Penicillins

Question 1

Penicillins (PCNs)

Answer 1

• 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

Question 2

What is the mechanism of penicillins?

Answer 2

Irreversibly inhibit transpeptidase (helps create cross links in peptidoglycan cell wall) which leads to inhibition of cell wall synthesis and lysis

Question 3

PCN G

Answer 3

• 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

Question 4

What are the 3 forms of PCN G?

Answer 4

1. Aqueous - solution for IM/IV
2. Procaine - suspension for IM; sometimes combined with benzathine
3. Benzathine - suspension for IM; longest acting

Question 5

What is the main mechanism of PCN resistance?

Answer 5

β-lactamase enzyes, a.k.a. PCNases, that destroy the β-lactam ring thus inactivating the antibiotic

Question 6

PCN V

Answer 6

• β-lactam
• Acid stable form for oral use
• Food interferes w/absorption (give 1 hr before/after meal)

Question 7

Aminopenicillins

Answer 7

• Extended spectrum PCNs
• More G- coverage
• Still susceptible to PCNases

Question 8

Which form of PCN G is most likely to cause an allergic reaction and why?

Answer 8

Procaine because it’s an ester and for some reason people tend to be more allergic to esters

Question 9

Penicillinase (β-lactamase) -Resistant PCNs

Answer 9

• 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)

Question 10

Dicloxacillin

Answer 10

• Oral

* Penicillinase (β-lactamase) -Resistant PCN

Question 11

Oxacillin

Answer 11

• Parenteral

* Penicillinase (β-lactamase) -Resistant PCN

Question 12

Nafcillin

Answer 12

• Parenteral

* Penicillinase (β-lactamase) -Resistant PCN

Question 13

Methicillin Resistant S. aureus (MRSA)

Answer 13

• S. aureus strains that are resistant to all Penicillinase Resistant PCNs

Question 14

Ampicillin

Answer 14

• Oral or IV
• Available w/Sulbactam (β-lactamase inhibitor) as Unasyn
• Unasyn is DOC for peritonitis due to Bacteroides fragilis
AminoPCN

Question 15

Amoxicillin

Answer 15

• 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

Question 16

Antipseudomonas PCNs

Answer 16

Active vs some Pseudomonas & some resistant Proteus but still susceptible to PCNases

Question 17

Ticarcillin + Clavulanate

Answer 17

• Parenteral
• Only available together
Antipsuedomonas PCN

Question 18

Piperacillin + Tazobactam

Answer 18

• Parenteral
• Tazobactam is a β-lactamase inhibitor
• Piperacillin available alone or w/Tazobactam
Antipsuedomonas PCN

Question 19

General side effects of all PCNs

Answer 19

1. Hypersensitivity rxns
2. Diarrhea (see: Fidaxomicin and C. diff)
3. Superinfection
4. Increased risk of seizures if penetrate BBB
5. Decreased renal function increases risk - as drug accumulates, may enter CNS
6. Jarisch-Herxheimer Rxn

Question 20

Jarisch-Herxheimer Rxn

Answer 20

• Not an allergic reaction
• Occurs in 70-90% of pts w/secondary syphilis
• Resolves spontaneously
• Causes flu-like Sx
• Tx: ASA (aspirin)