Infection Flashcards
What is an example of a cephalosporin?
Cefalexin
What is the mechanism of action of Cefalexin?
Interfere with synthesis of bacterial cell wall peptidoglycan (bactericidal)
What are the 3 beta-lactam classes?
- Penicillins
- Cephalosporins
- Carbapenems
When are cephalosporins used?
- Septicaemia
- Pneumonia
- Meningitis
- Biliary infections
- UTIs (in pregnancy)
- Sinusitis
Often need individual sensitivity testing
What are two examples of macrolides?
- Azithromycin
* Clarithromycin
What is the mechanism of action of macrolides?
Inhibit bacterial protein synthesis - effect ribosomal translocation (bactericidal/bacteriostatic)
When are macrolides used?
Macrolides are similar to penicillins (so clarithromycin is useful in penicillin allergies)
Atypical respiratory pathogens
Give 4 examples of penicillins.
- Amoxicillin
- Flucloaxcillin
- Co-amoxiclav
- Phenixymethylpenicillin (Penicillin V)
What is the mechanism of action of penicillins?
Interfere with synthesis of bacterial cell wall peptidoglycan (bactericidal)
What is an example of a quinolone?
Ciprofloxacin
What is the mechanism of acton of ciprofloxacin?
Inhibits topoisomerase II (bacterial DNA gyros) - inhibits transcription/replication
When is ciprofloxacin often used?
Good against gram negative organisms, gram postitoves and atypical
- Complicated UTIs
- Psuedomonas aeruginosa
- Gonorrhoea
What are some ADRs of ciprofloxacin?
- Tendinitis +/- rupture
- Aortic dissection
- Central nervous system effects (inc. convulsions)
What is an example of a tetracycline?
Doxycycline
What is the mechanism of action of doxycycline?
Inhibits protein synthesis - bind to bacterial ribosomes and prevent tRNA from binding, so prevents the initiation (bacteriostatic)
When is doxycycline used?
Orally only
- Atypical respiratory infections
- Acne
- Chlamydia
- Lyme disease
What’s a key fact to remember about doxycycline?
Shouldn’t be given to under 12s, pregnant or breastfeeding women
What is the mechanism of action of trimethoprim?
Folate antagonist - prevents bacterial nucleic acid and protein synthesis
When is trimethoprim used?
UTIs but be careful with females of reproductive age (teratogenic)
What kind of bacteria is metronidazole good against?
Anaerobic bacteria
Why should you definitely avoid alcohol if taking metronidazole?
Has a disulfiram like action - hangover effects
What is an example of a nitofuran?
Nitrofurantoin
What is the mechanism of action of nitrofurantoin?
Reduced to reactive intermediates by nitrofuran reductase in bacteria - intermediates then attack ribosomal and DNA proteins and inhibit the citric acid cycle
Why is nitrofurantoin best for use in UTIs?
Up to 50% of an oral dose of nitrofurantoin is excreted in the urine in it’s unchanged form - can concentrate in the urine so more effective in the bladder, etc
What is the suggested metronidazole mechanism of action?
Metabolised to it’s active form by anaerobes and protozoa - blocks nucleic acid synthesis
Give an example of an antiviral agent
Aciclovir
What is the mechanism of action of aciclovir?
Mostly activated in infected cells (thymidine kinase - viral enzyme, is good at activating aciclovir) - then it inhibits viral DNA polymerase
When is aciclovir used?
- Herpes simplex infections - genital herpes, encephalitis
* Varicella Zoster - chicken pox, shingles
When should you use aciclovir in herpes?
If genital - use within 5 days of start of an episode/while new lesions are forming (don’t use topical) and then use for longer if have recurrent episodes
If oral - not suggested unless clinical judgements suggests otherwise or immunocompromised patient
Is metronidazole a CYP inhibitor or inducer? And of which CYP enzyme?
Inhibitor of CYP2C9
Are macrolides CYP inhibitors or inducers? And of which CYP enzyme?
Inhibitors of CYP3A4
What’s a DDI to consider with oral antibiotics and oral contraception?
That the antibiotics will reduce the gut flora so reduce enterohepatic circulation/recycling of drugs, so lower blood concs of the pill, increased risk of getting pregnant
