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Antiviral drugs (antivirals) are medicines that are used to treat or prevent the infections caused by virus. Antivirals act specifically against particular groups of viruses and its actions are limited to these groups alone. A virus has no cell membrane and can multiply when it infects a cell’s nucleus in the human (host) body. The virus invades the host cells and multiplies rapidly thereby resulting in the particular infection.
Common viral infections in humans includes the herpes virus (shingles, chickenpox and oro-genital herpes), cytomegalo virus (CMV) retinitis, hepatitis (A, B, C), papilloma virus (warts), rubella, rabies, polio, influenza, measles, mumps, HIV and SARS. Some infections are mild like the and the body immunity can contain the infection without any antiviral medications in healthy individuals. However other infections can cause long term complications or even result in death and needs to be treated as soon as possible.
Antivirals are useful against diseases like herpes infections, hepatitis B and C infections, influenza, HIV, viral warts, respiratory syncytial virus (RSV) infection, CMV infection.
Acyclovir and valacyclovir are used for herpes infections. High dose acyclovir can be used to prevent CMV infections in AIDS patients (immunocompromised). Acyclovir is given orally, intravenously and topically as eye (not available in the US) and skin ointments. Valacyclovir is available for oral use. Peniciclovir and famiciclovir are drugs with similar profile available outside the US. Docosanol cream is available for herpes treatment as over-the-counter medicine. Idoxuridine and trifluridine are applied topically for herpes keratitis (corneal infection).
Ganciclovir and valganciclovir are available for treating CMV infection (retinitis) and prevention of CMV infection in AIDS and transplant patients. Ganciclovir is available for oral use, intravenous and intraocular injections, ocular implant and ophthalmic gel. Valganciclovir is only available orally. Other drugs available for resistant CMV infections are foscarnet (intravenous), fomivirsen (intraocular) and cidofovir (intravenous). Cidofovir and foscarnet are also useful in resistant herpes infections.
Drugs like zidovudine, stavudine, didanosine, zalcitabine, lamivudine, tenfovir, lopinavir, nevirapine, efavirenz, indinavir and so on are some of the drugs that are used to treat HIV infection (antiretrovirals).
Oseltamivir (oral) and zanamivir (oral inhalational) are used for the prevention and treatment of influenza infections. Amantadine and rimantadine are used orally for prevention and treatment of influenza A virus, but less effective than former ones.
Oral ribavirin is used against hepatitis C infection while aerosol ribavirin is approved for RSV infections.
Adefovir is used orally for treatment of chronic hepatitis B infection. Intramuscular or subcutaneous interferons are used in chronic hepatitis B and C infections, papilloma virus infection (condylomata acunimatum) and Kaposi’s sarcoma of HIV.
Antiviral drugs mainly inhibit the replication of the virus in the host cell by inhibiting DNA, RNA or protein synthesis by the virus. Some antiviral drugs may also help in stimulating the immune system of the body so that the body itself combats the disease.
Nausea or vomiting, diarrhea, fever, dizziness, rash, lightheadedness, headache, sleep problems, concentration problems, and irritability or nervousness are the adverse effects generally seen with the antiviral drugs. Other unique side effects for individual drugs (if any) are discussed below.
Acyclovir and valacyclovir can rarely cause renal toxicity or neurotoxicity and high doses can cause abnormal blood counts.
Ganciclovir and valganciclovir can cause bone marrow suppression and abnormal blood counts. They can also cause behavioral side effects. Foscarnet and cidofovir are toxic to kidney and fomivirsen can cause iritis.
Antiretroviral drugs can cause fatal allergic reactions, bone marrow suppression, pancreatitis, neuropathy, muscle pain and liver toxicity.
Zanamivir can cause wheezing and bronchospasm and hence is ideally avoided in asthma and bronchitis patients. Aerosol ribavirin can cause wheezing while oral ribavirin can cause bone marrow suppression.
Adevofir is toxic to kidney. Interferons can cause bone marrow suppression, neurotoxicity, fall in blood pressure and increased heart rate.
Pregnant and lactating women should take antiviral medication only under the treating doctor’s advice.
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