Antiviral Drugs-Mechanism of Action,Selective & Resistance,Case studies & Group activity

1. ANTiviral drugs
CHEnnai
Dr Sumitha J

2. Antiviral agents
• Antiviral agents are medications used to treat viral infections
by inhibiting the replication of viruses or reducing their
ability to cause disease.

3. Types of Antiviral Agents
• Antiviral agents can be classified into several categories based on their mechanism of action:
• Entry Inhibitors: These drugs prevent the virus from entering host cells. Examples include fusion
inhibitors and attachment inhibitors.
• Nucleoside/Nucleotide Analogues: These drugs mimic the building blocks of DNA or RNA and
interfere with viral replication. Examples include acyclovir and tenofovir.
• Protease Inhibitors: These drugs target viral proteases required for viral replication. They are
commonly used in treating HIV and hepatitis C.
• Polymerase Inhibitors: These drugs inhibit viral enzymes (e.g., reverse transcriptase,
polymerase) involved in replicating the viral genome. Examples include zidovudine and
sofosbuvir.
• Neuraminidase Inhibitors: These drugs inhibit neuraminidase, an enzyme necessary for the
release of new virus particles. Oseltamivir is a well-known example.

4. Mechanism of Action
• antiviral agents interfere with specific stages of the viral life
cycle, including attachment, entry, replication, and release

5. Mechanism of Action
Attachment Inhibition: Viruses must first attach to specific receptors on
the surface of host cells to initiate infection. Antiviral agents can
interfere with this attachment process by:
• Competitive Binding: These agents mimic host cell receptors and compete with the virus for
binding sites. When the virus binds to the antiviral agent instead of the host cell receptor, it can't
initiate infection.
• Blocking Receptor Sites: Some drugs block or mask the viral binding sites on host cells, preventing
the virus from attaching.

6. Mechanism of Action
Entry Inhibition:After attachment, the virus needs to enter the host cell.
Antiviral agents can interfere with this step by:
• Fusion Inhibition: Fusion inhibitors, like enfuvirtide for HIV, block the fusion of viral and cellular
membranes, preventing the virus from entering the host cell.
• Endocytosis Inhibition: Some antiviral drugs can inhibit the endocytosis process that viruses use
to enter cells.

7. Mechanism of Action
Replication Inhibition: Once inside the host cell, viruses use the host's
machinery to replicate their genetic material and produce new viral
particles. Antiviral agents can disrupt this replication process by
targeting:
• Nucleoside/Nucleotide Analogues: These drugs resemble the building blocks of DNA or RNA and get
incorporated into the viral genome during replication, causing mutations and preventing further
replication. Examples include acyclovir and tenofovir.
• Protease Inhibitors: These drugs target viral proteases required for processing viral proteins,
preventing the formation of functional viral particles. They are commonly used in treating HIV and
hepatitis C.
• Polymerase Inhibitors: These drugs inhibit viral enzymes (e.g., reverse transcriptase, polymerase)
involved in replicating the viral genome.

8. Mechanism of Action
Release Inhibition:After replication, viruses must exit the host
cell to spread and infect other cells. Antiviral agents can
interfere with this release step by:
• Neuraminidase Inhibition: Neuraminidase is an enzyme required for the release of new
virus particles from host cells. Inhibiting this enzyme prevents the release of viruses.
Oseltamivir (Tamiflu) is an example used for influenza.

