Antiviral drugs

Antiviral drugs are medicines that cure or control virus infections. There are several different drugs in the antiviral family, and each is used for specific kinds of viral infections. For example, acyclovir (Zovirax) is used to treat chickenpox, shingles, and the symptoms of herpes virus infections of thegenitals, lips, mouth, skin, and brain. The medicine does not cure the infections, but it relieves the discomfort and speeds healing of sores, when they are present. Similarly, valacyclovir (Valtrex) and famciclovir (Famvir) can also be used to relieve the symptoms of shingles. Another antiviral, ganciclovir (Cytovene) is prescribed for cytomegalovirus (CMV) eye infections in peoplewhose immune systems are weakened. Ganciclovir does not cure the CMV infection, but it may keep the symptoms from getting worse. Ganciclovir may also help prevent CMV infections in people who are going to be given drugs or treatments that will weaken their immune systems, such as organ or bone marrow transplant patients.

Other types of antiviral drugs, such as amantadine (Symmetrel) and rimantadine (Flumadine) are used to prevent or treat certain kinds of influenza (flu).They are given either alone or in combination with flu shots. Still another class of drugs, antiretroviral drugs, targets a specific type of virus calleda retrovirus. Human immunodeficiency virus (HIV), the virus that causes AIDS,is a retrovirus.

Viruses are tiny structures that are too small to be seen with a regular microscope. The powerful electron microscope invented in the 1940s revealed thata virus is nothing more than a core of genetic material (RNA or DNA), wrappedin a protective protein coat. These tiny agents of disease are not considered living things, because they cannot reproduce on their own. They must invadethe cells of other living things and take over the cells' machinery to makemore copies of themselves. Once inside their hosts' cells, viruses reproducewildly, spread through the body and cause illness. Some illnesses caused by viruses come and go -- common colds, flu, measles, mumps, and chicken pox, forexample. Others, such as cytomegalovirus and Epstein-Barr virus, linger in the body for life.

Developing antiviral medicines has been difficult, because most drugs that kill viruses also damage the host's cells, where the viruses hide. However, since the 1980s, when the virus that causes AIDS began to receive attention, medical researchers have focused on the problem of treating viral infections, and encouraging progress has been made. Rather than killing the viruses, antiviral drugs block steps in the process through which viruses reproduce. Some may also stimulate the immune system so that the body can fight the viruses itself.

Antiviral drugs are available only with a physician's prescription and are sold in capsule, tablet, liquid, ointment, and injectable forms. The recommended dosage depends on the type of antiviral drug and the kind of infection forwhich it is being used. Dosage may be different for different people. Check with the physician who prescribed the drug or the pharmacist who filled the prescription for the correct dosage.

Some antiviral drugs work best when they are at constant levels in the blood.To help keep levels constant, take the medicine in doses spaced evenly through the day and night. Do not miss any doses. To make sure the infection clears up completely, take this medicine for as long as it has been prescribed. Donot stop taking the drug just because symptoms begin to improve, and do notmiss any doses. Do not to take the medicine for longer than the physician orders. When taken by mouth, these medicines should be taken with a full glass of water. Some must be taken with food. Check package directions or ask the physician or pharmacist for instructions on how to take the medicine.

When taking an antiviral drug to prevent flu, start taking the medicine before, or as soon as possible after, being exposed to people who have the flu. When taking an antiviral medicine for chickenpox, shingles, or herpes infection, start taking the medicine as soon as possible after the symptoms appear. The medicine may not be as effective if too much time passes. Patients who aretaking an antiviral drug for herpes should keep in mind that the medicine will not prevent them from spreading the infection to other people. They must still take precautions to avoid passing the virus through sexual contact.

People with certain other medical conditions or who are taking certain othermedicines can have problems if they take antiviral drugs. Before taking thesedrugs, be sure to let the physician know about any of these conditions. Drinking alcoholic beverages while taking certain antiviral drugs may increase the chance of side effects. Anyone who takes these drugs should check with a physician before drinking alcohol or taking medicines that contain alcohol. Anyone who has had unusual reactions to antiviral drugs in the past should let his or her physician know before taking the drugs again. The physician shouldalso be told about any allergies to foods, dyes, preservatives, or other substances.

Women who are pregnant or who may become pregnant should check with their physicians before using antiviral drugs. Women who are breastfeeding should alsocheck with their physicians before using any antiviral drug. If the medicineis needed, avoiding breastfeeding while under treatment may be necessary.

Taking antiviral drugs with certain other medicines may affect the way the drugs work or may increase the chance of side effects. Antiviral drugs may alsointeract with a number of other medicines. When this happens, the effects ofone or both of the drugs may change or the risk of side effects may be greater. The most common minor side effects are diarrhea, nausea or vomiting, dizziness, lightheadedness, headache, sleep problems, concentration problems, andirritability or nervousness. These problems usually go away as the body adjusts to the drug and do not require medical treatment unless they do persist or they interfere with normal activities. More serious side effects are possible and if any do occur, check with a physician. Anyone who takes antiviral drugs should let the physician know all other medicines he or she is taking.

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