Soft Tissue Infections Flashcards by Barrett Thompson

What are the most common causes of uncomplicated (no predisposing factors) skin infections in immunocompetent people?

S. aureus and GAS

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What drugs are used in the treatment of uncomplicated non-MRSA skin infections?

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What drugs are used in the treatment of Community acquired MRSA skin infections?

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What drugs are used in the treatment of Serious MRSA skin infections?

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What drugs are used in the treatment of polymicrobial skin infections?

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What are your first line drugs in the treatment of non-MRSA skin/soft tissue infections?

Use ß-lactamase resistant Penicillins: Dicloxacillin, Nafcillin, Oxacillin

1st Gen Cephalosporins: Cephalexin, Cefazolin

**only if allergic use Lincosamides like Clindamycin or cell wall synthesis inhibitors like Vanc****

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How does a penicillin allergy reaction present?

• Urticaria, Angioedema, Bronchospasm, Anaphylaxis

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What causes the problem with 1st and 2nd generation cephalosporins also causing allergic reactions in people that are allergic to penicillin?

R1 side chain, NOT the actual ß-lactam structure

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Note: You can reduce the risk of a penicillin allergy-cephalosporin cross reaction if you select drugs that have different R1 chains. If you do this there is almost no chance of cross reaction.

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If someone was allergic to Penicillin G, which cephalosporin would you want to avoid giving this person?

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If someone was allergic to Ampicillin, what cephalosporins would you definitely not want to give them?

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If someone is allergic to amoxicillin, what cephalosporins would you definitely not want to give them?

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What resistance mechanisms do organisms use against ß-lactams?

Lack cell wall (mycobacteria, etc)
ß-lactamase, altered PBPs, efflux, and Reduced permeability

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What is the MOR to lincosamides?

Methylation or Mutation of the 50S ribosomal subunit

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What is the MOR to Vancomycin?

Gram negatives are intrinsically resistant
D-lac substitution for D-ala

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What is the primary organ toxicity to worry about with penicillins/cephalosporins?
• what do we do in cases of dysfunction in this organ?
• which penicillins are the exception? how are they excreted?

Most penicillins are eliminated in the Kidney - reduce dose because elimination will be reduced. Naficillin, Oxacillin, and Dicloxacillin are excreted via BILIARY excretion. (no dose adj. necessary)

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How is vancomycin eliminated?
• do you need to dose adjust in renal dysfunction?

Eliminated via Hepatic and Renal
• DOSE adjust in renal dysfunction

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Do you ever give Vancomycin PO for systemic infections?
• why or why not?

NO, Vancomycin has very poor bioavailability - only give PO in enterocolitis (C. diff)

Side effects of Vancomycin?

*Red Man Syndrome** (histamine-related thrombophlebitis)
*8th Cranial Nerve Damage** (hearing loss)
*Reversible Nephrotoxicity** with transient BUN elevation, hyaline and granular casts in the urine

What drugs used in the treatment of non-MRSA staph skin infections can cause interstitial nephritis?

Between Dicloxacilllin, Nafcillin, and Oxacllin:
• which can cause elevated LFTs?
• Which is given IV?

What side effect do the cephalosporins used to treat MSSA staph infections have in common with clindamycin?

Possibility of causing Stephen Johnson Sydrome

What drug used to treat MSSA skin and soft tissue infections might cause C-diff infections?

Clindamycin

Which Cephalosporin for MSSA could be given outpatient?

Cephalaxin b/c its PO and Cefazolin is IV/IM

What group of drugs should you never use in the treatment of MRSA infections whether nosocomial or community acquired?

Fluroquinolones - resistance is rapidly conferred against these drugs

What drugs used in the treatment of CA-MRSA skin infections bind to 50S ribosomal subunits? • which bind to 30S?

What are the only drugs used in the treatment of CA-MRSA that do not act on bacterial ribosomes?

TMX-SMX

What are some mechanisms of resistance toward **Linezolid**?

• Mutation of **23S rRNA** and ribosomal proteins **L3 and L4** - this ability is transferred via plasmid that carries **Cfr rRNA methyltransferase** **• Biofilms** \*\*\*Knowing resistance mechanisms here are important because Linezolid near your final line of drugs\*\*\*

If a pregnant women gets a community acquired MRSA skin infection, what drug(s) indicated for use in these infections do you definitely not want use?

Do not use TMX-SMX, or any tetracycline

What drugs used in the treatment of CA-MRSA would increase your risk of getting a sunburn?

TMX/SMX, Minocycline, Doxycycline

What are some unique side effects of Linezolid?

The most important to remember being: **myelosuppression, peripheral and optic neuropathy, lactic acidosis, serotonin syndrome**

What is the mechansim of toxicity that leads to linezolid optic nerve toxicity?

**Mitochondrial Dysfunction of the optic nerve because mitochondria use ribosomes that closely resemble bacterial ribosomes**

What are some symptoms to look for to see if a patient is getting Serotonin Syndrome? • how long does it take these symptoms to appear?

\*\*Most of these symptoms occur within 6 hours\*\* **Mental Status Changes Autonomic Hyperactivity Neuromuscular Abnormalities** **(muscle spasms etc)**

What drugs are associated with serotonin syndrome?

* SSRIs * SNRIs * TCAs * MAOIs * Some Opiates * Isoniazid * Buspirone * Triptans * Amphetimines * Procarbazine * Bromocriptine * Psychotropic Drugs HERBALS • St. Johns Wort • Ginseng

What are your treament options for serious MRSA infections? • why would you prefer one over the other?

Treatment options for Serious MRSA are: • **Vancomycin** - bactericidal, good emprical tx. • **Linezolid** - can stop toxin production, but not bactericidal • **Daptomycin** - bactericidal, maybe good for VRSA

What is the appropriate treatment for a polymicrobial bacterial skin and soft tissue infection?

Add a **MRSA drug** (Vanc., Dapto, or Linezolid) to a broad-spectrum parenteral antibiotic like: **• Pip/Tazo • Impi/Cilastin • Meropenem • Ceftaroline**

**Ceftaroline fosamil** • MOA • Common adverse effects • Elmination

MOA This is a Vth generation Cephalosporin so if inhibits PBPs needed to make cell walls - **BROAD SPECTRUM** Adverse Effects: • Rash, N/D/constipation, **Hypokalemia** • C. diff, **ALT/AST elevation, and Hemolytic Anemia** may also be seen Elimination: • **Primarily Renal Elimination**

What does Cilastin do?

• Prevents metabolism of Imipenem by brush border dihydropeptidase to reno-toxic products

What is the MOA of Daptomycin?

What are some side effects to watch out for with Daptomycin? • How can you monitor this?

Monitor the patient's CK to see how much muscle breakdown is occurring

What side effects are associated with Pip/Tazo?

What side effects are typically associated with the carbapenems?

Note that CNS toxicity (siezures) are only really associated with Imipenem

Remember to monitor BUN and Creatinine in patients taking beta lactams other than Naficillin, Oxacillin, or D-cillin and dose adjust for kidney dysfunction