antiviral

Antiviral Drugs

Classification of viral infections
Herpes simplex and varicella-zoster
Human immunodeficiency
Influenza A
Cytomegalovirus
Respiratory Syncytial virus (RSV)
Drugs that modulate the host immune system

Herpes simplex and varicella-zoster

Aciclovir
Valaciclovir
famciclovir

Aciclovir

Mechanism of action
Inhibits viral DNA synthesis only after phosphorylation by virus-specific thymidine kinase.
The phosphorylated aciclovir inhibits DNA polymerase in the virus and so prevents virus DNA formation


Aciclovir
It is effective against susceptible Herpes viruses if started early in the course of infection, but it does not eradicate persistent infection because viral DNA is integrated in the host genome.

Aciclovir

Clinical uses
Herpes simplex virus
Skin infections, including initial and recurrent labial and genital herpes
Ocular keratitis
Encephalitis, disseminated disease (IV)

Aciclovir (clinical uses)

Varicella-zoster virus
Chickenpox, particularly in the immunocompromised (IV) or in the immunocompetent with pneumonitis or hepatitis (IV)
Shingles in immunocompetent persons

Aciclovir

Adverse effects
Ophthalmic ointment causes a mild transient stinging sensation
gastrointestinal symptoms, headache, and neuropsychiatric reactions.

Human immunodeficiency

Nucleoside reverse transcriptase inhibitors
Protease inhibitors
Non- nucleoside reverse transcriptase inhibitors
Entry inhibitor


Nucleoside reverse transcriptase inhibitors
Zidovudine (Retrovir)
Didanosine
Lamivudine

Zidovudine (Retrovir)

Mechanism of action
Has a high affinity for HIV’s reverse transcriptase and is integrated by it into the viral DNA chain causing premature chain termination. The drug must be present continuously.

Zidovudine (Retrovir)

Clinical uses
Serious manifestations of HIV infection in patients with acquired immunodeficiency syndrome or AIDs related complex

Zidovudine (Retrovir)

Adverse effects
Anorexia, nausea, vomiting, Headache, dizziness, Malaise and myalgia
Anemia and neutropenia
Hepatic necrosis

Protease inhibitors (amprenavir)

Mechanism of action
In its process of replication, HIV produces protein and also a protease, which cleaves the protein into component parts that are subsequently reassembled into virus particles; protease inhibitors disrupt this essential process


Protease inhibitors
Adverse effects
GIT disturbance, headache, dizziness, sleep disturbance, pancreatitis, neutropenia, and rashes.

Non-nucleoside reverse transcriptase

Used in africa HIV1
Efavirenz

Entry inhibitor

Enfuvirtide
is the first antiretroviral agent to target the host cell attachment/entry stage in the HIV replicaton cycle.

Influenza A

Amantadine
Zanamivir
Oseltamivir (Tamiflu)

Amantadine

Is only effective only against influenza A; it acts by interfering with the uncoating and release of viral genome into the host cell.

Amantadine

Clinical Uses
Used orally for the prevention and treatment of infection with influenza A virus


Adverse effects
Dizziness, nervousness, and insomnia

Zanamivir

Is a viral neuraminidase inhibitor that blocks both entry of influenza A and B viruses to target cells.

Oseltamivir (Tamiflu)

Is an oral pro-drug of a viral neuraminidase inhibitor. it reduces the severity and duration of symptoms caused by influenza A or B
Is one option for treatment and prophylaxis of avian H5N1 influenza

Cytomegalovirus

Ganciclovir
Resembles aciclovir in its mode of action, but is much more toxic

Respiratory syncytial virus (RSV)

Ribavirin is a synthetic nucleoside used for RSV bronchiolitis in infants and children, inhaled by a special ventilator.

Drugs that modulate the host immune system

Interferons
Directly on uninfected cells to induce enzymes that degrade viral RNA
Indirectly by stimulating the immune system
To modify cell regulator mechanisms and inhibit neoplastic growth


Drugs that modulate the host immune system
Interferons
Interferons are cassified as alfa, beta, gamma according to their antigenic and physical properties.
Interferon alfa 2 a and 2b also improve the manifestations of viral hepatitis.
Adverse effects
Are common and include an influenza-like syndrome

Drugs that modulate the host immune system

Imiquimod
is used topically for genital warts (caused by papillomaviruses). Treatment for 2-3 months results in gradual clearance of warts in about 50% patients.