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Pharm Summer 2020 > Antibiotics that Inhibit DNA Replication and Folic Acid Synthesis > Flashcards

Antibiotics that Inhibit DNA Replication and Folic Acid Synthesis Flashcards

1
Q

How do fluoroquinolone inhibit DNA synthesis

A

Inhibit replication of DNA by interfering with DNA gyrase AND topoisomerase 4

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2
Q

Spectrum of fluoroquinolones

A

Relatively broad spectrum

Gram positive and negative

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3
Q

Precursor of fluoroquinolones

A

Naladixic Acid.

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4
Q

Is overuse of fluoroquinolones leading to resistance?

A

Yes.

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5
Q

How do fluoroquinolones enter bacteria

A

By passive diffusion. Inhibit replication of DNA by interfering with DNA gyrase AND topoisomerase 4

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6
Q

What do bacterial cells use DNA gyrase and topoisomerase 4 for?

A

Essential for maintaining DNA in a stable and biologically active form that can be replicated. Action of fluoroquinolones leaves DNA strand cleaved.

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7
Q

Are fluoroquinolones bacteriostatic or cidal?

A

Bactericidal activity. More pronounced as the concentration increases.

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8
Q

Ciprofloxacin.

  • not effective against
  • Most potent against
  • Drug of choice for
A
  • MRSA
  • Most potent against pseudomonas
  • Drug of choice for anthrax.
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9
Q

Levofloxacin

  • Isomer of
  • spectrum ?
A

Isomer of oflaxacin

Borad- Gram positive and negative

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10
Q

Moxifloxacin
Enhanced activity against gram __
Poor activity against __
Use for UTI?

A

Enhanced activity against gram positive
Poor activity against pseudomonas
Does not concentrate in urine, so is not good for UTIs. Rest of fluoroquinolones will work for UTIs.

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11
Q

Absorption of fluoroquinolones

A

Oral absorption is variable. Antacids, iron, zinc, and calcium can interfere.

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12
Q

Which fluoroquinolones have the longest half lives

A

Levofloxacin and moxifloaxacin. Allow once daily dosing.

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13
Q

Elimination of fluoroquinolones ?

Exception (moxifloxacin)

A

Mostly excreted really.

Moxifloxacin excreted by liver

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14
Q

Adverse reactions of fluoroquinolones

A
  • GI: nausea, vomiting, diarrhea
  • CNS toxicity: drugs bind to GABA receptors. Headaches, dizziness. New FDA warning that has serious mental health side effects.
  • Phototoxicity (Not as much as tetracyclines)
  • Connective tissue problems. Especially with cartilage.
  • FDA warning: Low blood sugar/hypoglycemia.
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15
Q

3 FDA warnings for fluoroquinolones

A
  1. Serious mental health side effects due to CNS toxicity.
  2. Low blood sugar/ hypoglycemia
  3. Now recommending avoiding the use of systemic fluoroquinolones when another alternative exists.
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16
Q

The FDA recommended avoiding using systemic fluoroquinolones. What does this mean for eye drops?

A

Pills- low on list of use.

Eye drops- totally fine. Topically formulations are fine for children even.

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17
Q

Avoid fluoroquinolones in who

A

SYSTEMIC fluoroquinolones. Pregnancy, nursing mothers, and children under 18 as it can cause cartilage erosion. Also avoid in patients with arrhythmia.

Except in cases of cystic fibrosis.

18
Q

fluoroquinolone drug interactions

A

Ciprofloxacin and ofloxacin increase theophylline levels. (bronchodilator) by interactions with P450.

All other fluoroquinolones raise levels of warfarin, caffeine, and cyclosporin.

19
Q

How do humans and bacteria get folate

A

Humans get folic acid from diet.

Many bacteria are impermeable to folic acid and make it on their own.

20
Q

Role of folate in cells

A

DNA and RNA synthesis depends on folate-derived cofactors. Cells cannot grow and divide without folate.

21
Q

Structure of sulfa drugs (Sulfonamides)

A

Structural analogues of PABA (intermediate in the synthesis of folate)

22
Q

Are sulfa drugs given alone

A

Rarely.

23
Q

How do sulfa drugs work?

A

Structural analogs of PABA. Compete with enzyme dihydroptoroate synthetase, an enzyme necessary for folate production and and inhibit it.

24
Q

Sulfa drugs

  • Spectrum
  • Not active against ___
  • _____ is resistant
A

Wide specturm
Not active against anaerobes
Pseudomonas is resistant
Any organism that can get folic acid from the environment would not be susceptible.

25
Q

Resistance to sulfa drugs

A

Organisms that can obtain folic acid from the environment are not sensitive.

Acquired resistance by altered enzyme, decreased cellular permeability so the drug can’t diffuse in, or enhanced production of PABA.

26
Q

Why do you not apply sulfa drugs topically?

A

Risk of sensitization/rash.

Sulfacetamide available in ocular formation. Similar to gentimyocin. Causes topical allergic rxn.

27
Q

Distribution of sulfa drugs

A

Bound to serum albumin
Penetrate well into CSF
Can pass placenta

28
Q

mEtabolism of sulfa drugs

A

Primarily in liver

Metabolites are without antimicrobial activity but can still be toxic.

29
Q

Excretion of sulfa drugs

A

Eliminated by kidney and breast milk

30
Q

Adverse effects of Sulfa drugs

A
  1. Crystalluria. Precipitate at neutral or acidic pH. Can cause nephrotoxicity.
  2. Hypersensitivities. Rashes, angio-edema, stevens johnson syndrome possible.
  3. Hemopoietic disturbances
  4. Kernicterus. Increased bilirubin in the CNS. Occurs in newborns.
  5. drug potentiation. Increases circulating warfarin levels.
31
Q

Trimethoprim MOA

A

Inhibits dihydrofolate reductase.
Prevents conversion of dihydrofolic acid to tetrahydrofolic acid.

Higher affinity for bacterial enzyme than mammalian.

32
Q

Trimethoprim spectrum

A

Similar to sulfa (broad spectrum gram positive and negative) but more potent. Therefore, can decrease dose.

33
Q

Resistance of trimethoprim

A

Develops in gram negative bacteria due to presence of altered enzyme.

34
Q

Trimethoprim. Drug is a weak ___. Accumulates in what kind of environments?

A

Weak base. Accumulates in acidic environments.

35
Q

Trimethoprim adverse effects

A

Folic acid deficiency. Especially in pregnant patients or those with poor diets (anemia, leukopenia, granulocytopenia)

Can co-administer with folinic acid

36
Q

Bactrim is a combo of

A

Trimethoprim and sulfamethoxazole

37
Q

Why is bactrim a combo of Trimethoprim and sulfamethoxazole

A

Has greater activity than either drug used alone
Similar half lives
Drugs work well together
Broader spectrum than sulfa drugs

38
Q

When is Bactrim effective

A
  • UTIs
  • Respiratory tract infections
  • Pneumocystis jiroveci. Causes pneumonia in immunocompromised patients.
  • Good against MRSA, especially skin and soft tissue infections.
39
Q

Resistance with Bactrim?

A

Less frequent. Requires simultaneous resistance to both drugs.

40
Q

Pharmacokinetics of Bactrim

A

Administered orally
Good volume of distribution
Excreted via kidney

41
Q

Adverse effects of Bactrim

A

Skin rash. Especially in elder.
Nausea, vomiting.
Anemias or thrombocytopenia
Caution in patients taking warfarin

Pharm Summer 2020 (18 decks)

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