Uworld: RxPrep Infectious Disease I

Common Pathogens:

CNS/Menigitis

Streptococcus pneumoniae

Neisseria meningitidis

Haemophilus influenzae

Group B Streptococcus/E.coli (young)

Listeria (young/old)

Common Pathogens:

Upper Respiratory

Streptococcus pyogenes

Streptococcus pneumoniae

Haemophilus influenezae

Moraxella catarrhalis

Common Pathogens:

Heart/Endocarditis

Staphylococcus aureus including MRSA

Staphylococcus epidermis

Streptococci

Enterococci

Common Pathogens:

Skin/Soft Tissue

Staphylococcus aureus

Staphylococcus epidermis

Streptococcus pyogenes

Aerobic/anaerobic GNRs (in diabetes)

Common Pathogens:

Bone/Joint

Staphylococcus aureus

Staphylococcus epidermis

Streptococci

GNRs

Common Pathogens:

Mouth

Mouth flora (Peptostreptococcus)

Anaerobic GNRs (Prevotella, others)

Viridians group streptococci

Common Pathogens:

Lower Respiratory (Community)

Streptococcus pneumoniae

Haemophilus influenezae

Atypical: Legionella, Mycoplasma, Chlamydophila

Common Pathogens:

Lower Respiratory (Hospital)

Staphylococcus aureus including MRSA

Streptococcus pneumoniae

Pseudomonas aeruginosa

Acinetobacter baumannii

Enteric GNRs (including ESBL +, MDR)

Gram-positive:

organisms have a thick cell wall and stain dark purple or blue from the crystal violet stain

Gram-negative:

organisms have a thin cell wall and take up the safranin counterstain, resulting in a pink color

Atypical

organisms have an altered or absent cell wall and do not stain well (identified by other means)

Gram (+) Clusters:

Staphylococcus spp. including MRSA and MSSA

Gram (+) Pairs & Chains:

Streptococcus pneumoniae (diplococci)

Streptococcus spp. (including S. pyogenes)

Enterococcus spp. (including VRE)

Gram (+) Rods:

Listeria monoctyogenes

Corynebacterium spp.

Gram (+) Anaerobes:

Peptostreptococcus

Cutibacterium acnes

Clostridiodes difficile

Clostridium spp.

Organisms that don’t stain well:

Atypicals: Chlamydophila, Legionella. and Mycoplasma

Mycobacterium tuberculosis

Gram (-) Cocci:

Neisseria spp.

Gram (-) Anaerobes:

Bacteroides fragillis

Prevotella spp.

Gram (-) Coccobacilli:

Acinetobacter baumannii

Bordetella pertussis

Moraxella catarrhalis

Gram (-) Rods that colonize the gut:

Proteus mirabilis

Escherichia coli

Klebsiella spp.

Serratia spp.

Enterobacter cloacae

Citrobacter spp.

Gram (-) Rods that are curved or spiral:

H.pylori, Campylibacter spp., Treponema spp., Borrelia spp., Leptospira spp.

Gram (-) Rods that don’t colonize the gut:

Pseudomonas aeruginosa

Haemophilus influenzae

Providencia spp.

Common Resistant Pathogens:

Kill Each And Every Strong Pathogen

Klebsiella pneumoniae (ESBL, CRE)

Escherichia coli (ESBL, CRE)

Acinetobacter baumannii

Enterococcus faecalis, Enterococcus faecium (VRE)

Staphylococcus aureus (MRSA)

Pseudomonas aeruginosa

Subcategories of Beta-Lactams

Penicillin

Cephalosporins

Carbapenems

Monobactam (Aztreonam)

Beta-Lactams MOA:

inhibit bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs)

Spectrum of Activity:

Natural PCNs

active against gram (+):

streptococci and enterococci

Spectrum of Activity:

Antistaphylococcal PCNs

covers streptococci and MSSA

Spectrum of Activity:

Aminopenicillins

covers streptococci, enterococci, and gram-positive anaerobes (mouth flora) plus the gram-negative bacteria Moraxella catarrhalis as well as Haemophilus, Neisseria, Proteus, and E. Coli (HNPE)

Ampicillin has actives against which gram (+) rods?

