Signup and view all the answers

What is the cause of grey baby syndrome in premature neonates?

Inability to excrete chloramphenicol due to underdeveloped UDP-glucuronyl transferase Signup and view all the answers

Which of the following correctly describes the action of clindamycin?

Inhibits protein synthesis by binding to the 50S subunit of the bacterial ribosome Signup and view all the answers

What is a significant risk associated with clindamycin treatment?

Severe skin reactions including toxic epidermal necrolysis Signup and view all the answers

What mechanism do streptogramins use to exert their antibacterial effect?

Block the translation of mRNA into protein by binding sequentially to the 50S ribosomal subunit Signup and view all the answers

Which of the following are binding sites present in the ribosome's 50S subunit for tRNA?

All of the above Signup and view all the answers

Which condition must be monitored when using clindamycin?

Hepatic impairment and abnormalities Signup and view all the answers

What is the primary mode of action of tetracyclines in protein synthesis inhibition?

They bind to the 30S ribosomal subunit. Signup and view all the answers

What types of bacteria are streptogramins effective against?

MRSA and vancomycin-resistant enterococcus faecium Signup and view all the answers

Which of the following conditions must be observed when prescribing tetracyclines?

Should not be administered to children under 12. Signup and view all the answers

Why should clindamycin not be used for CNS infections?

It has poor penetration into cerebrospinal fluid Signup and view all the answers

Which statement about linezolid is true?

It is useful for treating infections caused by methicillin-resistant Staphylococcus. Signup and view all the answers

What factors can impair the absorption of tetracyclines?

Consumption of dairy products. Signup and view all the answers

What is the mechanism of action of aminoglycosides in protein synthesis inhibition?

They distort the structure of the 30S subunit. Signup and view all the answers

Why are aminoglycosides poorly absorbed from the gastrointestinal tract?

They are highly polar cations. Signup and view all the answers

Which of the following statements about aminoglycosides is true?

They should be given parenterally for systemic therapy. Signup and view all the answers

What should be avoided when using aminoglycosides to prevent ototoxic effects?

Use with diuretics like furosemide. Signup and view all the answers

What is the primary action of fusidic acid in bacteria?

Binds to the 50s ribosomal subunit Signup and view all the answers

Which mechanism is NOT associated with nucleic acid synthesis inhibition?

Altering lipid synthesis Signup and view all the answers

What is a caution for the use of ciprofloxacin?

It may induce seizures in patients with epilepsy Signup and view all the answers

What type of bacteria is fusidic acid primarily effective against?

Gram-positive bacteria Signup and view all the answers

Which statement about quinolones is correct?

They inhibit DNA gyrase Signup and view all the answers

Which of the following is a contraindication for ciprofloxacin?

G6PD deficiency Signup and view all the answers

Which of the following side effects is associated with ciprofloxacin?

Prolonged QT interval Signup and view all the answers

What effect do antacids have when taken with quinolones?

They interfere with quinolone absorption Signup and view all the answers

Study Notes

Antimicrobial Chemotherapy

Antimicrobial Chemotherapy is the use of drugs to treat infections caused by microorganisms or cancer.
Antibiotics are natural substances produced by microorganisms that suppress the growth or kill other microorganisms at low concentrations.
Chemotherapy relies on the principle of selective toxicity, exploiting metabolic or structural differences between normal and pathogenic cells.

Outline

Introduction to Chemotherapy
Activity/Spectrum of Antimicrobial Agents (AMAs)
Classification of AMAs
Problems with AMAs
Selection of AMAs
Combination of AMAs
Failure of AMAs

Antimicrobial Activity

Cidal (bacteriocidal, vermicide, fungicidal, virucidal) : The drug kills susceptible organisms, reducing the number of viable organisms quickly after exposure.
Static (bacteriostatic, vermifuge, fungistatic, virustatic): The drug inhibits the organisms' growth, keeping the number of viable organisms relatively constant. Host immune responses are then needed to eliminate the organisms.

Antimicrobial Spectrum

Narrow spectrum: Active against a single species or limited group of pathogens, used when the causative pathogen is known and the infection is not severe.
Broad spectrum: Active against a wide range of pathogens, preferred when the causative pathogen is unknown or the infection is severe.

Classification of AMAs

Chemical structure: beta-lactams, triazoles, etc.
Type of action (Cidal or Static): Bacteriostatic, bactericidal, fungicidal, fungistatic, viricidal, etc.
Type of Organism (primary active against): Antibacterial, antiviral, antifungal, antiprotozoal, antihelminthic

Sources

Fungi: penicillins, griseofulvin
Bacteria: polymyxin B, bacitracin, colistin, Actinomyces: amphotericin B, aminoglycosides, macrolides, tetracyclines, polyenes

Mechanism/Site of Action

Protease inhibitors, Integrase inhibitors, Cell wall inhibitors, Protein synthesis inhibitors, Nucleic acid synthesis inhibitors etc.

Problems with AMAs

Toxicity

Local toxicity: effects at the site of administration, (e.g., gastric irritation, pain, abscess, thrombophlebitis).
Systemic toxicity: dose-related organ damage (e.g., tetracycline - discoloration of teeth, aminoglycosides – nephrotoxicity and ototoxicity, chloramphenicol - grey baby syndrome).

