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List of eight important antiviral drugs:- 1. Aciclovir 2. Famciclovir and Valaciclovir 3. Ganciclovir 4. Foscarnet 5. Cidofovir 6. Tribavirin 7. Amantadine 8. Zanamivir.
Aciclovir is active against herpes viruses, but does not eradicate them. It is effective only if started at the onset of infection. Orally, aciclovir is about 20% absorbed and is widely distributed including the CSF. Aciclovir, by intravenous infusion is the drug of choice for treatment of herpes simplex in the immunosuppressed patients, severe initial genital herpes, varicella zoster (chicken pox) and herpes meningoencephalitis.
Oral aciclovir is effective in accelerating the healing of genital herpes, in preventing damage to the eye on involvement of ophthalmic branch of the trigeminal nerve by herpes zoster (shingles) and chickenpox in immunocompetent adults. Topical aciclovir is used to treat ulceration of the cornea due to herpes simplex virus and labial herpes.
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Aciclovir, intravenously, can cause severe local inflammation, hallucinations, tremors, psychosis, convulsions and coma. Orally, aciclovir is well tolerated, however, GIT disturbances, rashes, neurological reaction including dizziness and headache can occur. Topical applications can cause local discomfort and pruritis. It is contraindicated in pregnancy.
These are pharmacologically similar and are given orally to treat herpes simplex, herpes zoster and suppression of initial and recurrent genital herpes. They have the advantage of less frequent oral administration.
Ganciclovir is related to aciclovir, but is more active against cytomegalovirus (CMV). It is used in life threatening or CMV retinitis in immunosuppressed patients, e.g. those with AIDS. It is available for intravenous infusion. It can be inserted surgically into the eye as slow release ocular implants. Orally, it is used for maintenance treatment of CMV retinitis, following intravenous therapy. The most serious side effect is suppression of white cell count and of the platelets. It is contraindicated during pregnancy.
Foscarnet is reserved for CMV retinitis in AIDS patients and mucocutaneous herpes simplex virus infections, non-responsive to aciclovir in immunosuppressed patients. It is given by intravenous infusion and is highly nephrotoxic.
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Cidofovir is used in the treatment of CMV retinitis in AIDS patients, when ganciclovir and foscarnet are contraindicated. It is given in combination with probenecid. It is nephrotoxic.
Tribavirin is used in the treatment of severe respiratory syncytial virus (RSV) bronchiolitis in infants and children. It is given by nebulizer or aerosol inhalation. Side effects include worsening of respiration, bacterial pneumonia and rarely anemia and hemolysis.
Amantadine has some action against the influenza virus and can be used for prophylaxis during an outbreak of influenza A only. It can be used in Parkinson’s disease when levodopa is contraindicated, as it increases the concentration of dopamine in basal ganglia. Side effects include nausea, central effects and swelling of the ankles.
Zanamivir is used in the treatment of influenza A or B within 48 hours after onset of symptoms, when influenza is epidemic in the community. It is given by nebulizer or aerosol inhalation. It is doubtful, if it prevents complications in high-risk patients, who are better immunized. Side effects include GIT disturbances, bronchospasm and rashes.
