Antibiotics Flashcards
What are antibiotics?
Natural products of fungi and bacteria derived from fermentation that are chemically modified to increase microbial effect and pharmacological properties
What are the key principles of antibiotics as therapeutic agents?
Selective toxicity
Therapeutic Margin
Why is selective toxicity import for antibiotics?
Harm microorganisms not the host due to differences in structure and metabolic pathways between host and pathogen
Variation between microbes
Effect on commensals - can be servere
Why is a therapeutic margin important for antibiotics?
Active dose (MIC) vs toxic effect
Narrow for toxic drugs
NO SAFE DRUG
What is microbial antagonism?
Limits growth of competitors and pathogens
Maintains flora - complex interactions
Competition between flora
What is meant by “loss of flora”?
Bacterial or pathogen overgrowth
Eg. Antibiotic associated colitis - clostridium difficile overgrowth
How is bacterial clearance achieved?
Antibiotic AND immunity
Immunosuppressed patients are treated slightly differently
What are the three ways antibiotics can be classified?
Type of activity - bactericidal and bacteriostatic
Structure
Target site for activity
What is meant by bactericidal functioning antibiotics?
Kill bateria
Used when the host defence mechanisms are impared
Required in endocarditis, kidney infection
What is meant by bacteriostatic functioning antibiotics?
Inhibit bacteria
Used when the host defence mechanisms are intact
Used in many infectious diseases
What are the two types of spectrum of activity for antibiotics?
Broad spectrum antibiotics - effective against many types
- eg. Cefotaxime
Narrow spectrum antibiotics - effective against very few types
- eg. Penicillin G
What are 5 types of penicillin?
Basic penicillins
Eg. PenG - not acid stable so cannot be taken orally
Anti-staphylococcal penicillin’s - beta lactimase resistant - less potent than penG
Eg. Flucloxacillin - oral administration
Broader spectrum penicillins
Eg. Ampicillin
Anti-pseudomonas penicillins
Eg. Piperacillin
Beta-lactam/beta-lactamase inhibitor combinations
Eg. Augmentin
How can antibiotics be classified by molecular structure?
Structure mimics of natural substrates for enzymes
Beta lactams - have a beta lactam ring
- penicillin’s
- cephalosporins
What are the most common modes of action for antibiotics?
Cell wall synthesis - beta lactams
- penicillins
- cephalosporins
Folic acid metabolism
- trimethoprim
Cell membrane
- colitis - polymyxins
Protein synthesis - 50s inhibitors
- erythromycin
- linezolid
Protein synthesis - 30s inhibitors
- tetracycline
- doxycycline
DNA and RNA processes
- quinolones
Free radicals
- metronidazole
MUST LEARN EXAMPLES
Describe the cell wall inhibitors reaction pathway
Gram positive - penetrate the cell wall and inhibit peptidoglycan
Gram-negative - penetrate plasma bi layer using pores and inhibit peptidoglycan - some cell wall inhibitors cannot work
