Antiviral drugs

Encyclopedia of Medicine, Apr 06, 2001 by Nancy Ross-Flanigan

Antiviral drugs are medicines that cure or control virus infections.

Antivirals are used to treat infections caused by viruses. Several different drugs in the antiviral family exist, 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 the genitals, 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 people whose 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. These drugs will not work for common colds, other types of flu, or other virus infections, however.

Still another class of drugs, antiretroviral drugs, targets a specific type of virus called a retrovirus. Human immunodeficiency virus (HIV), the virus that causes AIDS, is a retrovirus. Antiretroviral drugs are described in another section.

Viruses are tiny structures too small to see with a regular microscope. Although scientists have known about viruses since the late 1800s, the invention of the electron microscope in the 1940s made it possible to see what viruses look like. The powerful electron microscope revealed that a virus is nothing more than a core of genetic material (RNA or DNA), wrapped in a protective protein coat. But its simple structure is deceptive. Viruses are among medicine's most formidable foes, causing a wide range of diseases that are difficult to treat.

Part of the problem has to do with the way viruses cause infections. These tiny agents of disease are not considered living things, because they cannot reproduce on their own. They must invade the cells of other living things and take over the cells' machinery to make more copies of themselves. Once inside their hosts' cells, viruses reproduce wildly, spread through the body and cause illness. Some illnesses caused by viruses come and go -- common colds, flu, measles, mumps, and chicken pox, for example. 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. Examples of antiviral drugs are acyclovir (Zovirax), amantadine (Symmetrel, Symadine), famciclovir (Famvir), ganciclovir (Cytovene), rimantadine (Flumadine), and valacyclovir (Valtrex)

The recommended dosage depends on the type of antiviral drug and the kind of infection for which 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. Do not stop taking the drug just because symptoms begin to improve, and do not miss 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.

Symptoms should begin to improve within a few days of beginning to take this medicine. If they do not, or if they get worse, check with the physician who prescribed the medicine.

Some people feel dizzy, confused, or lightheaded when using these drugs. The medicine may also cause blurred vision and problems with concentration. For these reasons, anyone who takes these drugs should not drive, use machines or do anything else that might be dangerous until they have found out how the drugs affect them.