Antimicrobials Flashcards
List the properties of antibiotics we need to know prior to prescribing
- Effect on bacteria – bactericidal vs bacteriostatic
- Spectrum of action – narrow vs broad
- Effect on pt cells – non toxic
- Route of administration – oral vs IV
- Duration of action – short / long acting
- Route of excretion/metabolism – caution with liver / kidney disease
- Interactions with other drugs – warfarin most common
- Side effects – Alcohol / allergies / staining teeth
- Resistance
What is the difference between bactericidal vs bacteriostatic antibiotics?
Bactericidal – kills bacteria
Bacteriostatic – stops bacterial replication (allowing the immune system to mop up remaining cells).
What is the difference between narrow and broad spectrum antibiotics?
Spectrum is the range of different species of bacteria that an antibiotic will kill.
Narrow- only kills / stops replicating a narrow range whereas broad spectrum kills a wider range (mixed group of species).
What is antibiotic resistance?
When a species of bacteria is resistant to the effects of a certain antibiotic and replicates without competition (because the other bacterial species will have been wiped out due to the antibiotic)
e.g. B-lactam ring in penicillin structure – cause of resistance in a lot of bacteria. B-lactamase is produced by bacteria helping resistance by splitting the b-lactam ring in penicillin structure allowing resistance.
Clostridium difficile superinfection caused can lead to _____________________. How does this occur?
pseudomembranous colitis.
- C. Diff bacteria normally lives in the gut without damaging the body but when pt is treated with broad spectrum Abx (e.g. amoxicillin, clindamycin, cephalosporins, ampicillin) all the bacteria in the gut is wiped out except the C.diff allowing it to thrive without competition).
- Causes pseudomembranous plaques – can be fatal as gut wall destroyed and pt may get sepsis.
What causes penicillin allergy?
The structure of penicillins include almost the same R1-side chain (b-lactam and thiazolidine ring) therefore being allergic to one type of penicillin will cause allergy to another type.
*may also be allergic to cephalosporins - Abx with similar structure to penicillin.
Other than allergy to Abx, what other side effects can occur in the body?
- Hearing loss (ototoxicity)
- Liver damage (hepatotoxic- damage to hepatocytes as Abx metabolised in liver)
- Kidney damage (nephrotoxic – kidney susceptible as Abx excreted in kidney)
- Teeth staining permanently (e.g. tetracycline prescribed when adult teeth forming) - Abx concentrated in bone / teeth
Why is route of administration an important consideration for Abx?
o Some drugs better delivered via IV and some better orally.
o Pts ability to swallow tablets – e.g. Floor of mouth infections prevention swallowing of medication so IV may be more appropriate.
Why is duration of Abx important?
The longer acting Abx the better (so pts don’t have to take them as often)
But Abx often given frequently up to 3-4x/day
How does a patients MH effect Abx prescription when considering excretion/metabolism?
Kidney disease – may not be able to handle larger doses of Abx
Liver disease – may not be able to metabolise certain types of Abx = further damage.
What is the effect of some Abx on Warfarin?
Warfarin – anti-coagulant
- Some Abx make Warfarin more effective – pt will therefore bleed for longer e.g. xla / fall over causing a bleed.
- Some Abx make Warfarin less effective – may develop a blood clot = myocardial infarction.
Describe the structure of bacterial cells allowing them to survive and replicate.
- Bacterial cell contains DNA which needs to be replicated to survive and multiply.
- RNA is produced by ribosomes to manufacture proteins
- To continue replicating DNA, cells need to be able to absorb and metabolise folate & other vitamins
- Cell membrane to maintain osmolarity & water content
- Cell wall – fend off immune responses of host
Describe the mechanism of action & side effects of metronidazole.
- Inhibit DNA replication & degrades existing DNA
- Effective for anaerobic infections
- Action: bacteriocidal
- *Interacts with alcohol (prevents metabolites of alcohol being destroyed resulting in side effects like severe nausea, flushing, vomiting)
Describe the mechanism of action & side effects of Macrolides (such as erythromycin, clarithromycin, azithromycin)
- Interference with ribosome function – binds 50S ribosome subunit. Prevents protein synthesis.
- Action: bacteriostatic. Broad spectrum.
- Side effects: GI disturbance (diarrhoea, nausea)
Describe the mechanism of action & side effects of Tetracycline, oxytetracycline, doxycycline.
- Interference with ribosome function – binds 30S ribosome subunit. Prevents protein syn.
- Action: mixed – bacteriostatic & bactericidal.
- Broad spectrum.
- Side effects: deposited in growing bones & teeth – staining of teeth
*Often prescribed for pts with acne
