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Infectious Disease > Sulfonamides > Flashcards

Sulfonamides Flashcards

1
Q

What is a sulfonamide group?

A

SO2-N

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2
Q

What is a “sulfa” drug?

A

Contains a sulfonamide group

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3
Q

Describe bacterial folate synthesis

A
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4
Q

Sulfonamide antibiotics MOA

A

Competively Inhibit the enzyme Dihydropteroate Synthase preventing PABA from becoming Dihydropteroic acid and thereby inhibiting DNA synthesis

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5
Q

Trimethoprim MOA

A

Inhibits Dihydrofolate Reductase thereby preventing dihydrofolic acid from forming tetrahydrofolate thus inhibiting DNA synthesis

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6
Q

Pyrimethamine MOA

A

Inhibits Dihydrofolate Reductase thereby preventing dihydrofolic acid from forming tetrahydrofolate thus inhibiting DNA synthesis

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7
Q

List of Sulfonamide antibiotics

A
  • Sulfamethoxazole (SMX)
  • Sulfisoxazole
  • Sulfadiazine
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8
Q

What are Sulfonamide antibiotics?

A

mimics of PABA that Competitively inhibit dihydropteroate synthase

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9
Q

Mechanisms of Resistance to sulfonamide antibiotics

A
  • increase amount of PABA inside the cell
  • Altered dihydropteroate synthase
  • Decreased uptake of the drug
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10
Q

Another drug that competes with PABA for dihydropteroate Synthase that is not a sulfonamide?

A

Dapsone

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11
Q

What is Dapsone?

A

NOT a sulfonamide

Competitively inhibits dihydropteroate synthase

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12
Q

Clinical uses of Dapsone?

A
  • Mycobacterium leprae (leprosy)
  • Pneumocystitis jiroveci
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13
Q

Clinical applications of sulfonamide antibiotics

A

Sulfamethoxazole is usually given with trimethoprim

  • TMP-SMX (Bactrim)
    • Sequential block of THF synthesis

Sulfadiazine

  • Silver-sulfadiazine (cream) for burns

Sulfadiazine and Pyrimethamine

  • sequential block of THF synthesis
    • used in toxoplasmosis (HIV)
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14
Q

Adverse effects of sulfonamide antibiotics

A
  • Hypersensitivity reaction 3% of pts
  • reactions linked to
    • Arylamine (NH2) at N4 position
    • Nitrogen ring attached to N1 nitrogen
    • Only sulfonamide antibiotics contain both features
  • Hypersensitivity reactions include like PCN
    • anaphylaxis
    • delayed maculopapular rash
    • serum sickness
    • interstitial nephritis
    • Stevens-Johnson Syndrome or TEN
  • Photosensitivity
    • drug interaction with UV light
    • Caused by many drugs such as tetracycline, sulfonamides and amiodarone
  • Hemolysis in G6PD deficient patients
    • sulfonamides are oxidants so act as a trigger
    • Dapsone is also a trigger
  • binds to albumin and displace other bound substances such as bilirubin or warfarin
    • Kernicterus in infants (sulfonamides increase free bilirubin levels) unconjugated bilirubin is neurotoxic (basal ganglia, brainstem nuclei)
      • Permanent neurologic impairment
      • movement disorders (chorea, tremor)
      • Hearing loss
      • Limited gaze
    • Raise warfarin levels so the INR may raise if Sulfonamides are taken, also because GI bacteria may be disrupted (any antibiotic can do this) from making Vitamin K2 leading to increased INR.
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15
Q

Which antibiotics inhibit dihydrofolate reductase?

A
  • Trimethoprim
  • Pyrimethamine
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16
Q

Trimethoprim and Pyrimethamine chemical structure

A

similar to dihydrofolate

17
Q

Trimethoprim and Pyrimethamine adverse effects

A

Trimethoprim and Pyrimethamine retain some activty against human DHF reductase so this inhibits the folate pathway in rapidly dividing human cells

  • Bone marrow suppression
    • pancytopenia, megaloblastic anemia, leukopenia, decreased platelets

Can be alleviated with Leucovorin (folinic acid)

  • converted to THF
  • does not require dihydrofolate reductase
  • “Leucovorin rescue”
18
Q

TMP-SMX bacterial effect

A

Each by themself are bacteriostatic but the Combination is bactericidal

19
Q

TMP-SMX coverage

A
  • Covers many Gpos and Gneg
  • Does NOT cover Pseudomonas
  • Does NOT cover B. fragilis (and most anaerobes)
  • Covers some fungi and parasites
20
Q

Common uses of TMP-SMX

A
  • Urinary tract infections
  • Pneumocystitis pneumonia in HIV (treatment/prophylaxis)
21
Q

TMP-SMX contraindications

A
  • Pregnancy
    • Risk of Kernicterus w/ sulfonamides antibiotics
    • also trimethoprim can disrupt human folic acid metabolism
22
Q

PCP AKA

A

Pneumocystis Pneumonia

23
Q

What is Pneumocystis jirovecii?

A

an opportunitic fungal infection which occurs in end stage HIV/AIDS

24
Q

Treatment of choice for Pneumocystis jirovecii

25
Q

Considerations of TMP-SMX in Pneumocystis jirovecii infection

A

hypersensitivity reactions are 6-25x more likely in HIV

alternative therapies may be needed

26
Q

Alternative therapies for Pneumocystis jirovecii

A
  • Dapsone
  • Pentamidine
  • Atovaquone (malaria drug)

Infectious Disease (82 decks)

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