MICROBIOLOGY Flashcards
What is the normal range for WCC?
4 - 11 x 109/L
What is the normal range for neutrophils?
2.0 – 7.0 x 109/L
When CRP (C-reative protein) is raised this indicates infection.
It is released into the body from the liver in response to inflammation
ESR (erythrocyte sedimentation rate) is used to detect inflammation in the body.
An ESR test can monitor inflammatory conditions, such as rheumatoid arthritis or systemic lupus erythematosus
What is an MSU?
midstream specimen of urine
Used to detect infection
What kind of antitbiotic is Gentamicin and what is its mechanism of action?
Aminoglycoside
Bind irreversibly to the 30S subunit of bacterial ribosomes and inhibit protein synthesis
What are ahminoglycosides active against?
Gram negative, anaerobic bacteria, staphylococci and mycobacteria
Aminoglycosides can impair neuromuscular transmission so should not be given to people with m_______ g______
Myasthenia Gravis
Ototoxicity caused by ahminoglycosides can be enhanced if co-prescribed with other drugs causing this such as ?
Loop diuretics- furosemide
Vancomycin
Vancomycin is a glycopeptide used to treat mainly gram ______ bacteria such as Endocarditis/ MRSA.
Gram POSITIVE
Aerobic and anaerobic gram positive bacteria
(gent= negative, vanc= positive)
What antibiotics do we use in the treatment of C.diff?
Metronidazole first line
Vancomycin oral second line
What is Vancomycins mechanism of action?
Its a GLYCOPEPTIDE
It inhibits growth and cross-linking of peptidoglycan chains- inhibiting the cell wall synthesis in gram positive bacteria.
It is inactive against gram negative bacteria which have a difference cell wall structure containing lipopolysaccharides
Note: Teicoplanin is also a glycopeptide that has a spectrum of activity and mechanism very similar to vanc
What can happen if vancomycin is infused too rapidly?
RED MAN SYNDROME
Erythema, hypotension, bronchospasm
vancomycin must therefore be given as a slow IV infusion (NOT IV bolus or IM Injection) infuse over at least 60 minutes
What do we commonly see prescribed for CAP?
Amoxicillin 1g TDS + Clarithromycin 500mg BD
Can add in Vancomycin third line
What do we commonly see prescribed for HAP?
Amoxicillin 1g TDS + Gentamicin (for pseudomonas cover/ gram negative)
Stepdown to co-amoxiclav
Metronidazole is commonly used to treat anaerobic bacterial infections such as?
oral infections (dental abscess) Tonsillitis/ quinsy aspiration pneumonia C.diff Gyneacologic infections: Pelvic Inflammatory disease
All the above involve ANAEROBIC bacteria
What is metronidazole mechanism of action?
It works in anaerobic bacteria. It is reduced inside the bacterial cell to form a toxic free radical that binds to DNA and reduces DNA synthesis.
Is metronidazole hepatically or renally cleared?
Hepatically
It should therefore not be used in people with severe liver disease
Why are anearobic bacteria often resistant to pencillins?
Due to the production of beta-lactamases
What does metronidazole interact with?
Warfarin (reduces metabolism through inhibiting CYP450)
Phenytoin
Rifampicin
lithium
What is Teicoplanins mechanism of action?
Same as vancomycin- it inhibits cross-linkage of peptidoglycan chains in bacterial cell walls and therefore inhibits their synthesis. Active against gram POSITIVE bacteria.
It is bacteriocidal- (cell wall- house analogy)
What is the basic mechanism of action of all penicillins?
Inhibit enzymes responsible for cross-linking peptidoglycan in bacterial cell walls- this weakens cell walls- water then enters, cells swell, burst and die
What structure do penicillins contain which is responsible for their activity?
A beta-lactam ring
But this is what causes resistance: bacteria can produce beta-lactamase enzymes which break this ring apart :(
When does the rash usually show up in those with a penicillin allergy following penicillin exposure?
7- 10 days after first exposure
1-2 days after repeat exposure
What do penicillins interact with?
Methotrexate- they reduce renal excretion of methotrexate leading to toxicity
Benzylpenicillin/ penicillin V are usually used for the treatment of tonsillitis/ quinsy. What dose?
Benzypenicillin (IV ONLY)- 1.2g QDS
Penicillin V (phenoxymethylpeniciilin) 500mg -1g QDS
Tazocin is an antipseudomonal penicillin. It is reserved for severe infections. It covers pseudomonas aeruginosa. What is it that makes this antibiotic active against Beta lactamase-producing bacteria?
