ID I Flashcards
Gram positive
thick cell wall, dark purple or bluish from crystal violet stain
Staphylococci (gram-positive organisms occurring in cluster) can be differentiated with a coagulase (enzyme) test. Which is coagulase positive?
Staphylococcus aureus
Gram negative
thin cell wall, pick or reddish from the safranin counterstain
What is minimum inhibitory concentration (MIC)?
minimum concentration of each antibiotic that inhibits bacterial growth
REMEMBER: MICs are specific to each antibiotic & organism -> cannot be compared among different antibiotics
example of synergism
Aminoglycosides & beta-lactams can be used together synergistically to treat certain invasive gram-positive infections (e.g., infective endocarditis
COMMON RESISTANT PATHOGENS
Remember: Kill Each And Every Strong Pathogen
Klebsiella pneumoniae (ESBL, CRE)
Escherichia coli (ESBL, CRE)
Acinetobacter baumannii
Enterococcus faecalis, Enterococcus faecium (VRE)
Staphylococcus aureus (MRSA)
Pseudomonas aeruginosa
Risk of C. diff is highest with…
broad-spectrum penicillins and cephalosporins, quinolones, carbapenems, & clindamycin (which has a BBW)
Generally, cell wall & cell membrane inhibitors, DNA/RNA inhibitors, and aminoglycosides are __________ (kill bacteria or inhibit bacterial growth?).
bactericidal (kill bacteria)
Generally, most protein & folic acid synthesis inhibitors are __________.
bacteriostatic (inhibit growth)
Folic acid synthesis inhibitors
- Sulfonamides
- Trimethoprim*
- Dapsone
*often combined with sulfamethoxazole to overcome resistance
Protein synthesis inhibitors
- Aminoglycosides
- Macrolides
- Tetracyclines
- Clindamycin
- Linezolid, tedizolid
- Quinupristin/dalfopristin
DNA/RNA inhibitors
- Quinolones (DNA gyrase, topoisomerase IV)
- Metronidazole, tinidazole
- Rifampin
Cell membrane inhibitors
- Polymyxins
- Daptomycin
- Telavancin
- Oritavancin
Protein synthesis inhibitors
- Aminoglycosides
- Macrolides
- Tetracyclines
- Clindamycin
- Linezolid, tedizolid
- Quinupristin/dalfopristin
Cell wall inhibitors
- Beta-lactams (penicillins, cephalosporins, carbapenems)
- Monobactams (aztreonam)
- Vancomycin, dalbavancin, telavancin, oritavancin
Hydrophilic agents
- Beta-lactams
- Aminoglycosides
- Vancomycin
- Daptomycin
- Polymyxins
Features of hydrophilic agents
1) Small volume of distribution -> less tissue penetration
2) Mostly renally eliminated -> drug accumulation & side effects (e.g., nephrotoxicity) can occur if not dose adjusted
3) Low intracellular concentrations -> not active against atypical (intracellular pathogens)
4) Poor-moderate bioavailability -> IV:PO ratio not 1:1
Lipophilic agents
- Quinolones
- Macrolides
- Rifampin
- Linezolid
- Tetracyclines
Features of lipophilic agents
1) Large Vd -> better tissue penetration
2) Mostly hepatically metabolized -> potential for hepatotoxicity & DDIs
3) Achieve intracellular concentrations -> active against atypical (intracellular) pathogens
4) Excellent bioavailability -> IV:PO ratio often 1:1
Drugs with concentration-dependent killing can be dosed ______ frequently and in _______ doses. These antibiotics include…
Drugs with concentration-dependent killing can be dosed less frequently and in higher doses. These antibiotics include:
- aminoglycosides
- quinolones
- daptomycin
Drugs with time-dependent killing can be dosed ______ frequently. These antibiotics include…
Drugs with time-dependent killing can be dosed more frequently or each dose can be administered for a longer duration to maximize the time above MIC.
- Examples include extending the infusion time of beta-lactams or administering drug as continuous infusion
These antibiotics include…
- beta-lactams (penicillins, cephalosporins, carbapenem)
AUC:MIC (exposure-dependent) drugs
Vancomycin, macrolides, tetracyclines, polymyxins
MOA of penicillins
inhibit bacterial cell wall synthesis by binding to PBPs -> prevent final step of peptidoglycan synthesis in bacterial cell walls
BOXED WARNING of penicillin G benzathine (Bicillin L-A)
NOT for IV use -> can cause cardiorespiratory arrest & death
Severe renal impairment (CrCl <30) -> do not use…
extended-release forms of amoxicillin & amoxicillin/clavulanate (Augmentin XR), or the 875 mg strength of Augmentin
side effects of penicillins
- Seizures (with accumulation) when not correctly dose adjusted in renal dysfunction
- GI upset, diarrhea
- Rash (including SJS/TEN/allergic rxns/anaphylaxis
- Hemolytic anemia (identified with positive Coombs test)
- Renal failure
- Myelosuppression with prolonged use
- increased LFTs
Which penicillins do NOT require renal dose adjustments?
Antistaphylococcal penicillins (dicloxacillin, naficillin, oxacillin)
What is special to know about naficillin specifically?
Naficillin is a vesicant -> administration through central line preferred. If extravasation occurs, use cold packs & hyaluronidase injections
What medication can increase the levels of beta-lactams by interfering with renal excretion? (but combination sometimes used intentionally in severe infections to increase antibiotic levels)
Probenecid
