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Pharmacology (Topic C) > 11. Chloramphenicol. Polymyxins. Antifolate drugs > Flashcards

11. Chloramphenicol. Polymyxins. Antifolate drugs Flashcards

1
Q

What is the MOA of Chloramphenicol?

A

Binds 50s ribosomal unit.

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2
Q

What spectrum does Chloramphenicol cover?

A

Gram+ and Gram- anaerobes and aerobes:

  1. Rickettsiae, Spirochetes
  2. Staph, Strep, Salmonella, Shigella, E. coli, B. fragilis
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3
Q

What are the side effects of Chloramphenicol?

A
  1. GI symptoms: Nausea, Vomitting and Diarrhea.
  2. Bone marrow suppression: 2 types
    • Dose-related, reversible - in 100% pts with dose > 20 g. 1st RBCS, then WBCs + platelets
    • Irreversible, dose-independent: aplastic anemia in 1:20,000 pts, tx with marrow transplantation.
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4
Q

What are the indications of Chloramphenicol?

A

Few due to high toxicity

  1. Severe Rickettsia in children under 8 - above 8 y/o tetracyclines are used (since tetracyclines can cause problems in growing bone)
  2. Meningitis by pneumococci, meningococci or H. flu - if there is cephalosporin allergy
  3. Brain abscess - with resistance to metronidazole
  4. (Eye infections - topically as a cream; but many other good options, so only when they are ineffective)
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5
Q

What interactions can occur with Chloramphenicol?

A
  1. Inhibits CYP enzymes → altered drug effects.
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6
Q

What is the mechanism of resistance to Chloramphenicol?

A

Resistance is due to decreased permeability or by deacetylation via chloramphenicol acetyltransferases.

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7
Q

How is Chloramphenicol metabolized?

A

Degraded by glucuronide conjugation in the liver. Immature enzymes in newborns → accumulation in skin → grey baby syndrome (flaccid muscles, hypothermia, vomiting, shock + collapse).

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8
Q

Where in the world is Chloramphenicol used?

A
  1. It is rarely used in developed countries.
  2. SE are more commonly seen in developing countries due to the fact that it’s cheap.
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9
Q

How are the absorption and distribution properties of Chloramphenicol?

A

Good oral absorption + distribution (enters CNS, abscesses, IC space, eye, pleural + peritoneal cavity)

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10
Q

What is the MOA of Polymixins?

A

Colistin also known as polymyxin E. Polymixin E is a cationic detergent → membrane disruption.

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11
Q

What are the indications of Polymixins?

A
  1. Severe multi-resistant infections (multi-resistant Acinetobacter “MACI”, etc.). UTI, cystitis (as local wash).
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12
Q

What are the side effects of Polymixins?

A
  1. Highly toxic → nephro- and peripheral neurotoxic (no CNS entry).
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13
Q

List the Antifolate drugs.

A
  1. Trimethoprim + Sulfamethoxazole (combo = cotrimoxazole)
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14
Q

What is the MOA of antifolate drugs?

A
  1. SMX is PABA analog → inhibits dihydropteroate synthase.
  2. TMP inhibits DHFR.
  3. Together have a bactericidal effect.
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15
Q

What spectrum does antifolate drugs cover?

A

Gram + cocci and Gram - rods:

  1. Staph, Strep (but S. pyogenes + Enterococci are resistant)
  2. E. coli, Klebsiella, H. flu, Proteus, Salmonella, Shigella
  3. More rare infections: Nocardia, Brucella, Aeromonas, P. jiroveci, Yersinia
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16
Q

What is the route of administration of antifolate drugs?

A

Given orally every 8-12 hrs.

17
Q

What are the side effects of antifolate drugs?

A

Mostly from SMO:

  1. Skin reactions: including SJS + photosensitivity
  2. Allergy: Fever, urticaria, rash
  3. Hematologic Rxns: pancytopenia or megaloblastic anemia; contraindicated in G6PD deficiency → hemolytic anemia.
  4. Renal effects: type IV RTA, crystalluria and interstitial nephritis.
  5. Long term → ↓ folic acid → give leucovorin (folic acid)
  6. (Teratogen if used in 1st trimester → neural tube defects; kernicterus if used in last trimester)
  7. (Displaces warfarin from albumin → increased bleeding risk)
  8. (Inhibits CYP450)
18
Q

What are the indications for antifolate drugs?

A
  1. Respiratory infections: sinusitis, otitis, acute exacerbation of chronic bronchitis (not tonsillopharyngitis b/c ↓ S. pyo effect)
  2. UTI: 1st line treatment for simple UTI, not pyelonephritis.
  3. Prostatitis
  4. Recurrent Cystitis: 4-6 wks treatment
  5. Traveller’s Diarrhea: Salmonella etc.
  6. P. jiroveci: 1st line (2nd clindamycin or atovaquone) + other rare infections above.
19
Q

What spectrum does Polymyxin E/Colistin cover?

A

Covers a narrow spectrum, only Gram - aerobe (GI rods), but Proteus, Serratia are resistant. Pseudomonas + Acinetobacter are highly susceptible.

20
Q

How are anti-folate drugs metabolized and excreted?

A
  1. Metabolized in liver
  2. Excreted in urine (↓ dose in kidney impairment)
21
Q

What are the side effects of Polymyxin E/Colistin?

A
  1. Highly toxic → nephro- and peripheral neurotoxic (no CNS entry)

Pharmacology (Topic C) (20 decks)

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