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Pharmacology (3) > CH4 | Folate Antagonists > Flashcards

CH4 | Folate Antagonists Flashcards

1
Q

What is folic acid essential for?

A

A coenzyme essential for the synthesis of RNA, DNA, and certain amino acids.

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2
Q

What happens in the absence of folate?

A

Cells cannot grow or divide.

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3
Q

What is the critical folate derivative?

A

Tetrahydrofolic acid.

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4
Q

How do humans obtain folate?

A

Through dietary intake folate.

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5
Q

How do bacteria synthesize folate?

A

Through de novo folate synthesis.

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6
Q

What do sulfonamides do?

A

Inhibit de novo synthesis of folate.

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7
Q

What is the function of trimethoprim?

A

Prevents microorganisms from converting dihydrofolic acid to tetrahydrofolic acid.

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8
Q

What is the effect of the combination of sulfonamides and trimethoprim?

A

They have a synergistic effect.

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9
Q

What are examples of sulfonamides?

A

Sulfamethoxazole, sulfadiazine, sulfasalazine.

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10
Q

What is the mechanism of action (MOA) of sulfonamides?

A

They are synthetic analogs of PABA that compete with PABA and are bacteriostatic.

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11
Q

What type of bacteria do sulfonamides have activity against?

A

Both Gram-positive and Gram-negative bacteria.

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12
Q

How do some bacteria exhibit natural resistance to sulfonamides?

A

By obtaining folate from their environment.

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13
Q

What are the acquired mechanisms of resistance to sulfonamides?

A

Altered dihydropteroate synthetase, enhanced production of PABA, and decreased cellular permeability.

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14
Q

How are sulfonamides absorbed?

A

Well absorbed after oral administration.

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15
Q

Is there an intravenous form of sulfonamides available?

A

Yes, IV forms are available.

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16
Q

Why is sulfasalazine used?

A

It is not absorbed and is used for chronic inflammatory bowel diseases, acting locally.

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17
Q

What are silver sulfadiazine and mafenide used for?

A

They are used topically for burn-associated sepsis to prevent colonization of bacteria.

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18
Q

How do sulfonamides distribute in the body?

A

They bind to serum albumin and are distributed widely in body tissues.

19
Q

Do sulfonamides penetrate the central nervous system?

A

Yes, they penetrate well into the CSF and placental barrier.

20
Q

How are sulfonamides metabolized in the liver?

A

Through acetylation and conjugation.

21
Q

What happens to the acetylated metabolite of sulfonamides at neutral or acidic pH?

A

It precipitates, leading to crystalluria and potential kidney damage.

22
Q

How are unchanged sulfa drugs and their metabolites excreted from the body?

A

Via glomerular filtration and secretion.

23
Q

Can sulfonamides be eliminated in breast milk?

A

Yes, they may be eliminated in breast milk.

24
Q

What are the adverse side effects of sulfonamides?

A
  • Crystalluria.
  • Hypersensitivity.
  • Hematopoietic disturbances.
  • Kernicterus.
  • Drug potentiation.
25
Q

What is drug potentiation in the context of sulfonamides?

A

It refers to the increased effect of another drug when taken with sulfonamides.

26
Q

Who should not use sulfonamides?

A

Newborns, infants less than 2 months of age, pregnant women, and patients receiving methenamine.

27
Q

Why should patients receiving methenamine avoid sulfonamides?

A

Because they can crystallize in the presence of formaldehyde.

28
Q

What is the mechanism of action of Trimethoprim?

A

It is a potent inhibitor of bacterial dihydrofolate reductase, preventing the formation of the metabolically active form of folic acid (tetrahydrofolic acid) in bacterial cells.

29
Q

How does Trimethoprim exhibit selective toxicity?

A

It binds more readily to the bacterial enzyme than the human enzyme.

30
Q

What is the spectrum of activity of Trimethoprim?

A

Effective against both Gram-positive and Gram-negative bacteria.

31
Q

How much more potent is Trimethoprim compared to sulfonamides?

A

20-fold to 50-fold more potent.

32
Q

For which conditions can Trimethoprim be used alone?

A

Urinary tract infections (UTIs) and bacterial prostatitis.

33
Q

What are the resistance mechanisms to Trimethoprim?

A

Altered dihydrofolate reductase and decreased permeability.

34
Q

How is Trimethoprim absorbed?

A

Rapidly absorbed after oral administration.

35
Q

Where is Trimethoprim distributed in the body?

A

Widely distributed into body tissues and fluids, including CSF.

36
Q

What metabolic process does Trimethoprim undergo?

A

Undergoes some O-demethylation.

37
Q

What percentage of Trimethoprim is renally excreted?

A

60% to 80%.

38
Q

What electrolyte imbalance can Trimethoprim cause?

A

Hyperkalemia.

39
Q

What adverse effects are associated with Trimethoprim?

A

Effects of folic acid deficiency such as megaloblastic anemia, leukopenia, and granulocytopenia, especially in pregnant patients and those with nutrient-poor diets.

40
Q

How can the adverse effects of folic acid deficiency caused by Trimethoprim be reversed?

A

By using folinic acid (leucovorin).

41
Q

What is Cotrimoxazole a combination of?

A

Trimethoprim and sulfamethoxazole. It exhibits synergistic activity.

42
Q

How does the spectrum, resistance, PK, and adverse effects of Cotrimoxazole compare to its individual components?

A

They are similar to the individual drugs.

43
Q

What is Cotrimoxazole used to treat?

A
  • MRSA.
  • Respiratory infections – H. influenzae.
  • Septicemia and meningitis caused by Listeria monocytogenes.
  • Prostate infections and UTIs.
  • GIT infections (shigellosis and nontyphoid salmonella).
  • Toxoplasmosis gondii.
44
Q

What is the preferred treatment for Toxoplasmosis gondii?

A

Sulfadiazine and pyrimethamine.

Pharmacology (3) (15 decks)

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