Antimicrobials Flashcards
What are the agent(s) of the folate anti-metabolites class?
Trimethoprim-sulfamethoxazole (sulfonamides and trimethoprim rarely used separately)
What is the mechanism of action of folate anti-metabolites?
Prevent production of tetrahydrofolate for synthesis of purines and thymidine
- Sulfonamide inhibits dihydropteroate synthetase
- Trimethoprim inhibits dihydrofolate reductase
What is the spectrum of activity for folate anti-metabolites?
Traditionally used for Gram negatives
Some Gram positive activity including S. aureus
Some protozoa and fungi
What are common adverse events of folate anti-metabolites?
Common: nausea, vomiting, headache, rash
Rare: Stevens-Johnson syndrome, drug interactions
What are the major clinical uses of folate anti-metabolites?
UTI and respiratory infections
Increasing use for S. aureus
What are the agent(s) of the quinolones (and fluoroquinolones)?
Ciprofloxacin, Moxifloxacin
What is the mechanism of action of the quinolones?
Form complex with DNA and topoisomerase II or IV, preventing the topoisomerase from fixing the DNA double strand breaks
What are the mechanisms of resistance of folate anti-metabolites?
Genetic mutation
Plasmid (containing alternate dhfr allele in the case of trimethoprim)
What are the mechanisms of resistance of quinolones?
Mutations in target enzyme (topoisomerase)
Efflux pumps
What are common adverse effects of quinolones?
Common: GI intolerance, headache, nervousness
Rare:
Seizures
May prolong QT interval in patients taking other medications that can prolong QT
Tendon rupture
What is the spectrum of activity of quinolones?
Active against most Gram negatives and “atypicals” (Mycoplasma, Chlamydia, Legionella, Mycobacteria)
Moxifloxacin is also active against Gram positive Strep and anaerobes
What are the clinical uses of quinolones?
GI infections
Ciprofloxacin - UTIs
Moxifloxacin - Pneumonia, mycobacterial infections, polymicrobial infections due to anaerobic activity
What is the spectrum of activity of Nitrofurantoin?
Gram-pos and Gram-neg uropathogens (Staph, Strep, Enterococcus, Klebsiella)
What are the clinical uses of Nitrofurantoin?
Only used for UTI
What agent(s) are in the Rifamycins class?
Rifampin
Rifabutin
Rifaximin
What is the mechanism of action of rifamycins?
Binds beta subunit of RNA polymerase and blocks transcription
What is unique about the pharmacology/kinetics of rifamycins?
Metabolized by P450 3A4
- Rafampin: potent induced, can increase metabolism of other drugs
- Rifabutin: levels can rise in presence of P450 inhibitors
- Rifaximin: not absorbed, only taken PO
What are common adverse events of rifamycins?
Turns secretions orange!
GI intolerance
Hematologic or hepatic toxicity
What is the spectrum of activity of rifamycins?
Very broad, includes Gram pos, Gram neg, anaerobic and mycobacterial
What are the clinical uses of rifamycins?
Prophylaxis (for Neisseria)
Used in combination with other antimicrobials, i.e. in the treatment of Mycobacterial TB infection
Rifaximin: just treats GI infections since poorly absorbed
What is the spectrum of activity of Fidaxomicin?
Only Gram-positive bacteria
But also has less dramatic effect on fecal microbiome than other agents
What are the clinical uses of Fidaxomicin?
C. diff colitis
What antimicrobials fall under the category of Beta-lactam agents?
Penicillins
Cephalosporins
Carbapenems
Monobactams
What are mechanisms of resistance of Penicillins?
Beta-lactamase
Modified Penicillin-binding proteins (e.g. e.g. PBP2A encoded by the mecA gene which results in methicillin-resistant Staphylococcus aureus (MRSA), with a decreased affinity for β-lactam antibiotics)
What are the common adverse events of Penicillins?
Hypersensitivity reactions (rashes, serum sickness) At high concentrations: seizures
What are the classes of Penicillins?
