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Antiviral Chemo Flashcards

1
Q

Zanamivir; Oseltamivir

A

Influenza drugs

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2
Q

Ribavirin

A

RSV; Hep C

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3
Q

Acyclovir

A

Herpes Viruses

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4
Q

Ganciclovir; Foscarnet; Cidofovir

A

CMV Drugs

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5
Q

Tami-Flu =

A

Oseltamivir

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6
Q

Neuraminidase is unique to

A

Influenza viruses

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7
Q

Neuraminidase function

A

Helps virus leave infected cells by cleaving sialic acid from glycoproteins on infected cells.

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8
Q

Zanamivir/Oseltamivir MOA

A

Neuraminidase inhibitors. Must be administered within 48 hours of onset. No significant side effects.

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9
Q

Administration of Zanamivir vs Oseltamivir

A

Zanamivir: Inhalation
Oseltamivir: Oral

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10
Q

First step of viral pharmacokinetics

A

Get into IC fluid

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11
Q

Viral life cycle

A

Early Proteins: Polymerases that transcribe and translate viral proteins.
Synthesis of Nucleic Acids: Replicate viral genome. Additional copies required for proliferation.
Late Proteins: Structural; Make viral capsule

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12
Q

What part of the viral life cycle do most antivirals target?

A

Nucleic Acid Synthesis (block polymerases/replication of viral genome).

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13
Q

Adverse effects of Ribavirin

A

Dose-dependent anemia (10-20%); fatigue, rash, pruritis. Known teratogen and embryotoxin.

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14
Q

Protein synthesis is not a target of antivirals because

A

Viruses use host machinery to make proteins

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15
Q

Describe the two stages of selective toxicity.

A
  1. Kinases needed on nucleoside analogs to place phosphate groups on. This generates nucleotide triphosphate.
  2. Selectivity of viral polymerase to nucleotide triphosphate analog
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16
Q

Adverse effects of Acyclovir

A

Minimal: Nausea, headache

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17
Q

Major mechanism of resistance for Acyclovir

A

Thymidine Kinase Negative Viruses result in inability to place phosphate groups and generate nucleotide triphosphate analogs.

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18
Q

Telaprevir Side Effects

A

Rash/pruritis (30-55%), fatigue, GI, anemia

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19
Q

Simeprevir Side Effects

A

Photosensitivity, Rash

Contains Sulfa moiety so Hypersensitivity, Stevens-Johnson

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20
Q

Nucleotides used to transcribe DNA and RNA

A 
Triphosphate Form
Each nucleotide has
-Ribose sugar
-Attached base
-3 phosphate groups
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21
Q

How do DNA/RNA Polymerase work?

A

DNA/RNA Polymerase pick up nucleotide building blocks in the triphosphate form.
Enzyme cleaves off two phosphate groups and leaves one phosphate group attached.
Phosphate group attached is used to form backbone.

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22
Q

How do antiviral drugs work?

A

Antiviral drugs mimic structure of one of the nucleotides
Virus picks up the drug, thinking that it is the nucleotide
Virus incorporates the drug/analog into its strand of DNA or RNA
Once drug is incorporated, chain can no longer grow (termination)
“Inhibitors” of RNA/DNA polymerase

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23
Q

Many antiviral drugs mimic what?

A

Nucleotides (they are nucleotide analogs)

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24
Q

Antiviral drugs need to become what in order to work?

A

Tri-phosphorylated (like nucleotides)