The addition of the beta lactamase INHIBITOR tazobactam- makes it active again things like staph aureus
It should be used with caution in those at risk of C.diff
Reduce dose in moderate/ severe renal impairment
What penicillins do we use for the empirical treatment of pneumonia as they have broad spectrum of activity again gram positive and gram negative bacteria?
Amoxicillin
Co-amoxiclav
(Co-amoxiclav is just amoxicillin with the addition of clavulanic acid- a beta-lactamase inhibitor).
Broad spectrum antibiotics such as co-amoxiclav, amoxivillin, tazocin should be used with caution in those at risk of what?
C.diff
as they can wipe out gut flora an cause c.diff in these patients e.g. elderly
Broad spectrum antibiotics such as amoxicillin and co-amoxiclav can increase the anticoagulant effects of warfarin. How?
By killing normal gut flora that synthesise vitamin K
Flucloxacillin is contraindicated in patients with prior flucloxacillin-related hepatotoxicity
Short half life (45 mins) therefor QDS administration
Teicoplanin needs dose adjustment in renal impairment
Use normal dose regimen on days 1–4, then use normal maintenance dose every 48 hours if eGFR 30–80 mL/minute/1.73 m2
Use normal maintenance dose every 72 hours if eGFR less than 30 mL/minute/1.73 m2.
What antibiotic can we use for skin infections if the patient has a penicillin allergy?
Clarithromycin- a macrolide
We use clarithromycin in chest infections such as pneumonia, alongside amoxicillin. What does clarithromycin cover for?
Atypical cover
e.g. Legionella and Mycoplasma pneuoniae
What is the triple therapy for H.pylori?
Clarithromycin (macrolide)
+ Amoxicillin or Metronidazole
+ PPI
What is the mechanism of Macrolides such as clarithromycin, azithromycin and erythromycin?
Bind to the 50S subunit of bacterial ribosomes and inhibit bacterial protein synthesis
They are bacteriostatic (i.e stop growth)
What do macrolides such as clarithromycin, erythromycin PROLONG? What drugs do we therefore need to watch out for?
Prolong the QT INTERVAL
Watch out for drugs that also prolong QT interval or cause arrythmias such as amiodarone, antipsychotics, quinine, quinolone (moxifloxacin, ciprofloxacin)
What is the mechanism of action of cephalosporins such as ceftriaxone, cefalexin, cefotaxime?
Inhibit enzymes responsible for cross-linking peptidoglycan in bacterial cell walls- this weakens cell walls- water then enters, cells swell, burst and die
Same as that of penicillins and meropenem
NB: Cephaolsporins and meropenem are naturally more resistant to B-lactamases than penicillins are therefore they are reserved for very severe or complicated infections caused by antibiotic-resistant organisms
If meropenem is prescribed in those with renal impairment or in too higher doses, what do we put the patient at risk of?
CNS toxicity including seizures
Should be used with caution in patients with epilepsy
Meropenem will also reduce plasma concentration of sodium valproate
What antibiotics do we usually use for treatment of meningitis?
Cephalosporins-
Ceftriaxone or Cefotaxime IV
If patient has a penicillin allergy use Chloramphenicol
What is the mechanism of action of QUINOLONES (ciprofloxacin, moxifloxacin, levofloxacin)?
Inhibit DNA synthesis
Particularly active against gram negative bacteria but moxifloxacin and levofloxacin have developed activity against gram positive also.
What are the use of Quinolones (ciprofloxacin, moxifloxacin, levofloxacin) cautioned in?
They can lower seizure threshold so caution in EPILEPSY
Co-prescription of NSAID’s and quinolones increases seizure risk
QT PROLONGATION
Myasthenia graves
Quinolones (ciprofloxacin, moxifloxacin, levofloxacin) can produce some nasty side effects, such as?
Lower seizure threshold
Hallucination
Rupture of muscle tendons
QT interval prolongation
Why is trimethoprim contra-indicated in Pregnancy for UTI’s? What do we use instead?
It is a folate antagonist so it teratogenic in the first trimester
We should use Cefalexin for UTI’s in pregnancy
What is the rare but very serious side effect of penicillins that can occur due to cerebral irritation?
Encephalopathy
Should never be given intrathecally (into spine)
What can co-amoxiclav and flucloxacillin cause up to 2 months after use and as a result these need to be used with caution in patient with LIVER dysfunction?
CHOLESTATIC JAUNDICE