Penicillin G (and V)
Semi-synthetic penicillins
Aminopenicillins
“Antipseudomonal” penicillins
What is the spectrum of activity of Penicillin G?
Gram positive cocci and anaerobes
Gram negative cocci
Spirochetes (syphilis)
What are the clinical uses of Penicillin G?
Infections caused by most Streptococci (if susceptible)
Gram positive anaerobic infections (dental abscesses, bites)
Syphilis
What agents are in the class of semi-synthetic penicillins and are they IV or PO?
Nafcillin - IV
Dicloxacillin - PO
What is the spectrum of activity of semi-synthetic penicillins?
NO Gram negatives
ONLY Gram positive cocci and anaerobes
What are the clinical uses of semi-synthetic penicillins?
Infections due to methicillin-SUSCEPTIBLE S. aureus (MSSA)
What agents fall in the class of aminopenicillins and are they IV or PO?
Ampicillin - IV
Amoxicillin - PO
What is the spectrum of activity of aminopenicillins?
Gram positive cocci and anaerobes
Some Gram neg bacilli
What are the clinical uses of aminopenicillins?
Community-acquired HEENT and upper respiratory infections
Community-acquired UTIs
What agents fall in the class of “antipseudomonal” penicillins?
Piperacillin
What is the spectrum of activity of Piperacillin?
Includes highly-resistant Gram-neg bacilli like Pseudomonas
What are the clinical uses of Piperacillin?
NONE ON ITS OWN. Only used in combination with tazobactam as a beta-lactamase inhibitor
What is the mechanism of action of beta-lactamase inhibitors?
Bind and hydrolyze beta-lactamases while beta-lactams remain intact and exert effect
What agents fall under the class of beta-lactamase inhibitors?
Ampicillin-sulbactam
Amoxicillin-clavulanic
Piperacillin-tazobactam
What is the spectrum of activity of beta-lactamase inhibitors?
Very broad. Beta lactam combined with inhibitor covers:
- Gram pos like S. aureus (but not MRSA)
- Beta-lactamase producing Gram neg and anaerobes
- Piperacillin-tazobactam also covers Pseudomonas!
What are the clinical uses of beta-lactamase inhibitors?
Polymicrobial infections or resistant infections
What is the mechanism of action of cephalosporins?
Beta-lactam
How do beta-lactam agents work?
Covalently bind transpeptidases involved in forming the peptide cross-links in the peptidoglycan, creating a weakened cell wall.
Autolysins will lyse cell.
What are the first generation cephalosporins?
Cefazolin
Cephalexin
What are the common adverse events of cephalosporins?
Minimal side effects
Hypersensitivity
Possible cross-reactivity with penicillin allergy
What is the spectrum of activity of first generation cephalosporins?
Gram positive Strep and Staph
Some Gram negative bacilli
What are the clinical uses of first generation cephalosporins?
Cefazolin - antimicrobial prophylaxis during surgery
Cephalexin - oral cephalosporin, usually skin and soft tissue infections from Strep and Staph (not MRSA)
What are the second generation cephalosporins?
Cefoxitin
What is the spectrum of activity of second generation cephalosporins?
Gram pos Strep and Staph
Excellent activity against Gram neg anaerobes
Increased activity against Gram neg bacilli
What are the clinical uses of second generation cephalosporins?
Treat intraabdominal infections or prophylaxis in intraabdominal surgery
What are the third generation cephalosporins?
Ceftriaxone, Ceftrazidime
What is the spectrum of activity of third generation cephalosporins?
Gram-pos Strep and Staph
Excellent activity against Gram neg cocci and bacilli (high degree of penetration into CSF)
What are the clinical uses of third generation cephalosporins?
Cefriaxone - meningitis, endocarditis and osteomyelitis, community-acquired pneumonia
Ceftazidime - covers Pseudomonas!
What are the mechanisms of resistance to cephalosporins?
More resistant to beta-lactamases (not much effect)
Intrinsic resistance (mostly enterococci and Pseudomonas)
Altered membrane permeability - Pseudomonas
Altered PBPs