Antibiotics

Question 1

What some things that are considered when dosing antibiotics prophylactically?

Answer 1

• The antimicrobial level in the blood should exceed MIC by 2-8x to provide prophylaxis against infection
• **Lots of services use lots of Cefazolin → Clinda, vanco, gentamicin are typical backups if allergy present
• T1/2 are basis of re-dosing
• Presence of renal failure should decrease dosage of cephalosporins and macrolide

Question 2

What antibiotic classes are considered beta-lactam antibiotics? Why?

Answer 2

PCNs, Cephalosporins, Monobactams, Carbapenems

They are broad spectrum antibiotics that contain a beta-lactam ring in the structure

Question 3

1. What class of antibiotic is cefazolin?
2. What bacteria is this active against?
3. Should dose be decreased in renal failure? Why?

Answer 3

1. First generation cephalosporin
2. Gram +
3. Yes, because it is excreted largely unaltered by the kidneys

Question 4

Cephalosporins

1. MOA
2. What are the cross-reactions/allergies/toxicities that come with them?

Answer 4

1. Bactericidal via interruption of cell wall synthesis
   - More resistant to beta-lactamases
   - Resistance is due to inability to penetrate the site of action
2. 5-10% MAY have cross-reactivity with PCNs and/or carbapenems. → if no suitable alternatives forces use in these patients because not too high
   - 5-10% MAY have cross-reactivity with PCNs and/or carbapenems. → if no suitable alternatives forces use in these patients because not too high
   - Low incidence of toxicity and nephrotoxicity

Question 5

Monobactams

1. Specific drug
2. What bacteria is this active against?

Answer 5

1. Aztreonam

2. Gram -

Question 6

Why would we use a carbapenem?

Answer 6

Broader spectrum than other beta-lactams → useful for multi-drug resistant infections
Less affected by mechanisms of antibiotic resistance

Question 7

Clindamycin

1. What are problems with this?
2. What bacteria is this active against?
3. Should dose be decreased in renal failure? Why?

Answer 7

1. Can cause pseudomembranous colitis and produces junctional effects at the NMJ (high doses can result in long lasting blockade)
2. Anaerobes
3. No, renal failure only slightly prolongs T1/2 elimination

Question 8

Macrolides

1. Examples
2. MOA
3. Use
4. Should dose be decreased in renal failure? Why?
5. Delivery

Answer 8

1. Vanco, erythromycin, azithromycin
2. Imapirs cell wall synthesis of Gm + microbes
3. Drug of choice for MRSA
4. Yes, 1/2 is 6 hours but up to 9 days with renal failure → adjust dose
5. IV Vanco (10-15mg/kg) given slowly over 60 minutes → faster administration results in large histamine release = Red Man, severe hypotension and possible cardiac arrest
   - Sustained plasma concentration for 12 hours → rarely re-dose in the OR

Question 9

Fluroquinolones

1. Examples
2. Use

Answer 9

1. Cipro and moxiflaxacin
2. highly effective for urinary and genital tract infections (prostatitis and GI infections); upper and lower respiratory infections as well as soft tissue, bone and joint infections

Question 10

Chlorhexidine

1. MOA
2. Coverage

Answer 10

1. disrupts the cell membranes of bacteria
2. effective against Gm - and Gm + → persists on skin to provide continuous coverage. (2% is more effective than providing-iodine)

Question 11

Iodine

1. Percentages related to time
2. When is iodine effective?

Answer 11

1. • 1% kills 90% of bacteria in 90 seconds
     - 5% kills 90% in 60 seconds
     - >7% = burns
2. Must be DRY to be effective