Penicillins Flashcards
Usual Amoxicillin dose?
500mg every 8 hours, or 1g twice a day
Name 2 reasons to adjust the dose of amoxicillin
- in severe infections - 1g every 8 hours can be used
- in renal impairment need to reduce dose if CrCl is <30
Most common ADRs of amoxicillin?
Diarrhoea, nausea, rash
MOA of amoxicillin?
Forms a covalent bond with PBP, inactivating it. Prevents cell wall synthesis by preventing the cross linking of peptidoglycan chains
Most common dose of Amoxicillin / clavulanate?
500 - 875mg every 12 hours for 5-10 days depending on infection
Clavulanic acid = 125mg
MOA of clavulanic acid?
Inhibits B-lactamase - the enzyme responsible for breaking down B-lactams.
Purpose of adding clavulanic acid to amoxicillin?
Extends its activity - includes more gram negative
ADRs associated with clavulanic acid?
Cholestatic hepatitis
Indication for flucloxacillin?
Staph, pneumonia, wounds, etc
When should you reduce the dose of flucloxacilin?
When CrCl is less than 10
Usual dose of flucloxacillin?
250-500mg every 6 hours. Max of 4g a day
When to take flucloxacillin in relation to food?
Best absorbed on empty stomach. Half an hour before food or 2 hours after
Indications of phenoxymethylpenicilin?
Tonsillitis, rheumatic fever, etc
Dose of phenoxymethylpenicilin
250-500mg every 6 hours. Maximum 3g daily
When for tonsillitis to prevent rheumatic fever, 500mg bd for 10 days
Which bacteria is metronidazole most effective against?
Anaerobic bacteria such as c. Diff
Penicillins ADRs?
Pain at injection site, GIT affects, electrolyte disturbances, rash
Main groups of bacteria that amoxicillin is effective against?
Gram positive and anaerobes
Amoxicillin can be used for CAP. What is the most common causative organism
Streptococcus pneumoniae
Monitoring required for penicillins?
Monitor hepatic and renal function if Tx duration is longer than 10 days
Amox + clav can be used for HAP. What is the main causative organism
Gram negative - pseudomonas aeruginosa
Max dose of Amox + Clav?
2g q6h for severe infections
When should Amox+clav be taken with respect for food?
Take with food
IV dosing of flucloxacillin?
1-2g every 6 hours, max = 12g (severe infections like staphylococcus pneumonia)
Common causative organism for skin infections that flucloxacillin is used for?
Staphylococcus epidermidis
Spectrum of flucloxacillin vs amoxicillin?
More narrow
ADR unique to flucloxacillin?
Increase in liver enzymes and cholestatic hepatitis
Main indication for phenoxymethylpenicilin?
Tonsillitis or pharyngitis caused by strep. Pyogenes
Treatment for s. Pyogenes tonsillitis?
Phenoxymethylpenicilin
500mg bd for 10 days
Dose of phenoxymethylpenicilin can be up to 500mg q6h (max 3G daily)
10 day Tx course is to eradicate s. pyrogenes and prevent development of acute rheumatic fever
ADRs for phenoxymethylpenicilin?
Same as other penicillins
When might antibiotics not be indicated for strep. Tonsillitis ?
When the case is mild and in a community with low risk of rheumatic fever.
If risk is high, phenoxymethylpenicilin is used to prevent development of rheumatic fever
Should phenoxymethylpenicilin be taken with or without food
Without
First line treatment for sinusitis?
Symptomatic Tx
If persisting for more than 7 days or if there is a fever, first line is amoxicillin (typical pathogen is s. Pneumonaie)
Name 2 alternatives to phenoxymethylpenicilin for s. Pyogenes
Mild = cefalexin
Severe= Azithromycin, clarithromycin
Name 2 alternatives to amoxicillin for CAP
Doxycycline or clarithromycin
Antibiotics useful for MRSA?
Resistant to all B-lactams except newest cephalosporins like ceftaroline
Can use= vancomycin, doxycycline, trimethoprim / sulfamethoxazole
Alternatives to flucloxacillin for staph?
Cefalexin or clindamycin or trimethoprim with sulfamethoxazole
