Viruses are parasites that cannot reproduce on their own. They recognize specific molecules on the surface of target cells and bind to them. After entering the cells, viruses take off their protein coat'a process called un-coating'to release the genome (DNA or RNA). They use the host cell's tools to reproduce themselves. Released viruses find new host cells to infect. Antiviral medications prevent viral entry, un-coating, replication of viral genome (DNA or RNA), re-coating and spread of viruses to new host cells.
Anti-influenza
Amantadine (trade name Symmetrel®) and Rimantadine (Flumadine®) prevent viruses from un-coating, so that they cannot release their genome into the host cells and infect them. Zanamivir (Relenza®) and Oseltamivir (Tamiflu®) inhibit the release of newly formed viruses from the host cell, and thus prevent the spread of infection.
Anti-herpes Virus
Oral herpes simplex virus (HSV) causes cold sores around lips, and genital HSV causes genital herpes. Medications for their treatment can also be used against another herpes virus, Varicella zoster virus (VZV) that causes chicken-pox in children and shingles in adults. Acyclovir (Zovirax®) and Valaciclovir (Valtrex®) inhibit viral DNA synthesis. Idoxuridine and Brivudin (Zostex®) can be incorporated into the viral DNA leading to reduced functioning of the DNA.
A third type of herpes viruses with established treatment is cytomegalovirus (CMV), particularly dangerous for unborn children, infants and immune-compromised patients. Medications used to treat CMV are Ganciclovir and Foscarnet, also indicated in some HSV infections. They act to inhibit viral DNA synthesis.
Anti-HIV
Antiviral medications used to control, but unfortunately not cure HIV infections comprise a large and diverse group of drugs.
Viral entry inhibitors'such as Enfuvirtide'prevent newly formed viruses to enter uninfected host cells by preventing virus-cell fusion.
Reverse transcriptase is an enzyme that HIV needs to form DNA from its RNA in order to duplicate it. Reverse transcriptase inhibitors include many drugs'such as Abacavir, Lamivudine, Zidovudine, Tenofovir, Efavirenz and Nevirapine.
Another approach is to inhibit assembly of new viruses, when host cell enzymes'proteases'cut large proteins into smaller building blocks of new viral coats. Atazanavir, Indinavirn and Ritonavir are such protease inhibitors.
Combination therapies (triple drug cocktails) are very effective and can reduce viral load in the patient below detectable levels.
Anti-hepatitis
One of the few anti-HBV medications is Lamivudine'a reverse transcriptase inhibitor. Adefovir dipivoxil, used against HIV too, also inhibits transcription of viral RNA into DNA.
Infected cells produce their own antiviral molecules---interferons. They detect the virus, bind to host cells and help the immune system fight the infection. There are drugs'such as Imiquimod 'that can push the body to produce its own interferons. Synthetically produced Alpha-interferon is effective in treatment of HBV and HCV, especially in combination with other drugs.
Broad-spectrum Antiviral Medications
Ribavirin (Virazole®) is effective in the treatment of HCV and paramyxoviruses (measles and respiratory syncytial virus). It inhibits an enzyme that synthesizes one of the necessary building blocks of viral genome. As an anti-influenza medication, Ribavirin blocks synthesis of viral RNA. A combination of Ribavirin and Alfa-interferon is proven to be effective in treatment of chronic hepatitis C infections.
References
- "Microbiology: An Introduction"; Gerarad J. Tortora, Berdell R. Funke Ph.D. and Christine L. Case; 2007
- "Medical Microbiology": "Chemotherapy of viral infections"; Erik De Clercq, M.D. Ph.D.; 1996
- "Journal of Clinical Virology"; Antiviral drugs in current clinical use; Erik De Clercq, M.D. Ph.D.; June 2004
