Antiviral drugs

Antiviral drugs act by inhibiting the duplication and further development of viruses that have infected cells of the body. However, unlike with antibiotics, the offending organism is not killed but only stopped. All antivirals work by stopping duplication of genetic material, DNA or RNA, present in the virus and thereby preventing its proliferation and continued infection. As viruses invade and rely on human cells for their survival, it is especially tricky to create medicines that target only the virus and don’t harm the host body. Most antivirals are virus-specific and act primarily on a particular kind of virus. However, as all of these drugs work on the same principle of action, sometimes a drug may prove effective against microorganisms other than the one it is intended for. Following are some of the types of antiviral drugs:

• Anti-herpes virus: These drugs work on viruses from the herpes group, including herpes simplex virus 1 (HSV-1), which causes cold sores around the mouth, herpes simplex virus 2 (HSV – 2 ), which causes genital herpes, and Varicella zoster virus (VZV), which causes chickenpox and shingles. The most commonly used anti-herpes drug is acyclovir. Acyclovir works by combining with an enzyme the virus produces to form a substance that prevents further DNA synthesis, effectively ending the viral infection. Acyclovir is administered in many forms depending on the site of infection. It can be used as oral tablets, eye drops and skin ointments as well. Side effects can include a burning sensation on the site of application, headache, nausea, fall in blood pressure and reduction in urine output (at high doses). Reversible manifestations like tremors, hallucinations and disorientation can occur rarely.
• Anti-influenza virus: These are specifically designed to work on flu-causing (influenza) viruses. They are effective against various strains of the influenza virus. While most viral flu infections are self-limiting (they resolve on their own), in some cases, like H1N1 (swine flu) and H5N1 (bird flu), medicines like oseltamivir (Tamiflu) are required. Oseltamivir works by inhibiting a viral enzyme that is the key component responsible for virus regeneration. However, each year this enzyme component of the virus undergoes mutation (changes occur in its genetic material) and the virus becomes resistant to the drug. In such cases, other medicines like zanamivir, which come in a powder form intended for inhalation, are considered. Oseltamivir is the most effective drug against the flu and is taken orally in tablet form. It both prevents and fights infection if taken in time. Side effects can include stomach ache, nausea, diarrhea, sleepiness and altered taste sensation.
• Anti-hepatitis drugs: These were created to combat hepatitis or liver infections, caused by hepatitis causing viruses. Hepatitis can occur due to various reasons including viruses. Viral hepatitis is commonly caused by Hepatitis A Virus (HAV), Hepatitis B Virus (HBV), Hepatitis C Virus (HCV) and Hepatitis E virus (HEV). Hepatitis A and E viruses enter the body through contaminated food and water and cause short-term (acute) infections that can resolve and improve on their own. Hepatitis B and C are transmitted through blood and cause long-term (chronic) infections that can hamper a patient’s life. Interferon injections (common to treatment of both kinds of infections) along with oral drugs like ribavirin capsules (hepatitis C specific) are initiated if the viral load in blood is greater than a certain value. Some anti-HIV drugs are also used in viral hepatitis. Side effects on interferon injections include thyroid abnormalities, flu-like symptoms, tremors, depression and fall in blood pressure.
• Anti-HIV drugs: Anti-HIV or antiretroviral drugs are used in antiretroviral therapy (ART) regimes designed to combat AIDS in HIV-infected individuals. Three main classes of drugs are used to administer a daily triple-drug treatment plan. This therapy is continued lifelong but the combination of drugs may be changed if the viral load is not being effectively controlled. Usually, as the first line of treatment, a combination of two nucleoside reverse transcriptase inhibitors (NRTIs), like Zidovudine and Lamivudine, is given along with a non-nucleoside reverse transcriptase inhibitor (NNRTI) - either Nevirapine or Efavirenz. If the virus concentration isn’t reduced, one of the NRTIs can be switched with another and a protease inhibitor medicine, like Lopinavir with Ritonavir, is started.

Viruses may invade the human body’s cells and cause infection and disease. To check their replication, antivirals are used. However, prevention is always better than cure. By preemptively introducing small doses of inactivated or attenuated viruses through vaccines, immunity against subsequent deadly infections by these viruses is generated. Vaccination against common viral diseases like polio, measles, rubella, hepatitis, influenza, chickenpox or shingles amongst others is advocated and available.

Influenza: While most cases of flu resolve with symptomatic treatment and rest, it becomes necessary to medicate in some instances. These include:

• Children aged 2 or younger
• Elderly aged 65 or older
• Pregnant women
• Postpartum women ( 2 weeks after delivery of baby)
• Immunocompromised individuals (those who have cancer or receiving treatment for it, HIV positive, etc)
• Individuals with chronic diseases (like cardiac problems, etc)
• Individuals aged under 19 and receiving long-term aspirin therapy
• Morbidly obese individuals
• Individuals staying in old-age homes or nursing homes

Viral hepatitis: While not all people with chronic viral hepatitis (hepatitis B and hepatitis C) develop liver disease and need drugs, liver cancer (Hepatocellular carcinoma / Hepatoma) is a real and fatal possibility. Antiviral medicines might be initiated if:

• Liver function test reports show liver enzyme and ALT (alanine aminotransferase) levels to be elevated
• Viral HBV DNA in the blood is higher than the permissible limit
• Liver biopsy or fibroscan shows signs of cirrhosis (change in liver disease)
• Prophylactically (as a precautionary measure) in patients undergoing viral hepatitis related liver transplant (to prevent recurrence)
• Pregnant women in their last trimester with high blood viral concentration (to prevent any transmission to the baby)

HIV-AIDS: HIV treatment should be started as soon as the diagnosis is made. Regardless of age, health status and viral load in blood, all patients need lifelong daily combination drug treatment (combination antiretroviral therapy or cART). The HIV virus integrates its genetic material with that od the human host's cells. Therefore, it cannot be eradicated and the best strategy would be to prevent the breakdown of the immune system or AIDS and to suppress the viral load with the use of medications.

During pregnancy, a woman’s immune, cardiac and respiratory systems undergo changes to provide better support for the growing baby. This may leave the mother’s immunity weakened and she may become more vulnerable to viral infections, such as influenza. Therefore, immediate initiation of flu treatment (within 48 hours) is recommended if infection caused by influenza virus is suspected. As a woman’s immunity does not fully recover within the first two weeks of delivery (postpartum period), this is also a critical time that requires many expedited treatment measures. Oseltamivir tablets and zanamivir inhalation powder are considered safe for use in pregnancy and are widely prescribed.

Mothers who are hepatitis B positive and have a very high viral load should be given antiviral treatment in the third trimester to prevent giving the infection to the baby. If they are already receiving therapy, they should be switched to tenofovir, which is the drug of choice to treat chronic viral hepatitis in pregnancy. The baby should be vaccinated with hepatitis B vaccine within 12 hours of birth along with Hepatitis B immunoglobulins (HBIG). In the six months following delivery, the hepatitis B virus may reactivate in the mother. Therefore, liver function tests should be repeated regularly to check liver enzyme levels.