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Principles of Therapy Core Drugs > Nucleic Acid Synthesis Inhibitors > Flashcards

Nucleic Acid Synthesis Inhibitors Flashcards

1
Q

What is another name for sulphonamides?

A

antimetabolites

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2
Q

What is the mechanism of action of sulphonamides?

A

Compete with p-aminobenzoic acid (PABA), as a false substrate for the enzyme dihydropteroate synthetase, in the synthesis of folic acid.

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3
Q

What are Sulphonamides structural analogues of?

A

p-aminobenzoic acid (PABA)

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4
Q

What is p-aminobenzoic acid (PABA) essential for in bacteria?

A

synthesis of folic acid

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5
Q

What is the spectrum of activity of sulphonamides?

A

Wide, Gram + and - bacteria

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6
Q

Where are most sulphonamides absorbed?

A

GIT

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7
Q

After how long do sulphonamides reach maximum plasma concentrations?

A

4-6 hours

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8
Q

Which sulphonamide is applied topically? (exception)

A

silver sulfadiazine

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9
Q

What form of administration is not used with most sulphonamides?

A

topical

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10
Q

Which organ metabolises sulphonamides?

A

liver

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11
Q

How are sulphonamides excreted?

A

acetylated derivative is excreted in the urine

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12
Q

What are the adverse effects of sulphonamides? (3)

A
  • common: nausea, vomiting, headache
  • crystaluria
  • pregnancy: kernicterus in newborns
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13
Q

What are the contraindications of sulphonamides?

A

Patients with porphyria

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14
Q

What is the classification of trimethoprim?

A

diaminopyrimidine derivative

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15
Q

What is the mechanism of action of trimethoprim?

A

Inhibits bacterial dihydrofolate reductase enzyme

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16
Q

What does the enzyme dihydrofolate reductase do? (and what happens after this?)

A

converts dihydrofolic acid to tetrahydrofolic acid (active), a stage leading to the synthesis of purines and ultimately to DNA

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17
Q

What is co-trimoxazole?

A

A combination of trimethoprim and sulfamethoxazole (sulphonamide)

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18
Q

What are the therapeutic indications of co-trimoxazole? (5)

A
  • Urinary tract, respiratory tract and prostatic infections
  • prophylaxis
  • Pneumocystis jirovecii (causes pneumonia in patients with AIDS)
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19
Q

When is co-trimoxazole well absorbed?

A

After oral administration

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20
Q

Describe the distribution of co-trimoxazole in body tissues and fluids

A

widely distributed

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21
Q

What is the volume of distribution of trimethoprim and sulfamethoxazole?

A

100L

22
Q

What is the % of sulfamethoxazole bound to plasma proteins?

A

70%

23
Q

What is the % of trimethoprim bound to plasma proteins?

A

44%

24
Q

How is trimethoprim excreted and where?

A

unchanged in the urine

25
Q

Where is sulfamethoxazole metabolised?

A

liver

26
Q

What are the adverse effects of co-trimoxazole? (6)

A
  • nausea, vomiting, blood disorders and skin rashes

- folate deficiency, with resultant megaloblastic anaemia

27
Q

What is the classification of ciprofloxacin?

A

Fluoroquinolone

28
Q

What is the mechanism of action of Fluoroquinolones?

A

Inhibits the function of topoisomerases, bactericidal

29
Q

What is the spectrum of action of Flouroquinolines?

A

Similar to aminoglycosides

30
Q

How are Flouroquinolines administered?

A

orally

31
Q

How is ciproflaxin administered?

A

IV, rapidly and well-absorbed orally

32
Q

Describe the distribution of ciproflaxin in body tissues and fluids

A

widely distributed

33
Q

Which parts of the body are penetrated by ciproflaxin?

A

tissues, bone, kidney, prostate, lung

34
Q

What is the half-life of ciproflaxin?

A

4-5 hours

35
Q

How is ciproflaxin metabolised?

A

In the liver by the cytochrome P450 enzyme system

36
Q

How is ciproflaxin excreted?

A

oral dose is excreted unchanged in the urine.

37
Q

What are the therapeutic indications of flouroquinolines? (4)

A
  • Gram negative bacteria
  • Gram positive bacteria
  • Moxifloxacin more active against G+ and S. pneuomoniae
  • Useful in respiratory tract infections in patients with beta-lactam allergy
38
Q

What are the adverse effects of Flouroquinolines? (6)

A
  • well-tolerated: GIT/skin rashes
  • theophylline toxicity in asthmatics
  • hepatotoxicity, prolonged QT interval, GIT disturbances, hypersensitivity reactions
39
Q

What are contraindications of flouroquinolines?

A

pregnancy and children under 18

40
Q

What is the classification of Metronidazole?

A

Nitroimidazole

41
Q

What is the mechanism of action of Metronidazole?

A

Selective toxicity against anaerobes

42
Q

What are the therapeutic indications of Metronidazole? (3)

A
  • Antiprotozoal against trophozoites of Entermoeba histolytica and Trichomonas vaginalis
  • Eradicate H. pylori (peptic ulcer tx)
  • Potent antibacterial activity against anaerobes
43
Q

How is Metronidazole administered?

A

orally (rapidly and completely absorbed), rectal and IV

44
Q

When is a peak plasma concentration reached with Metronidazole?

A

1-3 hours

45
Q

What is the half-life of Metronidazole?

A

7 hours

46
Q

Describe the distribution of Metronidazole

A

distributed rapidly throughout the tissues including the cerebrospinal fluid

47
Q

In which organ is Metronidazole metabolised?

A

liver

48
Q

How is Metronidazole excreted?

A

unchanged in the urine

49
Q

What are the adverse effects of Metronidazole? (4)

A
  • metallic, bitter taste in the mouth
  • GIT disturbances
  • When combined with alcohol: disulfiram-like reaction
  • Mutagenic, carcinogenic and teratogenic
50
Q

What are contraindication of Metronidazole?(3)

A
  • cannot be used for more than 10 days
  • pregnancy/breastfeeding
  • alcohol consumption

Principles of Therapy Core Drugs (8 decks)

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