antiviral

Question 1

what are the common respiratory viral infections

Answer 1

• Influenza A and B
• Respiratory syncytial virus (RVS)
• Severe acute respiratory syndrome coronavirus 2(
SARS-CoV-2, COVID-19)
• Immunization is preferred for influenza and
COVID-19
• The antiviral agents are used when patients are
allergic to the vaccine ( influenza) or outbreaks
occur

Question 2

what is oseltamivir (Neuraminidase inhibitor)

Answer 2

Effective against both types of influenza
• Administered prior to exposure, prevent infection
• Administered within 24-48 hours after onset of symptoms, cause a
modest decrease in intensity and duration of symptoms

• MOA:
• Influenza viruses use a specific neuraminidase that is inserted in
the host cell membrane for releasing newly formed virions which is
essential for the virus life cycle
• Oseltamivir selectively inhibits this enzyme and prevents the
release of new virions and their spread from cell to cell

✓ Pharmacokinetics:
✓ An orally active prodrug , other members are given either by
inhalation or iv infusion
✓ Eliminated unchanged in urine
✓ Adverse effects:
✓ Most common are GIT

Question 3

what is remdesivir

Answer 3

✓ Prodrug of remdesivir triphosphate
✓ MOA:
✓ It is an adenosine analog , inhibits SARS-Cov-2 RNA-
dependant RNA polymerase
✓ This results in delayed chain termination and viral replication
✓ Therapeutic use:
✓ Treatment of hospitalized patients with COVID-19
✓ Route of administration: IV infusion
✓ Renal and hepatic function should be monitored before and
during therapy
✓ Adverse effects:
✓ Diarrhea , increased hepatic enzymes, anaemia,
hypersensitivity reactions

Question 4

what are herpes

Answer 4

• Herpes viruses are associated with a broad
spectrum of diseases:
• Cold sores, viral encephalitis, and genital
infections

Question 5

what is Acyclovir

Answer 5

✓ (acycloguanosine) is the prototypic antiherpetic
therapeutic agent.
✓ Herpes simplex virus (HSV) types 1 and 2, varicella-
zoster virus (VZV), and some Epstein-Barr virus–
mediated infections are sensitive to acyclovir.
✓ It is the treatment of choice in HSV encephalitis.
✓ The most common use of acyclovir is in therapy for
genital herpes infections.
✓ It is also given prophylactically to seropositive
patients before bone marrow transplant and post–
heart transplant to protect such individuals from
herpetic infections.

1. Mechanism of action:
   ✓ a guanosine analog, is monophosphorylated in the cell
   by the herpesvirus-encoded enzyme thymidine kinase

✓ Therefore, virus-infected cells are most susceptible.
✓ The monophosphate analog is converted to the di- and
triphosphate forms by the host cell kinases.
✓ Acyclovir triphosphate competes with deoxyguanosine
triphosphate as a substrate for viral DNA polymerase
and is itself incorporated into the viral DNA, causing
premature DNA chain termination.

2. Pharmacokinetics:
   ✓ Acyclovir is administered by IV, oral, or topical routes.
   [Note: The efficacy of topical applications is questionable.]
   ✓ The drug distributes well throughout the body, including
   CSF.
   ✓ Acyclovir is partially metabolized to an inactive product.
   Excretion into the urine occurs both by glomerular filtration
   and tubular secretion (Figure 34.9).
   ✓ Acyclovir accumulates in patients with renal failure.
   ✓ The valyl ester, valacyclovir, has greater oral bioavailability
   than acyclovir. This ester is rapidly hydrolyzed to acyclovir
   and achieves levels of the latter comparable to those of
   acyclovir following IV administration.
3. Adverse effects:
   ✓ Side effects of acyclovir treatment depend on the
   route of administration.
   ✓ For example, local irritation may occur from topical
   application;
   ✓ headache, diarrhea, nausea, and vomiting may
   result after oral administration.
   ✓ Transient renal dysfunction may occur at high
   doses or in a dehydrated patient receiving the drug
   IV.

Question 6

what is ganciclovir

Answer 6

✓ Ganciclovir is an analog of acyclovir that has greater activity against
CMV.
✓ It is used for the treatment of CMV retinitis in immunocompromised
patients and for CMV prophylaxis in transplant patients.
1. Mechanism of action:
✓ Like acyclovir, ganciclovir is activated through conversion to the
nucleoside triphosphate by viral and cellular enzymes. The nucleotide
inhibits viral DNA polymerase and can be incorporated into the DNA
resulting in chain termination.
2. Pharmacokinetics:
✓ Ganciclovir is administered IV and distributes throughout the body,
including the CSF.
✓ Excretion into the urine occurs through glomerular filtration and
tubular secretion (Figure 34.12). Like acyclovir, ganciclovir accumulates
in patients with renal failure

2. Pharmacokinetics:
   ✓ Valganciclovir, an oral drug, is the valyl ester of ganciclovir.
   ✓ Like valacyclovir, valganciclovir has high oral bioavailability, because
   rapid hydrolysis in the intestine and liver after oral administration leads
   to high levels of ganciclovir.
3. Adverse effects:
   ✓ Adverse effects include severe, dose-dependent neutropenia.
   Ganciclovir is carcinogenic as well as embryotoxic and teratogenic in
   experimental animals.

Question 7

what are the sites of antiviral drugs

Answer 7

viral absorption: blocked by enfuvirtide

viral uncoating blocked by amantadine

early protein synthesis blocked by fomicirsen

Nuclic acid synthesis blocked by purine analogs

late protein synthesis blocked by methisazone

packaging and assembly blocked by rifampin

viral release blocked by neuraminidase inhibitors