Listeria

Spectrum of Activity:

Aminopenicillins + Beta-lactamase inhibitors

active against MSSA, more resistant strains of gram (-) bacteria (HNPEK), and gram (-) anaerobes (B.fragilis)

Spectrum of Activity:

Extended-spectrum PCNs + Beta-Lactamase inhibitor

same coverage as aminopenicillin/beta-lactamase inhibitor plus activity against gram (-) bacteria including Pseudomonas and the AmpC hyperproducers Klebsiella aerogenes, Citrobacter freundii, and Enterobacter cloacae (KCE)

List all the natural PCNs and their specific route of administration

Penicillin V Potassium : PO

Penicillin G Aqueous (Pfizerpen): IV

Penicillin G Benzathine (Bicillin L-A): IM

Penicillin G Benzathine and Penicillin G Procaine (Bicillin C-R): IM

Which PCN carries a BBW, and what is the warning?

Penicillin G Benzathine (Bicillin L-A) not for IV use; inadvertent IV administration can cause can cause cardio-respiratory arrest and death

The 3 contraindications listed for PCNs

1. Type 1 hypersensitivity reaction to another PCN or beta-lactam antibiotic

2. Augmentin and Unasyn: history of cholestatic jaundice or hepatic dysfunction associated with previous use

3. Severe renal impairment (CrCl <30 mL/min): do not use Augmentin ER or the 875 mg strength

PCNs SE:

Seizures (with accumulation when not dose-adjusted in renal dysfunction)

Gi upset

diarrhea

renal failure

elevated LFTs

rash (SJS/TEN)

allergic reaction/anaphylaxis

hemolytic anemia (identified with a positive Coombs test)

PCNs monitoring:

Renal monitoring

Antistaph PCN class and their routes:

Dicloxacillin (PO)

Nafcillin (IV)

Oxacillin (IV)

Antistaph primary clinical uses and renal dosing rules

Preferred for MSSA soft tissue, bone and joint, endocarditis, and bloodstream infections.

Require no renal dose adjustments. 

What local tissue risk is associated with IV nafcillin, and how is it treated?  

Nafcillin is a vesicant; if extravasation occurs, use cold packs and hyaluronidase injections.  

Why is PO ampicillin rarely used, and what is preferred when switching from IV ampicillin?

Ampicillin PO has poor bioavailability; amoxicillin is preferred for IV-to-PO step-down

Why is Augmentin ES-600 preferred for pediatric acute otitis media? 3) What is the preferred diluent for IV ampicillin and Unasyn?

Augmentin ES-600 suspension has a lower clavulanate concentration, resulting in a lower risk of diarrhea

How can Piperacillin/Tazobactam (Zosyn) be administered?

Intermittent (e.g., Q6H or Q8H) or prolonged/extended infusions (e.g., Q8H infused over 4 hours)

What is Pivmecillinam (Pivya) approved for?  

Pivmecillinam (Pivya) is an oral penicillin approved for acute uncomplicated cystitis

How do penicillins affect warfarin, and which two penicillins have the opposite effect?  

Most beta-lactams enhance warfarin's anticoagulant effect (by inhibiting vitamin K-dependent clotting factors)

Nafcillin and dicloxacillin are CYP enzyme inducers and inhibit warfarin's anticoagulant effect.  

How do penicillins interact with probenecid and methotrexate?  

Probenecid: Increases beta-lactam levels by interfering with renal excretion (sometimes used intentionally in severe infections).  

 Methotrexate: Penicillins increase serum concentrations of methotrexate. 

What are the two major class effects of penicillins, and what is the clinical exception to avoiding them in a beta-lactam allergy?  

Allergy Rule: All penicillins should be avoided in patients with a beta-lactam allergy. Exceptions: Treatment of syphilis during pregnancy or in patients with poor adherence/follow-up (desensitize and treat with penicillin G benzathine).  

 Neurotoxicity: All penicillins increase the risk of seizures if accumulation occurs (e.g., failure to dose-adjust in renal dysfunction).  

What is the primary clinical indication for Penicillin VK?  

A first-line treatment for pharyngitis ("strep throat"). 

What are the 3 key clinical uses and specific dosing regimens for Amoxicillin?  

1. Acute otitis media (pediatric dose: 80–90 mg/kg/day) and bacterial sinusitis.  

2. Drug of choice for infective endocarditis prophylaxis before dental procedures (2 grams PO x 1, 30–60 minutes before procedure).  

3. Used in H. pylori treatment regimens.  

What are the common uses, pediatric otitis media dose, and formulation pearl for Amoxicillin/Clavulanate?  

