What is Antiviral Therapy?
What Is Antiviral Therapy?
Antiviral therapy means treating viral infections like HIV with drugs. The drugs do not kill the virus. However, they slow down the growth of the virus. When the virus is slowed down, so is HIV disease. Because HIV is a retrovirus, these drugs are sometimes called antiretroviral therapy.
What Is The HIV Life Cycle?
There are several steps in the HIV Life Cycle..
1. Free virus circulates in the bloodstream.
2. HIV attaches to a cell.
3. HIV empties its contents into the cell (infects the cell).
4. The HIV genetic code (RNA) is changed into DNA by the reverse transcriptase enzyme.
5. The HIV DNA is built into the infected cell's DNA by the integrase enzyme.
6. When the infected cell reproduces, it activates the HIV DNA, which makes the raw material for new HIV viruses.
7. Packets of material for a new virus come together.
8. The immature virus pushes out of the infected cell in a process called "budding."
9. The immature virus breaks free of the infected cell.
10. The new virus matures: raw materials are cut by the protease enzyme and assembled into a functioning virus.
What Are The Antiviral Drugs?
Each type, or "class", of antiviral drugs attacks HIV in a different way. The first class of anti-HIV drugs was the nucleoside reverse transcriptase inhibitors, also called "nukes". These drugs work by blocking Step 4, where the HIV genetic material is converted from RNA into DNA. Approved drugs in this class include:
AZT (ZDV, zidovudine, CAMOZUDINE®)
ddI
(didanosine)
ddC
(zalcitabine)
d4T (stavudine)
3TC (lamivudine, CAMUDINE®)
Abacavir
AZT/3TC combination, CAMAL-Z®
AZT/3TC/d4T combination, CAMLANS®
Emtricitabine (FTC)
Another class of drugs blocks the same step of the life cycle, but in a different way. This class is the non-nucleoside reverse transcriptase inhibitors, or NNRTIs. Three NNRTIs have been approved:
Nevirapine (NVP)
Delavirdine
(DLV)
Efavirenz (EFV, CAMVERENZ®)
The third class of antiviral drugs block Step 7, where the raw material for new HIV virus is cut into specific pieces. Nine protease inhibitors have been approved
Saquinavir (SQV)
Indinavir
(IDV)
Ritonavir (RTV)
Nelfinavir
(NFV)
Amprenavir (APV)
Lopinavir (LPV)
Atazanavir (TAZ)
Fosamprenavir (908)
The newest class of antiviral drugs includes fusion and attachment inhibitors. They prevent HIV from attaching to a cell by blocking Step 2 of the life cycle. One fusion inhibitor has been approved:
Enfuvirtide (T-20)
How Are The Drugs Used?
When HIV multiplies, most of the new copies are mutations: they are slightly different from the original virus. Some mutations keep multiplying even when you are taking an antiviral drug. When this happens, the drug will stop working. This is called "developing resistance" to the drug.
If only one antiviral drug is used, it is easy for the virus to develop resistance. But if two drugs are used, a successful mutant would have to "get around" both drugs at the same time. And if three drugs are used, especially if they attack HIV at different points in its life cycle, it's very hard for a mutation to show up that can resist all three drugs at the same time.
Using a triple-drug combination means that it takes much longer for resistance to develop. For this reason, using just one antiviral drug (monotherapy) is not recommended.
Can These Drugs Cure Aids?
A blood test called the "viral
load" measures the amount of HIV virus in your bloodstream. People with lower viral loads stay healthier longer.
Some people's viral load is so low that it is "undetectable" by the viral load test. This does not mean that the entire virus is gone. Researchers used to believe that antiviral therapy could eventually kill off the entire HIV virus in the body. Now this seems unlikely. The drugs do not "cure" AIDS. However, they make it possible for people with AIDS to live a long time.
When Do You Start?
There is not a clear answer to this question. Most doctors will consider three things: 1) your
viral load; 2) your T-cell
count; and 3) any symptoms you've had. Antiviral therapy is usually started if your viral load is over 55,000, if your T-cell count is below 350, or if you’ve had any symptoms of HIV disease. This is an important decision you should discuss with your doctor.
Which Drugs Do You Use?
Each antiviral drug has side
effects. Some are serious. Some combinations of drugs are easier to tolerate than others, and some seem to work better than others. Each person is different, and you and your doctor will have to decide which drugs to use.
The viral load test is now being used to see if antiviral drugs are working. If the viral load does not go down, or if it goes down but comes back up, it might be time to change antiviral drugs.
What's Next?
New drugs are being developed in all four of the existing classes. Researchers are also trying to develop new types of drugs, such as drugs that will block other steps in the
HIV life cycle, and drugs that will strengthen the body's immune defenses.