Necessary to be incorporated into growing DNA/RNA chain

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25
What type of enzyme phosphorylates nucleosides to become nucleotides?
Viral kinase and/or cellular kinases of infected cell
26
What is a common mechanism of resistance to antiviral drugs?
Mutation of viral kinases | Drug is no longer effective b/c it can no longer recognize virus
27
Ribavirin is an analog of what nucleotide?
Guanosine
28
How is Ribavirin different from Guanosine?
Base attached to ribose molecule is altered structure | When RNA Polymerase binds Ribavirin, it is inhibited because correct nucleotide binding is prevented (termination)
29
What enzymes are used to triphosphorylate Ribavirin?
Kinase enzymes in infected cell
30
What is overall result of Ribavirin?
Decrease in viral replication | Production of defective virions
31
In addition to RNA Polymerase, what other enzyme does Ribavirin inhibit?
``` IMP Dehydrogenase (Inosine monophosphate dehydrogenase) Biochemical intermediate that gets converted by cells into guanosine nucleotides ```
32
Describe the MOA of IMP dehydrogenase
Binds Ribavirin b/c it thinks it is an IMP molecule IMP is inhibited by Ribavirin Pool of available guanine nucleotides is decreased (viruses cannot build as many copies of their genomes)
33
Describe uses of Ribavirin.
1. RSV in children - Clinical trials show no benefit. Last resort or immunocompromised 2. Ribavirin can be added to interferon for Hep C treatment
34
What is a key side effect of Ribavirin?
Hemolytic anemiam (10% pts) - Drug accumulates inside RBCs - Depletes phosphate pool in RBCs leading to ATP deficiency - Can be very severe
35
Is Ribavirin a teratogen?
Yes
36
Describe MOA of Acyclovir.
Inhibitor of herpes virus DNA polymerase - Herpes virus can synthesize its own DNA polymerase - Acyclovir inhibits this polymerase b/c it is a guanosine analog - Termination of chain growh
37
How are Guanosine and Acyclovir different?
Acyclovir is missing a ribose sugar.
38
Describe phosphorylation of Acyclovir which allows it to be taken up by DNA polymerase?
First phosphate group added by herpes virus thymidine kinase. - This creates a targeted effect b/c it only occurs in infected cells - Infected cell becomes acyclovir monophosphate - Monophosphate is triphosphorylated by cellular enzymes
39
What is Acyclovir an analog of?
``` deoxyguanosine triphosphate (dGTP) -Mistakenly taken up by viral DNA polymerase, terminating chain growth ```
40
How do viruses develop resistance to Acyclovir?
Decrease amount of viral thymidine kinase produced Alter viral thymidine kinase structure Alter viral DNA polymerase structure to decrease binding to acyclovir triphosphate
41
Valacyclovir
Pro-drug, converted to acyclovir. | Has greater bioavailability than acyclovir so lower dose can be used
42
Side Effect of Acyclovir
Generally well tolerated. However, IV administration of acyclovir can cause nephrotoxicity b/c it crystalizes in urine. Given with IV fluids to reduce risk of complication.
43
Acyclovir is effective for what infections?
``` HSV-1 HSV-2 VZV (eg. Shingles) Genital Herpes Herpes Labials Herpes Encephalitis Herpes Zoster ```
44
Why isn't acyclovir effective for EBV and CMV?
They have a different viral kinase so cannot phosphorylate acyclovir
45
Describe "suppressive" therapy of acyclovir.
HSV-1, HSV-2 and VZV can lie dormant in nerves and reactivate. Pts with frequent reinfections with genital or oral herpes will take acyclovir to prevent flare ups
46
CMV infections are associated with what?
``` HIV/Aids Transplant patients (chronic immunosuppressive drugs) ```
47
What are the key drugs to treat CMV infection? How do they work?
Ganciclovir Foscarnet Cidofovir All interfere with CMV DNA polymerase
48
Ganciclovir
Ganciclovir has similar MOA to Acyclovir because it is a Guanosine Analog - Ganciclovir gets IC converted by CMV viral kinase to become Ganciclovir 5'-Monophosphate - Triphosphorylation by cellular enzymes so it can mimic deoxyguanosine triphosphate (dGTP) - Subsequent incorporation terminates chain growth
49
What is the major toxicity of Ganciclovir?
Bone marrow suppression - Leukopenia (low WBC) - Occurs because Ganciclovir also inhibits bone marrow DNA polymerase (in addition to viral DNA polymerase)
50
Valganciclovir
Pro-drug that is converted to Ganciclovir | Has better bioavailability
51
Why is Ganciclovir primarily administered by IV?
``` Poor Bioavailability Oral valganciclovir (better bioavailability) often preferred. Can be orally administered. ```
52
Foscarnet is an analog of what?
Pyrophosphate | -Mimics structure of phosphate group
53
Describe MOA of Foscarnet
DNA polymerase thinks it is a normal phosphate group on a triphosphonucleotide - DNA phosphorylase binds to Foscarnet and is inhibited (cannot cleave phosphate groups off triphosphonucleotide) - DNA chain can no longer elongate
54
When is Foscarnet used?
CMV infection when Ganciclovir fails | Acyclovir-resistant HSV and VZV infections
55
What are the side effects of Foscarnet?
Nephrotoxicity (limiting side effect; kidney failure) Hypocalcemia due to calcium chelation Induces renal wasting of magnesium (hypomagnesaemia) Seizures MUST MONITOR ELECTROLYTES
56
Cidofovir is a nucleotide analog of what?
Cytidine
57
Is viral kinase required for Cidofovir to inhibit DNA polymerase?
No. Cidofovir phosphorylation occurs via cellular kinases
58
How is Cidofovir different from Cytidine?
Cidofovir is missing ribose sugar. Once it is contributed to DNA chain termination occurs.
59
What is the main use of Cidofovir?
CMV retinitis
60
What is the main toxicity of Cidofovir?
Renal failure Anion transporter in proximal tubule that binds Cidofovir This results in high concentrations of Cidofovir in the renal cortex Reduce complication by co-administering with saline to flush kidneys Can also reduce complication by using Probenecid (gout drug) which blocks renal tubular secretion of Cidofovir into urine. Accumulation of Cidofovir in tubular cells is reduced.
61
What are interferons?
Cytokines Glycoproteins that are synthesized by infected cells and lymphocytes Numerous immunomodulatory effects
62
What does Interferon alpha do?
Primes cells to fight against viruses
63
What is Interferon alpha administered for?
``` Hep B & C (decreases viral replication) Kaposi Sarcoma (skin lesion in HIV/AIDs pts; caused by HHV-8) ```

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