Common Uses: Acute otitis media (pediatric dose: 90 mg/kg/day) and bacterial sinusitis.  

 Dosing Pearl: Use the lowest dose of clavulanate to decrease diarrhea

What is the spectrum of activity and renal dosing rule for Dicloxacillin (oral) and Nafcillin / Oxacillin (parenteral)? 

Spectrum: Covers MSSA (not MRSA).  

 Renal Dosing: No renal dose adjustments needed.

What is the primary indication, dosing regimen, and critical route warning for Penicillin G Benzathine?  

Indication & Dose: Drug of choice for syphilis (2.4 million units IM x 1).  

 Route Warning: Not for IV use (can be fatal).  

What is the unique spectrum pearl and infusion optimization strategy for Piperacillin/Tazobactam? 

Spectrum: Only penicillin active against Pseudomonas.  

 Infusion Pearl: Extended infusions (4 hours) can be used to maximize T > MIC

1st Gen Cephalosporins

1st Generation: Cephalexin, Cefadroxil (PO); Cefazolin (IV)

2nd Gen Cephalosporins

2nd Generation: Cefuroxime (PO, IV); Cefotetan, Cefoxitin (IV); Cefaclor, Cefprozil (PO)

3rd Gen Cephalosporins

3rd Gen Group 1: Cefdinir, Cefpodoxime, Cefixime/Suprax (PO); Ceftriaxone, Cefotaxime (IV, IM — Note: Cefotaxime is no longer manufactured in the U.S.; available via importation if needed).  

 3rd Gen Group 2: Ceftazidime/Tazicef (IV).  

4th Gen Cephalosporins

 4th Gen: Cefepime (IV).  

5th Gen Cephalosporins

5th Gen: Ceftaroline fosamil/Teflaro, Ceftobiprole medocaril/Zevtera (IV).  

Cephalosporin/Beta-Lactamase Inhibitor

Ceftazidime/Avibactam/Avycaz, Ceftolozane/Tazobactam/Zerbaxa (IV).  

 Siderophore Cephalosporin: Cefiderocol/Fetroja (IV).  

What are the two neonatal contraindications for ceftriaxone, and what biliary side effect can it cause?  

Hyperbilirubinemic neonates: Displaces bilirubin, which can cause kernicterus.  

 Neonates receiving IV calcium: Concurrent use with calcium-containing IV products is contraindicated (even at different times of the day).  

 Side Effect: Biliary sludging (forms insoluble precipitates with bilirubin and calcium in the bile). 

What is the cross-reactivity rate with penicillin allergy, and when must cephalosporins be avoided?

Cross-reactivity with penicillin allergy is < 1–2% (lower risk with later-generation cephalosporins); do not use in patients with a type 1 hypersensitivity to penicillin (swelling, angioedema, anaphylaxis).  

Which cephalosporin causes a disulfiram-like reaction with alcohol?  

Cefotetan can cause a disulfiram-like reaction with alcohol ingestion.  

What is the primary monitoring parameter for cephalosporins, and what are the major side effects? 

Monitoring: Renal function.  

Side Effects: Seizures (with accumulation when not dose-adjusted in renal dysfunction), GI upset, diarrhea, acute interstitial nephritis, myelosuppression (with prolonged use), increased LFTs, drug fever, rash (including SJS/TEN), allergic reactions/anaphylaxis, hemolytic anemia (positive Coombs test), and ceftriaxone biliary sludging.  

What are the key renal dosing and CNS pearls for ceftriaxone?

Ceftriaxone: Requires no renal dose adjustments; achieves CNS penetration at high doses (e.g., 2 g Q12H) when meninges are inflamed.  

Which oral cephalosporin is NOT available as a suspension, and which comes as a chewable tablet? 

All oral cephalosporins except cefuroxime are available as oral suspensions; cefixime is available as a chewable tablet.  

How must IV calcium and ceftriaxone be managed in adults?

Avoid simultaneous administration in the same line (forms insoluble precipitates); may be given at different times of day if the IV line is flushed with a compatible fluid between products.  

Which 3 oral cephalosporins have decreased bioavailability with acid-suppressing drugs, and how are they managed?  

Cefuroxime, cefpodoxime, and cefdinir should be separated by 2 hours from short-acting antacids, and H2RAs and PPIs should be avoided.