Penicillins Flashcards
Penicillins (PCNs)
- CIDAL agents used against organisms that synthesize peptidoglycan
- Ineffective against fungi and protozoa
- Thiazolidine + β-lactam rings form the PCN nucleus & are required for activity
What is the mechanism of penicillins?
Irreversibly inhibit transpeptidase (helps create cross links in peptidoglycan cell wall) which leads to inhibition of cell wall synthesis and lysis
PCN G
- β-lactam
- Activity Against Gram+ Organisms, Gram- Cocci and Non-Beta-Lactamase Producing Anaerobes
- Bactericidal
- Poor Oral Bioavailability
- Caution: can enter CNS if meninges inflamed
What are the 3 forms of PCN G?
- Aqueous - solution for IM/IV
- Procaine - suspension for IM; sometimes combined with benzathine
- Benzathine - suspension for IM; longest acting
What is the main mechanism of PCN resistance?
β-lactamase enzyes, a.k.a. PCNases, that destroy the β-lactam ring thus inactivating the antibiotic
PCN V
- β-lactam
- Acid stable form for oral use
- Food interferes w/absorption (give 1 hr before/after meal)
Aminopenicillins
- Extended spectrum PCNs
- More G- coverage
- Still susceptible to PCNases
Which form of PCN G is most likely to cause an allergic reaction and why?
Procaine because it’s an ester and for some reason people tend to be more allergic to esters
Penicillinase (β-lactamase) -Resistant PCNs
- Used only if the microbe does not respond to PCN G or V
* Excreted by biliary and renal secretion (good for people w/hepatic or renal failure; other organ can pick up slack)
Dicloxacillin
- Oral
* Penicillinase (β-lactamase) -Resistant PCN
Oxacillin
- Parenteral
* Penicillinase (β-lactamase) -Resistant PCN
Nafcillin
- Parenteral
* Penicillinase (β-lactamase) -Resistant PCN
Methicillin Resistant S. aureus (MRSA)
• S. aureus strains that are resistant to all Penicillinase Resistant PCNs
Ampicillin
• Oral or IV
• Available w/Sulbactam (β-lactamase inhibitor) as Unasyn
• Unasyn is DOC for peritonitis due to Bacteroides fragilis
AminoPCN
Amoxicillin
• Only given orally
• Available w/Clavulanate (β-lactamase inhibitor) as Augmentin
• Used for otitis media and prophylaxis before dental work for high risk pts
AminoPCN
Antipseudomonas PCNs
Active vs some Pseudomonas & some resistant Proteus but still susceptible to PCNases
Ticarcillin + Clavulanate
• Parenteral
• Only available together
Antipsuedomonas PCN
Piperacillin + Tazobactam
• Parenteral
• Tazobactam is a β-lactamase inhibitor
• Piperacillin available alone or w/Tazobactam
Antipsuedomonas PCN
General side effects of all PCNs
- Hypersensitivity rxns
- Diarrhea (see: Fidaxomicin and C. diff)
- Superinfection
- Increased risk of seizures if penetrate BBB
- Decreased renal function increases risk - as drug accumulates, may enter CNS
- Jarisch-Herxheimer Rxn
Jarisch-Herxheimer Rxn
- Not an allergic reaction
- Occurs in 70-90% of pts w/secondary syphilis
- Resolves spontaneously
- Causes flu-like Sx
- Tx: ASA (aspirin)
