PCNs and Cephalosporins Flashcards
What was the first natural antibiotic?
penicillin G
The cell envelope of this type of bacteria:
Gram stain: Red/Pink
3 layer envelope
Gram (-)
The cell envelope of this type of bacteria:
Gram stain: Blue/Purple
2 layer envelope
Gram (+)
What are some common Gram (+) bacteria? (3)
Staphylococcus aureus (MRSA, VRSA)
Enterococcus faecalis (VRE)
Clostridium species
Gram (+) bacteria can be found on the skin.
What are some Gram (-) bacteria? (3)
Salmonella species
Escherichia coli
Pseudomonas aeruginosa
What type of antibiotic is a “great benefit to medicine and molecular biology”?
Natural antibiotics
What beta-lactams are bacteriocidal?
All
What are common mechanisms of drug resistance?
Mutations in target proteins
Enzymes that inactivate agents (e.g. Beta-lactamases, many others)
Spontaneous changes in membrane permeability
What antibiotics target cell wall synthesis? (4)
PCNs
cephalosporins
monobactams
carbapenems
What is the mechanism of action of beta-lactams? (3)
bind to penicillin-binding proteins (PBPs)
inhibit transpeptidases
stimulate autolysins which results in cell lysis
What are the mechanisms of beta-lactam resistance? (4)
- b-lactamases
- reduced pcn binding proteins affinity for b-lactam
- changes in outer memberane permeability
- acquired tolerace
Overall, b-lactams are considerably toxic. True or false?
False
Low toxicity
What are the adverse reactions to b-lactams? (4)
anaphylaxis
hypersensitivity
wheezing
urticaria
How are PCNs excreted?
renal tubular cells
Do PCNs enter the CNS?
No, except when the meninges is inflamed.
What is the approximate half life of an oral PCN?
0.5-1 hour
What are 2 natural penicillins?
penicillin G and V
Note: Reduced usage due to widespread resistance.
What is the spectrum of activity for natural PCNs?
Gram + only
Natural PCNs such as G, V, and benzathine are still a drug of choice for (5)
S. pneumoniae (G)
Syphilis (G-Benz)
N. meningitidis (G)
Minor childhood infections, esp.otitis (V)
Strep throat (G-Benz)
What are 2 semi-synthetic penicillinase resistant drugs?
Nafcillin
Dicloxacillin
What category of b-lactam is good for:
Gram + streptococci
Limited due to MRSA
Good CNS penetration w/ meninges inflammation
Semi-synthetics: Nafcillin, Docloxacillin
What are semi-synthetic, extended spectrum b-lactams?(3)
Ampicillin/sulbactam (Unasyn)
- Amoxicillin/clavulanate (Augmentin)
- Piperacillin/tazobactam (Zosyn)
For semi-synthetic, extended spectrum antibiotics, what is the activity spectrum for:
Gram +
Gram -
extended Gram +
some Gram -
What are new, synthetic PCN-like b-lactams?
Carbapenems
What is a type of carbapenem?
Imipenem/cilastatin (Primaxin)
When and why is Primaxin administered?
Used only during superinfections
It is the broadest spectrum b-lactam.
Why is cilastatin combined in Primaxin, the synthetic PCN?
Inhibits the renal enzyme that immediately degrades the antibiotic.
What is a semi-synthetic mono-bactam?
Aztreonam (Azactam)
What is the activity spectrum of semi-synthetic monobactams?
Inhibits PBP’s of Gram(-) only.
Not active against Gram+ strains.
What class of b-lactam:
- Not affected by b-lactamases
- No b-lactam allergy reaction
- Gram (-) only
- Nosocomial (hospital acquired) infections
- Used in combination with Gram+ agents for extended spectrum
monobactam
Drug is aztreonam (Azactam)
Note: Prescribed for pts will allergic reactions with b-lactams.
What PCN:
Used in hospital acquired urinary tract and pneumonia
Especially used for pts allergic to PCN
Gram - only
monobactams
Aztreonam (Azactam)
What PCN:
Not as effective as antibiotics alone
Used in combo with other PCNs
Blocks actions of PCNases
semi-synthetics, extended spectum
Unasyn
Augmentin
Zosyn
What are characteristics of cephalosporins? (4)
Close relative of PCNs (very similar)
Compound is a natural product of molds, like PCNs
Rarely used as a drug of choice
Prophylaxis in surgery
Mechanism of action and drug resistance is similar to PCNs. True or false?
True
Cephalosporin half life is shorter than PCNs. True or false?
False, longer than.
___% of pts w/ PCN reactions also show
hypersensitivity to cephalosporins.
5%
3rd generation cephalosporins have good CNS penetration, but it is worse than PCNs. True or false?
False, good penetration.
What are first generation cephalosporins? (2)
Cephazolin (Ancef)
Cephalexin (Keflex)
What is the activity spectrum of first generation cephalosporins?
Gram+ and SOME Gram-
What are the clinical uses of 1st generation cephalosporins (Ancef, Keflex)?
Surgical prophylaxis
UTI
ENT infections due to E. coli
What are second generation cephalosporins? (2)
Cefuroxime (Zinacef)
Cefuroxime axitel (Ceftin)What is the activity spectrum of second generation cephalosporins?
Gram+ and extended Gram-
What are the clinical uses of 2nd generation cephalosporins? (3)
H. influenza
E. coli
Surgical prophylaxis
What are third generation cephalosporins?
Ceftriaxone
Ceftazidime
What is the activity spectrum of 3rd generation cephalosporins?
Gram +
Extended Gram -
CNS penetration
Long half life
What are the clinical uses of 3rd generation cephalosporins?
meningitis
sepsis of unknown origin
pneumonias
What is a 4th generation cephalosporin?
Cefepime (Maxiprime)
What is the activity spectrum of a 4th generation cephalosporin?
Very broad of both Grams
Aerobic
What is the most useful cephalosporin for nosocomial infection that are highly resistant?
Cefeprime (Maxiprime)
What is the molecular target for b-lactams?
cell wall synthesis
