Fluoroquinolones

Question 1

Fluoroquinolones (FQs)

Answer 1

Broad spectrum CIDAL agents used mostly for G- and some G+ organisms

Question 2

What is the mechanism of fluoroquinolones?

Answer 2

G-: Inhibits DNA gyrase which messes up replication

G+: Inhibits topoisomerase IV which affects the separating of replicated DNA strands into daughter cells

Question 3

Ciprofloxacin

Answer 3

• 2nd gen FQ
• Best for G- activity
• Lowers clearance of theophylline → increased theophylline levels → toxicity
• Drug interactions: increased levels of methadone and trizanide → respiratory depression, sedation, hypotension and hallucinations

Question 4

Norfloxacin

Answer 4

• 2nd gen FQ
• LEAST ACTIVE
• Low systemic levels
• Used for UTIs only

Question 5

Ofloxacin

Answer 5

• 2nd gen FQ
• Oral is generic
• Ophthalmic and otic also available

Question 6

Gatifloxacin

Answer 6

• 3rd gen FQ
• Ophthalmic solution only
• Only 3rd gen that is NOT respiratory

Question 7

Gemifloxacin

Answer 7

• 3rd gen respiratory FQ

Question 8

Levofloxacin

Answer 8

• 3rd gen respiratory FQ
• Active isomer of ofloxacin
• Avoid if cardiac conduction anomalies (can lead to prolonged Q-T in elderly → Torsades de pointes)
• Risk of acute hepatitis and fatal events

Question 9

Moxifloxacin

Answer 9

• 3rd gen respiratory FQ
• Metabolized mainly by liver
• Caution if hepatic disease present
• Can prolong Q-T interval in healthy patients

Question 10

Besifloxacin

Answer 10

• 4th gen FQ

* Used for bacterial conjunctivitis

Question 11

General side effects of all FQs

Answer 11

1. Phototoxicity
2. Arthropathy
3. Tendon rupture
4. Can alter blood sugar in diabetics
5. CNS stimulation
6. Nausea, vomiting, diarrhea
7. Diplopia

Question 12

What should you not mix FQs with?

Answer 12

Antacids and iron supplements (can decrease absorption of antibiotic)

Question 13

Why are 3rd generations FQs known as respiratory FQs?

Answer 13

Because they are more active against S. pneumoniae than 2nd gen FQs.

Question 14

What is the newest side effect of FQs reported?

Answer 14

Peripheral neuropathy (may occur anytime during therapy and may be permanent!)

Question 15

What is the bug and inflammation that causes diarrhea after taking an FQ?

Answer 15

Pseudomembranous colitis caused by C. difficile
• Forms sports and then grows w/o competition
• Secretes 2 exotoxins and fors a pseudomembrane placque

Question 16

What antibiotic is used to treat Pseudomembranous colitis caused by C. difficile?

Answer 16

Fidaxomicin
• A narrow spectrum CIDAL antibiotic vs C. diff
• Inhibits RNA polymerase
• It and metabolites have significant post antibiotic effect