Antibiotics Flashcards
Penicillin V
Beta-lactam, penicillin
Acid-resistant (can take orally)
Sensitive to penicillinases
Limited spectrum (YES G+, G- cocci, NO G- rods)
Similar: Penicillin VK (+ potassium, more soluble)
Penicillin G
“Original” penicillin
Beta-lactam
Acid labile - can’t take orally (only IV, IM)
Sensitive to penicillinases
Limited spectrum (G+ and G- cocci - NOT enteric G- rods)
- Neisseria meningititis
- Treponema pallidum (syphilis)
Ampicillin
Beta-lactam (penicillin)
Sensitive to penicillinase
Acid stable
Broader spectrum - G- enteric, most G+
Amoxicillin
Beta-lactam (penicillin)
Sensitive to penicillinase
Acid stable
Broader spectrum - G- enteric, most G+
Tricarcillin
Beta-lactam (carboxypenicillin) Sensitive to penicillinase Acid stable Extended spectrum - effective against G- enteric (including Pseudomonas aeruginosa) - less action against G+
Piperacillin
Beta-lactam (ureidopenicillin) Sensitive to penicillinase Acid stable Extended spectrum - most effective against Pseudomonas aeruginosa, anaerobic, G- - less effective against G+
Methicillin
Beta-lactam (penicillin) Resistant to penicillinase Acid labile Altered spectrum - targets Staphylococcus aureus (MRSA = resistant) - not effective vs G-
Oxacillin
Beta-lactam (penicillin) Resistant to penicillinase Acid stable (vs methicillin) Altered spectrum - targets Staphylococcus aureus - not effective vs G-
Similar: naficillin, dicloxacillin
Penicillins
Beta-lactam ring + thiazolidine ring + R group
Bacteriocidal but only if cell is growing
Inhibit cell wall synthesis -> lysis
PBP = transpeptidase = penicillin binding protein
Resistance = beta-lactamase (hydrolyzes ring)
- often acquired on plasmid
Cephalosporins
Sim to penicillins - beta lactam - bacteriocidal when dividing Dihydrothiazide ring -> More resistant to penicillinases, acid Can use if penicillin allergy
Broad spectrum - most Gram +, some Gram -
Cefazolin
1st gen cephalosporin (beta lactam)
Most Gram +
Some Gram -
Not pseudomonas aeruginosa
Cefuroximide
2nd generation cephalosporin (beta lactam)
More Gram -
Fewer Gram +
Not pseudomonas aeruginosa
Ceftriaxone
3rd generation cephalosporin (beta lactam)
Penetrates blood-brain barrier
Most Gram -
Ceftazimide
3rd generation cephalosporin (beta lactam)
Broad spectrum Gram -
Effective against Pseudomonas aeruginosa
Aztreonam
Mono-bactam (sim to beta-lactam but resistant to breakdown)
Aerobic Gram -
includes Pseudomonas aeruginosa
Not Gram + or anaerobic
Imipenem
Carbapenem (beta lactam)
Broadest spectrum vs Gram -
MRSA variable
Susceptible to renal dipeptidases
Clavulonic acid
Beta-lactamase inhibitor
+ amoxicillin = Augmentin
Sulbactam
Beta-lactamase inhibitor
+ ampicillin = Unasyn
Vancomycin
Glycopeptide - inhibits cell wall synthesis
Blocks transfer of D-Ala-D-Ala
Toxic
Only Gram + (too big for outer membrane porins)
Enterococcus or staphylococcus (ex MRSA)
Oral for C diff
Resistance is possible
Cycloserine
D-Ala analog -> blocks cell wall synthesis
Toxic
Tuberculosis
Bacitracin
Blocks phosphatase in murein (cell wall) synthesis
Toxic -> topical only
Only Gram +
Polymyxin B
Disrupts membrane permeability (-> cidal even without growth)
Toxic -> topical
Gram - enterics (including Pseudomonas)
Aminoglycosides
Distort 30S subunit -> cidal
Require aerobic conditions, some metabolic activity for entry into cell
Toxic
Streptomycin
Initial aminoglycoside
Aerobic conditions, metabolic activity, imperfections ->
Entry -> distorts 30S -> misreading -> funny proteins ->