Hypersensitivity reactions

Inappropriate or exaggerated responses to an antigen or allergen (unrelated to dose)
e.g., Penicillin, Nevirapine, Clindamycin

Superinfection

New infection in a patient with existing infection, often occurring due to use of AMAs (mostly in immunocompromised patients).
e.g., Bacterial superinfection in viral respiratory disease, Infection of a chronic hepatitis B carrier with hepatitis D virus.

Drug Resistance

Natural/Intrinsic Resistance: Some microbes have in-built resistance to specific AMAs. (e.g., Gram-negative bacilli, M. tuberculosis)
Acquired Resistance: Microorganisms develop resistance mechanisms/genes due to exposure to AMAs.

Selection of AMAs

Patient-Pathogen-Drug Relationship
Pharmacokinetics (drug effect on patient)
Pharmacodynamics (patient effect on drug)
Immunity (patient effect on pathogen)
Sepsis (pathogen effect on patient)
Selective toxicity (drug effect on pathogen)
Resistance (pathogen effect on drug)

Age: avoiding certain AMAs in children (e.g., tetracycline)
Renal and hepatic function: careful use of aminoglycosides, erythromycin and tetracyclines in patients with impaired renal or liver function.
Drug allergy: avoid AMAs to which the patient is allergic.
Patient immunity: limiting use of broad-spectrum AMAs in immunocompromised patients.
Pregnancy: exercise caution with certain AMAs.
Genetic factors: consideration of G6PD deficiency when prescribing certain AMAs (e.g., sulphonamides).

Type of activity (systemic vs. non-systemic)
Spectrum of activity (narrow vs. broad)
Sensitivity of the organism (MIC, MBC)
Pharmacodynamic profile (side effects, adverse effects)
Pharmacokinetic profile (ADME)
Route of administration (enteral, parenteral, topical)
Cost (cost-effectiveness)

Clinical diagnosis
Selection of AMA based on microbiological examination (Antimicrobial Susceptibility Testing)

Combination of AMAs

Preventing resistance
Achieving synergism (e.g., Rifampin + isoniazid for M. tuberculosis)
Broadening antimicrobial spectrum (e.g., Cotrimoxazole)
Reducing toxicity (e.g., Amphotericin B + rifampin)

Failure of AMAs

Improper selection or dosage of AMAs
Treatment begun too late
Failure to take necessary precautions
Poor immunity
Trying to treat untreatable infections (viral infections)
Presence of dormant or altered organisms that later give risk to relapse.

Antibacterial Agents

Structure of Bacterial Cell

Cell wall (peptidoglycan): provides structural support and resistance to osmotic pressure
Cell membrane(selective permeability): essential for various nutrients.
Cytoplasm: contains macromolecules, ribosomes, and chromosome(DNA) for protein synthesis.
Outer membrane(only in gram-negative bacteria): prevents penetration of some antibacterial agents

Biochemical Reactions of Bacteria

Class I: Utilizes glucose/alternative carbon sources for energy (ATP).
Class II: Produces molecules like folate, amino acids, nucleotides, phospholipids etc using energy and simple carbon compounds.
Class III: Assembles small molecules into macromolecules (DNA, RNA, proteins, peptidoglycan)

Targets of Action of Antibacterial Agents

Folic acid synthesis
Cell wall synthesis
Protein synthesis
Nucleic acid synthesis
Formed cell (mainly cell membrane)

Folate Synthesis Inhibitors

Sulfonamides: structural analogues of PABA, competing with PABA for enzyme involved in folate synthesis.
Trimethoprim : inhibits dihydrofolate reductase enzyme in folate metabolism preventing synthesis of tetrahydrofolate (often combined with sulfonamides for synergistic effects and improved outcome)

Cell Wall Synthesis Inhibitors

Glycopeptides (Vancomycin, Teicoplanin): block glycopeptide polymerization
Beta-lactams: inhibit the final transpeptidation steps that establish cross-links of peptidoglycan by bonding to penicillin-binding proteins (PBP)
Penicillins are the most common beta-lactams, available in various types, and forms depending on their properties

Protein Synthesis Inhibitors

Tetracyclines: bind to 30S ribosome subunit disrupting the tRNA binding site (involved in translation)
Aminoglycosides: bind to 30S ribosomal subunits, impairing protein synthesis and distorting the mRNA reading frame..
Macrolides: bind to the 50S ribosomal subunit, blocking translocation and peptide chain elongation.
Chloramphenicol: binds to the 50S ribosomal subunit, preventing the formation of peptide bonds and inhibiting protein synthesis.
Lincosamides (Clindamycin): bind to the 50S ribosomal subunit, interfering with peptide bond formation.
Streptogramins (Quinupristin/Dalfopristin): combine to inhibit protein synthesis by affecting the binding site (50S ribosomal subunit).
Linezolid: binds to the 50S ribosomal subunit, interfering with protein synthesis mechanisms

Nucleic Acid Synthesis Inhibitors

Quinolones: inhibit bacterial DNA gyrase and topoisomerase IV enzymes necessary for bacterial DNA replication
Nitroimidazoles : only active in anaerobic conditions
Fusidic acid-inhibits translocation.

Formed Structure of the Cell (Cell Membrane Inhibitors)

Polymyxins: cationic detergents that have a selective effect on bacterial cell membranes, interacting with phospholipids and disrupting structure.

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