9. Selectivity and Resistance
• Selectivity of Antiviral Agents:
• Antiviral agents are designed to specifically target viral
processes, such as attachment, replication, or release, without
interfering with normal host cell functions. This selectivity is
essential for minimizing side effects and preserving the health of
the host.
• Selectivity is achieved by identifying unique viral targets or
processes that are distinct from those found in host cells. For
example, targeting viral enzymes or proteins that have no direct
equivalent in human cells.
• By specifically interfering with viral processes, antiviral agents
aim to disrupt the viral life cycle while leaving host cell functions

10. • Development of Drug Resistance:
• Viruses can develop resistance to antiviral agents over time due to
genetic mutations. This phenomenon is similar to the development of
antibiotic resistance in bacteria.
• When antiviral agents are used to treat viral infections, some viruses
may acquire mutations in their genetic material that confer resistance
to the drug. These mutations can occur naturally during viral
replication.
• Drug-resistant viral variants have changes in their viral targets (e.g.,
enzymes or proteins) that reduce the drug's ability to bind or inhibit
the viral process effectively. As a result, the drug becomes less
effective or completely ineffective against the resistant virus.
• The emergence of drug-resistant viruses is a significant concern in

11. Side effetcts
• Gastrointestinal Disturbances: Many antiviral drugs can cause
gastrointestinal side effects, including nausea, vomiting, diarrhea, or
abdominal discomfort. Patients should be advised to take these
medications with food or as directed to minimize these effects.
• Fatigue: Fatigue is a common side effect of antiviral therapy.
Patients may experience decreased energy levels and overall
tiredness.
• Headache: Headaches are often reported by individuals taking
antiviral drugs, particularly during the initial stages of treatment.
• Skin Reactions: Some antiviral drugs can lead to skin reactions,
such as rashes, itching, or hypersensitivity reactions. Patients

12. Side effetcts
• Liver and Kidney Function: Certain antiviral drugs can affect liver or
kidney function. Monitoring liver enzyme levels and kidney function
through blood tests is essential to detect any abnormalities early.
• Hematological Effects: Some antiviral drugs can cause
hematological side effects, including anemia, neutropenia (low white
blood cell count), or thrombocytopenia (low platelet count). Regular
blood tests are necessary to monitor these parameters.
• Psychiatric Symptoms: In some cases, antiviral therapy can lead to
mood changes or psychiatric symptoms. Patients and caregivers
should be educated about these potential side effects and
encouraged to seek help if necessary

14. Case Studies
• Case Study 1:Patient Scenario:
• A 28-year-old sexually active male presents with symptoms
of painful genital sores and flu-like symptoms. He has a
history of multiple sexual partners and has not been
consistently using protection. A clinical evaluation and
testing confirm a diagnosis of genital herpes (HSV-2
infection).

15. Group Activity
• Review the patient's medical history, symptoms, and
diagnostic results.
• Discuss the mechanisms of action of antiviral drugs used to
treat HSV infections.
• Recommend an appropriate antiviral treatment, including
the drug name, dosage, and duration of therapy.
• Consider the importance of patient education regarding
transmission prevention and managing recurrent outbreaks.

16. Case Studies
• Case Study 2:Patient Scenario:
• A 55-year-old patient with a history of intravenous drug use
presents with persistent fatigue, abdominal pain, and dark urine.
Laboratory tests show elevated liver enzymes, and further testing
confirms a chronic hepatitis C infection.

17. Group Activity
• Explore the mechanisms of action of antiviral drugs used to treat
chronic hepatitis C.
• Consider the patient's medical history, current symptoms, and
liver function tests.
• Recommend an appropriate antiviral treatment regimen,
including specific antiviral drugs, their doses, and duration.
• Discuss the potential side effects and drug interactions and how
to monitor and manage them.
• Highlight the importance of adherence and regular monitoring to
assess treatment response.

18. CASE STUDIES
• Case Study 3:Patient Scenario:
• A 45-year-old healthcare worker tests positive for COVID-19.
The patient is mildly symptomatic with fever, cough, and
fatigue. They have no known allergies or significant
comorbidities.

19. Group Activity
• Research and discuss the available antiviral treatments for
COVID-19.
• Consider the patient's mild symptoms, occupation, and
comorbidities.
• Recommend an appropriate antiviral treatment strategy,
including specific drugs (if applicable), dosages, and
duration.
• Discuss potential side effects and monitoring parameters for
COVID-19 treatment.
• Emphasize the importance of isolation, infection control