Antibiotics 1 Study Questions

For what organisms are natural penicillins the preferred therapy?

Streptococcis pyogenes, Treponema Pallidum(syphilis),

What staphylococci do the anti-staphylococcal (AKA Penicillinase resistant PCNS) penicillins not cover?

Methicillin-resistant Staphylococcus aureus (MRSA)

What is unique about the anti-staphylococcal penicillins in terms of excretion and dosing adjustments?

Short half lives mean they need frequent dosing, however they are are hepatically excreted so they DONT require renal dosing adjustments

What are the differences between ampicillin and amoxicillin?

Amoxicillin is the oral equivalent of ampicillin

AMP is the drug of choice for vanco susceptible enterococci

Unlike ampicillin, Amox is not for meningitis

How does the spectrum change when adding a beta-lactamase inhibitor? E.g. amoxicillin to amox-clav?

Added gram - coverage: Gram- anaerobes, H. Influenzae, M. Cat (Moraxella catarrhalis), enterobacterales

Increased gram+ coverage: MSSA, VGS

What are the anti-pseudomonal beta-lactams?

Pip/tazo

Ceftazidime

Cefepime

Imipenem, Meropenem

Aztreonam

What is the spectrum trend with cephalosporin generations? What are the exceptions?

First gen: Strong Gram+ coverage

Second gen: added Gram - coverage

Third gen: most active against gram-

(except ceftriaxone, it does both)

(Ceftazidime is active against pseudomonas)

Fourth gen: Good activity against both Gram- and Gram +

Fifth gen: More Gram+, plus MRSA

What 3rd generation cephalosporins are active against Penicillin-resistant Streptococci?

ceftriaxone,cefotaxime

What are the gaps in cefepime coverage? What toxicity is associated with cefepime?

NO MRSA

NO Enterococci

NO anaerobes

Neurotoxicity Risk

What makes ceftaroline unique as a beta-lactam?

MRSA Activity

What are the gaps in carbapenem coverage? How is ertapenem different?

No MRSA

No H influenza, meningitis, gonorrhea, syphilis, Listeria

Ertapenem does not cover pseudomonas and is only once daily

What toxicity is associated with carbapenems?

CNS, Seizures, increases metabolism of VPA

What is the spectrum for aztreonam? In what patients would you consider using it?

Good: Pseudomonas, most GNRs Poor: Gram+, anaerobes Consider using in pts who have hypersensitivity to other Beta lactams

What are the general adverse reactions to beta-lactams?

Hypersensitivity

Nephrotoxicity

CNS toxicity

GI

Thrombocytopenia

What is the difference in coverage between the cephamycins (cefoxitin, cefotetan) and the other second generation cephalosporins?

They are active against gram- anaerobes (tin tan)

What patients are at higher risk of severe beta-lactam reaction?

Adults

History of PCN Rxns

Parenteral administration

Recent B lactam exposure

Persistence B lactam specific IgE antibody response

What beta-lactams interact with H2 antagonists, PPIs, and antacids? Why and how do you manage it?

Oral cephalosporin prodrugs cefpodoxime, cefuroxime and cefditoren interact with H2RAs and PPIs Cefaclor, Cefdinir, Cefpodxime and Cefditoren interact with antacids Avoid or separate admin by 2 hours *This happens bc some cephalosporins are prodrugs or require acidic conditions for solubility and absorption in the small intestine. PPIs , H2 antagonists, and antacids, increase stomach pH, leading to impaired dissolution and absorption of these cephalosporins.

What beta-lactams are most affected by probenecid? What is the interaction?

Probenecid inhibits renal section causing increase concentration, it is recommended to avoid or half the dose of the antibiotic

Most: Amoxicillin, ampicillin, cefoxitin, cefaclor, cefdinir