infectious diseases Flashcards
What are the 4 types of beta lactams?
Penicillins
Cephalosporins
Carbapenems
Monobactam
Mechanism of action of beta lactams
Interfere with cell wall synthesis, are bactericidal (bacterial death)
Bind to penicillin binding protein (transpeptidase enzyme), protein cannot catalyse the cross linking of polymer chains. Cell wall is weakened, causing lysis of bacterial cell
Which drug should be used with beta lactams?
Which should not?
Aminoglycosides can use, synergistic effect, both are bactericidal
Tetracyclines should not, cos Tetracyclines are bacteriostatic
What are the 30s protein synthesis inhibitors?
What is the key difference between them?
Aminoglycosides
Tetracyclines
Aminoglycosides are bactericidal, can be used with beta lactams
Tetracyclines are bacteriostatic, cannot be used with beta lactams
Which conditions need to cover for grp A strep only?
Which antibiotics to use?
1) Non purulent ssti (cellulitis, erysipelas) - mild only
2) Pharyngitis
use Amoxicillin, Penicillin V.
If allergic to Pen V -> use Cephalexin
If allergic to Amox -> use Cefuroxime
If severe allergy -> use Clindamycin
Which conditions need to cover for both MSSA and Grp A Strep?
1) Multiple lesions of Impetigo, Ecthyma
2) Purulent SSTI (furuncles, carbuncles, skin abscess, purulent cellulitis)
Use Cloxacillin, Cephalexin
Mild allergy: use Cefuroxime
Severe allergy: Clindamycin
What are the anti-pseudomonal beta lactams? (in VAP / HAP)
Pip tazo
Ceftazidime*
Cefepime
Imipenem
Meropenem
(No Ertapenem)
Amikacin*
*cannot be used without MRSA coverage as these agents do not cover for MSSA themselves
What are the 50s protein synthesis inhibitors?
Macrolides
Clindamycin
Linezolid
Penicillin allergy (3 groups)
o Amoxicillin, Ampicillin, Cephalexin
o Cefepime, Ceftriaxone
o Ceftazidime, Aztreonam
o All penicillins, including Piptazo (for a Penicillin allergy)
Treatment flow for SSTI
(which agents to cover for beta hemolytic strep, grp A strep, mild penicillin allergy and severe penicillin allergy)
- beta hemolytic Strep (Grp A-G) only: Amoxicillin, Pen V
- MSSA only: Cloxacillin, Cephalexin
- Grp A + MSSA: Cloxacillin, Cephalexin
- If mild penicillin allergy: change Cephalexin -> Cefuroxime
- If severe penicillin allergy: change Cephalexin or Cloxacillin -> Clindamycin
Modified Centor criteria for Pharyngitis, when should we treat?
- Fever > 38 deg = (1)
- Swollen, tender anterior cervical lymph nodes = (1)
- Tonsillar exudate = (1)
- Absence of cough = (1)
- Age: 3-14yo (+1), 15 - 44 (0), 45 or older (-1)
Total points
- 0 - 1 pts: no testing needed, presume viral
- 2 - 3 pts: Test for S. pyogenes pharyngitis, treat if +ve
- 4 - 5pts: Initiate empiric antibiotics
What is the common pathogen for bacterial pharyngitis?
Common pathogen: grp A strep
First line: use Penicillin V or Amoxicillin
Pen V allergy: Cephalexin
Amoxicillin allergy: Cefuroxime (cannot use Cephalexin as it has same R group as Amoxicillin!)
Severe allergy: Clindamycin
Common pathogen of acute rhinosinusitis
Strep pneumo, Haem Influenzae (similar to CAP)
Treat for 5-7 days
First line
- Amoxicillin Clavulanic
Penicillin allergy
- Cefuroxime
- Respiratory FQ (to cover Strep Pneumo) eg. Levofloxacin, Moxifloxacin
Symptoms of bacterial rhinosinusitis
3 Criteria to treat bacterial rhinosinusitis
Purulent discharge, facial pain / pressure, fever, nasal congestion, reduced sense of taste or smell, headache, cough, ear fullness or pressure, bad breath, dental pain
1) Symptoms persist for > 10 days without improvement
2) Severe symptoms for 3 days: 1) > 39 deg), 2) purulent nasal discharge, 3) facial pain
3) Symptoms worsen after a period of improvement
Culture directed therapy principles of Bacterial Meningitidis (if culture shows NSBL)
Neisseria meningitidis
Strep pneumo
Grp B strep
Listeria
For NSBL, use Ampicillin or Penicillin G
If Penicillin resistant or mild allergy, go back to Ceftriaxone (as used in empiric)
(special cases)
for Listeria (if penicillin allergy)
BUT Ceftriaxone cannot cover Listeria, (cos only Ampicillin can), so use Co-trimox OR Meropenem
for strep pneumo
If bug is penicillin and cephalosporin resistant, use Vancomycin + Rifampicin
Treatment for non-severe C.diff vs Severe C.diff
Non-severe: (WBC < 15 X 10^9 and SCr < 133umol/L)
First line
PO Vancomycin 125mg QDS
PO Fidaxomicin 200mg BD
2nd line
PO Metronidazole 400mg TDS
Severe C.diff
(WBC > 15 X 10^9 or SCr > 133umol/L)
- Same as non severe, but wihtout Metronidazole
Empiric coverage for treatment for Bacterial meningitidis
Which groups need to cover extra?
All use Ceftriaxone
1) Infants (1yo) until Adults > 50yo
- Need to cover Strep pneumo resistant to Ceftriaxone, hence add Vanco
2) Neonates (< 1 month old) and Adults > 50yo
- Need to cover for Listeria, hence add on Ampicillin
antibiotics that should not be used in G6PD deficiency
Cotrimox
Nitrofurantoin
Fluoroquinolones
Penicillin allergy (4 groups that share similar side chains)
Which drug is safe for all allergic reactions
If allergic to one, cannot use the rest in the grp
1) Amoxicillin, Ampicillin, cephalexin
2) Cefepime, Ceftriaxone
3) Ceftazidime, Aztreonam
4) Penicllin allergy cannot use all Penicillins, including Piptazo
Cefazolin is safe, can use in all patients with penicillin allergic reaction
Which antibiotics should be used for ESBL and Amp-C producing enterobacterales
Carbapenems
Aminoglycosides
Concentration killing drugs
Time dependent
AUC dependent
Aminoglycosides
Fluoroquinolones
Beta lactams (penicillins, Ceph, Carbapenems)
Vancomycin, tetracyclines (TDM), 50s (Clindamycin, Macrolides, Linezolid)
Lab tests that indicate infection (4 points)
High neutrophils
Increased C-reactive protein (CRP)
- acute phase reactant
- not specific to infection
Increased erythrocyte sedimentation rate (ESR)
- bone and joint infection
Increased procalcitonin
- specific to infection (more specific than CRP)
- help to determine if need to start or stop antibiotics
When do atypicals need to be covered
Which drugs are used to cover atypicals
Community acquired Pneumonia
1) Macrolides (azithromycin, clarithromycin)
2) Doxycycline
Difference in spectrum of activity between 1st gen and 2nd gen Cephs
1st gen (Cephazolin, Cephalexin) cannnot cover Strep Pneumo, 2nd gen can
