PHA 520 - L2 Antivirals (Anti-infectives)

Why do antiviral drugs have the narrowest therapeutic index?

Viruses are obligate intracellular parasites that use the host cell's metabolic machinery to replicate, so antiviral drugs can also inhibit or damage host cell metabolism.

What is the key reason selective toxicity is difficult with antiviral drugs?

Viruses replicate inside host cells and depend heavily on host cell machinery, leaving fewer virus-specific targets that can be attacked without affecting the host.

What is selective toxicity?

The ability of a drug to kill or inhibit an invading organism without harming the cells of the host.

Why is selective toxicity easier with many antibacterial drugs than with antiviral drugs?

Bacteria have more biochemical and structural differences from animal cells, whereas viruses depend on the host cell's own metabolic machinery for replication.

What is a virus?

An obligate intracellular parasite that utilizes the host's metabolic machinery to replicate.

What does "obligate intracellular parasite" mean?

A virus must enter and use a living host cell in order to replicate.

What is the relationship between viral dependence on host cells and antiviral toxicity?

Because viruses use host cell processes for replication, interfering with viral replication can also interfere with normal host cell functions.

What does a narrow therapeutic index mean for antiviral drugs?

The difference between an effective antiviral dose and a dose that causes toxicity to the host is relatively small.

Are most antiviral drugs viruscidal or virustatic?

Virustatic; they inhibit viral replication rather than directly killing the virus.

What must a virustatic antiviral accomplish?

It must inhibit viral replication without destroying the host cell.

Why is early diagnosis of a viral infection important for antiviral therapy?

Most viral replication may have already occurred by the time clinical signs lead to diagnosis, making antiviral therapy less effective when started late.

Do antiviral drugs generally have broad or narrow spectra of activity?

Narrow spectra of activity.

What are the major therapeutic approaches of antiviral drugs?

Block viral attachment/fusion, block viral uncoating, inhibit viral DNA/RNA synthesis, inhibit specific viral enzymes, or stimulate the host immune system.

What do fusion inhibitors do?

Block viral attachment or fusion with host cells.

What do antimembrane drugs do?

Block uncoating of the virus.

How can antivirals interfere with viral genetic material?

They can inhibit viral DNA or RNA synthesis.

What viral enzymes can be targeted by antiviral drugs?

Proteases, integrases, and neuraminidases.

Why are antivirals used relatively infrequently in veterinary medicine?

Their use is limited partly because of significant expense.

What is the major antiviral "take-home" concept from this lecture?

Antivirals have the narrowest therapeutic index because viruses replicate using host cell machinery, making it difficult to inhibit the virus without also affecting the host cell.