Disrupts membrane -> cidal
Lots of resistance
Toxic
Used for TB
Gentamycin
Aminoglycoside
Multiple inhibitions to 30S
(less resistance than streptomycin)
Toxic (nerve, renal) - not generally used
Tetracyclines
also includes doxycicline and monocycline
Block tRNA-30S binding -> static
Broad spectrum
- mycoplasma, rickettsia, chlamydia
- GI microbiome changes
Teratogenic, yellow teeth in kids
Erythromycin
Macrolide
Blocks 50S chain elongation -> static
Most Gram +
Mycoplasma
Chlamydia
Azythromycin
Similar to erythromycin (macrolide, blocks chain elongation)
High concentrations at infection site dt macrophages
Chloramphenicol
Blocks chain elongation -> static
Aplastic anemia - not commonly used
Anaerobes
- Bacteriodes fragilis
Clindamycin
Blocks peptidyl transfer -> static
Some Gram +
Anaerobes
Streptogramins
New class Binds to 50S -> static
Dalfopristin + quinopristin = Synergin (work synergistically)
MRSA, VRE, etc
Oxazolidinones
aka linezolid, Zyvox
Blocks tRNA transfer -> static
Gram +
New -> VRE, MRSA, etc
- some resistance already
Mupirocin
Block isoleucine aminoacyl transferase ->
- static at low, cidal at high
Topical vs MRSA (surgeons)
Impetigo (Staph aureus, Strep pyogenes)
Quinolones
aka Ciprofloxacin, Moxifloxacin
Inhibits gyrase -> DNA synthesis -> cidal
Inhibits bone growth -> teratogen, kids
Gram + cocci Enteric Gram - bacilli - includes Pseudomonas aeruginosa Anthrax prophylaxis No longer MRSA (resistance)
Metronidazole
Requires anaerobic conditions -> ferredoxin reduces/activates
Fragments DNA -> cidal
Bacteroides
Protozoal - trichomaniasis, amebiasis
Rifampin
Inhibits RNA synthesis -> cidal
Broad spectrum
Tuberculosis (with isoniazid)
Saliva prophylaxis (Neisseria meningititis)
Ethambutol
Unknown mechanism
Static
Tuberculosis
Isoniazid
Blocks InhA enzyme -> mycolic acid -> cell wall -> cidal
Tuberculosis
Pyrazinamide
Unknown mechanism
Activated by amidase -> cidal
Tuberculosis
Reasons to give two drugs
Synergism Susceptibility pattern Decreased resistance Lower dose of toxic drug Polymicrobial infection
Mechanisms of resistance
Enzymatic degradation
(Beta-lactam, aminoglycoside, chloramphenicol, erythromycin)
Decreased permeability
(penicillins, chloramphenicol, aminoglycoside)
Active efflux (tetracycline)
Altered targets
(vancomycin, erythromycin, streptomycin, methycillin, sulfonamide, trimethoprim)
Alternative pathway (trimethoprim)
Sulfonamide
Analog of PABA -> blocks THF production -> static
Wide range
Protozoa
UTI
Trimethoprim
Blocks DHF reductase -> THF synthesis -> static
(same enzyme in humans but much higher affinity)
UTI (Bactrim = combo with sulfa)
Antibiotic sensitivity methods
Minimum inhibitory concentration
- Determine via tube dilution -> no growth
Minimum bactericidal concentration
- requires tube -> plate -> no growth after removed
Disc diffusion - simple, simultaneous, doesn’t determine MBC
Betalactamase production - nitrocefin = chromogenic
Ideal antibiotic properties
Kill bacteria, no toxicity or allergy to host
Should kill faster than it is inhibited
Should kill faster than resistance develops
Should reach bacteria (abcess, brain, inside cells)
Ideal does NOT exist…
Major classes of antibiotics
Antimetabolites - sulfonamides, trimethoprim, isoniazid
Inhibitors of cell wall synthesis - beta-lactams, glycopeptides
Membrane permeability - polymyxins
Inhibitors of protein synthesis - aminoglysides, macrolides, tetracycline, chloramphenicol
Inhibitors of nucleic acid synthesis - quinolone, rifampin
