Antibiotics Flashcards
Uses of antibiotics
- Drugs used to treat bacterial infections
- Widely used and misused drugs
- In hospitals, they acquire 30% of the drug budget
- 80% of human use in the community:
- > 50% is for respiratory infections
- > 15% is for urinary tract infections
What are antibiotics?
- Natural products: fungi and bacteria that live in the soil dwellers.
- These organisms are used to coexisting with other microorganisms, so they developed mechanisms which produce compounds that inhibit the growth of other microorganisms.
- Able to collect these products by fermentation and then chemically modify them, so they are more suitable for pharmacological properties.
How are scientists able to get antibiotics? What do they do to antibiotics?
Scientists are able to collect these products by fermentation and then chemically modify them, so they are more suitable for pharmacological use:
- They increase their pharmacological properties
- They increase their antimicrobial effect
- Need to make sure they are not toxic, not metabolised too quickly and doesn’t bind protein in the blood so it can be free in the blood - this reduces the dose.
Example of synthetic antibiotics
Most antibiotics are derived from natural products, some are totally synthetic such as sulphonamides
Discovery of antibiotic penicilin
- Alexander Fleming’s original culture of Staphylococcus aureus was contaminated with penicillium notatum
- Diffusion of the penicillin into agar caused lysis of the bacteria
- This lead to the discovery of the antibiotic penicillin
Priniciples of antibiotics as therapeutic agents
- Selective toxicity
- Therapeutic margin
Selective toxicity of antibiotics
- This means the antibiotic should be able to kill the bacteria without harming the host cells.
- This is able to happen because bacteria and human cells have different structures, an antibiotic can be made to target the cell wall of a bacteria so not to harm the host.
- More difficult in anti-viral because viruses are intracellular hosts which means they integrate within the human genome.
Therapeutic margin of antibiotics
- This is the balance of the antibiotic between being sufficient at treating the bacterial infection and becoming toxic to the host.
- It is the active dose which is the MIC (minimum inhibitory concentration) which is the concentration needed to see an active effect of the drug.
- Some antibiotics are safe so you can increase the dose by a lot and no toxic effect will be seen, however some antibiotics are very toxic so the MIC and toxic dose are very close.
- When a drug is described as being safe it means, they have a wide therapeutic effect and vice versa.
How do antibiotics disturb the natural flora?
- The natural flora is maintained because each microbe keeps the other one in balance by producing something that inhibits the growth of another.
- e.g. in the gut - when the balance is disturbed, this is when disease occurs because one microbe grows to form colonies.
- For example Clindamycine and broad spectrum beta lactams are used leading to the overgrowth of C. dif which is a gram +ve spore forming bacteria, leading to diarrhoea, ulceration and inflammation.
How are antibiotics classified?
- By type of activity
- Structure
- Target site of activity
What are the types activity of antibiotics?
Used in different scenarios -
- Bacteriostatic: inhibit the bacteria from growing e.g. when a patient is not immunocompromised and there not used for emergency use. Need a higher dose to be able to kill the bacteria (toxic dose)
- Bacteriocidic: actively kills the bacteria e.g. used when a patient is immunocompromised and therefore can be used for emergency, the MIC and the toxic dose are very close and therefore it can be used to kill the bacteria.
How does the structure of antibiotics effect?
- Some antibiotics have specific structures, which help them target the bacteria they are killing
- E.g. beta lactams antibiotics have a beta lactam ring in their structure which means they are able to act as competitive substrates for the enzymes involved in the bacterial cell wall.
- Therefore, when a bacteria is resistance, it means they have enzymes which are able to breakdown the beta lactam ring in the antibiotic so it no longer has a therapeutic effect.
Broad specturm antibiotics
Able to work on multiple different bacteria and overuse of this means resistance can occur
Narrow spectrum
- Antibiotics that can only work on certain bacteria and therefore need to know what bacterial infection it is to administer the drug.
Cephalosporins
Generation of modified antibiotics each with a different chemical modification which is suited to certain types of bacteria
The modification target different types of bacteria, due to different types of bacteria having different structures