186: Systemic and Topical Antibiotics Flashcards
(107 cards)
What are the indications for penicillin therapy in treating skin and soft tissue infections (SSTIs)?
Penicillin therapy is indicated for:
- Syphilis and nonvenereal treponematoses
- Empiric treatment of mild or moderate nonpurulent SSTIs
- Infections caused by Streptococcus spp., Clostridium spp., spirochetes, Pasteurella multocida, Eikenella corrodens, and Erysipelothrix rhusiopathiae
What are the common side effects and precautions associated with penicillin use?
Common side effects and precautions include:
- Hypersensitivity reactions ranging from mild to severe
- Penicillin is a leading cause of drug-induced anaphylaxis, accounting for approximately 1% to 10% of all cases
- 5% to 10% of the general population reports an allergy to penicillin, which is likely overreported
- Skin prick testing can detect Type I hypersensitivity, followed by intradermal testing if negative
- Desensitization is recommended for patients with a positive skin test if a B-lactam is necessary
What is the mechanism of action of B-lactam antibiotics, including penicillins?
B-lactam antibiotics, including penicillins, work by:
- Binding to specific penicillin-binding proteins
- Inhibiting cell wall peptidoglycan synthesis
- Inactivating an inhibitor of autolytic enzymes present on bacterial cell walls
What steps should be taken to confirm penicillin allergy in a patient requiring treatment for a severe purulent SSTI?
Skin prick testing followed by intradermal testing if negative. If the tests are negative, a challenge dose of oral penicillin under observation may be administered. If positive, desensitization or alternative antibiotics like vancomycin may be used.
What are the characteristics of extended-spectrum penicillins and their activity against Pseudomonas spp.?
Extended-spectrum penicillins, such as carboxypenicillins (carbenicillin, ticarcillin) and ureidopenicillins (piperacillin), have a broad spectrum and susceptibility to B-lactamase. They exhibit some activity against Pseudomonas spp. and Proteus spp. Ureidopenicillins are derived from ampicillin and have greater activity against Gram-negative organisms, including Pseudomonas.
What is the significance of antistaphylococcal penicillins in treating infections?
Antistaphylococcal penicillins, such as oxacillin, dicloxacillin, and nafcillin, are B-lactamase resistant and are effective against S. aureus. They are the drug of choice (DOC) for methicillin-sensitive S. aureus SSTIs but have no activity against enterococci or Gram-negative organisms. They are important for empiric therapeutic use in treating certain infections.
How should oral penicillins be administered to ensure proper absorption?
Most oral penicillins should be taken at least 1 hour before or after meals to avoid food binding. However, amoxicillin is unaffected by food. Other penicillins like penicillin G, nafcillin, carbenicillin, ticarcillin, and piperacillin are unstable at low pH and poorly absorbed, thus requiring careful administration.
What are the metabolic and excretion characteristics of penicillins?
Penicillins are typically excreted renally, with free penicillin being excreted in the urine. Nafcillin, oxacillin, and ureidopenicillins are excreted via the hepatobiliary system. They are generally poorly absorbed and can be degraded by colonic bacteria. Additionally, they do not typically cross the blood-brain barrier, although meningitis can enhance permeability.
What is the pregnancy category of penicillins and their safety during breastfeeding?
Penicillins are classified as Pregnancy Category B, indicating they are excreted in breast milk in low quantities and are considered safe during breastfeeding.
What are the indications for using first-generation cephalosporins in treating SSTIs?
First-generation cephalosporins, such as Cephalexin and Cefazolin, are indicated for uncomplicated SSTIs caused by Staphylococcus aureus and Streptococcus pyogenes. They are effective for mild or moderate nonpurulent SSTIs (cellulitis) where community-acquired MRSA is not suspected.
What is the expanded Gram-negative activity of second-generation cephalosporins compared to first-generation cephalosporins?
Second-generation cephalosporins, such as Cefprozil and Cefoxitin, have expanded Gram-negative activity over first-generation agents, particularly against H. influenzae and Moraxella catarrhalis.
What are the side effects and precautions associated with first and second-generation cephalosporins?
First and second-generation cephalosporins cross-react with penicillin in approximately 10% of penicillin-allergic patients. It is important to assess for penicillin allergy before prescribing these medications.
How do third-generation cephalosporins differ in their effectiveness against Gram-positive organisms compared to earlier generations?
Third-generation cephalosporins, such as Cefdinir and Ceftriaxone, have expanded Gram-negative activity but are less effective against Gram-positive organisms compared to first and second-generation cephalosporins.
What is the significance of cross-reactivity between cephalosporins and penicillin?
Cross-reactivity between cephalosporins and penicillin is significant as it can lead to allergic reactions in patients with a penicillin allergy. First and second-generation cephalosporins cross-react in 10% of cases, while third-generation cephalosporins cross-react in 2% to 3% of cases.
Which cephalosporins are safer options for a patient with a history of penicillin allergy?
Cefdinir, cefpodoxime, and cefuroxime are safer options because they lack side chain similarity to penicillin, ampicillin, or amoxicillin.
Which cephalosporin generation is least likely to cross-react in a patient with a history of penicillin allergy?
3rd-generation cephalosporins are least likely to cross-react, with a cross-reactivity rate of 2% to 3%.
DELETE
B-lactam antibiotics inhibit bacterial cell wall synthesis by blocking peptidoglycan incorporation.
What are the indications for Ceftaroline in the treatment of SSTIs?
Ceftaroline is indicated for complicated SSTIs, including those caused by MRSA, and is an option for empiric therapy for severe purulent SSTIs.
How does the spectrum of activity of 4th generation cephalosporins compare to 3rd generation cephalosporins?
4th generation cephalosporins, such as Cefepime, have increased activity against Gram (+) organisms compared to 3rd generation cephalosporins and are also active against Gram (-) organisms like Pseudomonas and Enterobacteriaceae.
What is the significance of the dihydrothiazine ring in B-lactam antibiotics?
The dihydrothiazine ring in B-lactam antibiotics provides resistance to some, but not all, B-lactamases, affecting their efficacy against resistant bacteria.
What are the dietary considerations for taking esterified cephalosporins like cefuroxime and cefpodoxime?
Esterified cephalosporins require food to extend mucosal contact time and allow enzymatic cleavage; medications that lower gastric pH can reduce their absorption.
What drug is used for a severe SSTI caused by MRSA, and what is its spectrum of activity?
Ceftaroline is used. It has a broad spectrum of activity against Gram-positive organisms, including MRSA, and some Gram-negative organisms.
What generation and specific drug should be used for a severe SSTI caused by Pseudomonas aeruginosa?
A 4th-generation cephalosporin like cefepime should be used due to its activity against Pseudomonas aeruginosa.
What is the mechanism of action of tetracyclines in bacterial treatment?
Tetracyclines inhibit bacterial protein synthesis by binding to the 30S ribosomal subunit and blocking transfer RNA binding to the messenger RNA-ribosome complex.