Drug treatment of human immunodeficiency virus (hiv) infection

[Ernesto]

Antiretroviral drugs used to treat human immunodeficiency virus (HIV) infection aim to do the following:

Reduce the amount of HIV RNA (viral load) in the blood to an undetectable amount
Restore the CD4 count to a normal level

Several classes of antiretroviral drugs are used together to treat HIV infection. These drugs block HIV from entering human cells or block the activity of one of the enzymes HIV needs to replicate inside human cells and/or integrate its genetic material into human DNA.
The drugs are grouped into classes based on how they act against HIV:

Reverse transcriptase inhibitors prevent HIV reverse transcriptase from converting HIV RNA into DNA. There are three types of these drugs: nucleoside, nucleotide, and non-nucleoside.
Protease inhibitors prevent protease from activating certain proteins inside newly produced viruses. The result is immature, defective HIV that does not infect new cells.
Entry (fusion) inhibitors prevent HIV from entering cells. To enter a human cell, HIV must bind to a CD4 receptor and one other receptor, such as the CCR-5 receptor. One type of entry inhibitor, CCR-5 inhibitors, blocks the CCR-5 receptor, preventing HIV from entering human cells.
Post-attachment inhibitors also prevent HIV from entering cells but in a different way from fusion inhibitors. These are used mainly for HIV infection that is resistant to several other drugs.
Integrase inhibitors prevent HIV DNA from being integrated into human DNA.

These drugs prevent HIV from replicating in cells and dramatically reduce the amount of HIV in the blood over a few days to weeks. If replication is sufficiently slowed, the destruction of CD4 lymphocytes by HIV is decreased and the CD4 count begins to increase. As a result, much of the damage to the immune system caused by HIV can be reversed. Doctors can detect this reversal by measuring the CD4 count, which begins to return toward normal levels over weeks to months. The CD4 count continues to increase for several years but at a slower rate.
Early diagnosis of HIV infection is important because it enables doctors to identify people with HIV infection before their CD4 cell count decreases too much. The sooner people start taking antiretroviral drugs, the more quickly their CD4 count is likely to increase and the higher the count is likely to become.
HIV invariably develops resistance to any of these drugs if they are used alone. Resistance develops after a few days to several months of use, depending on the drug and the virus. HIV becomes resistant to drugs because of mutations that occur when it replicates.
Treatment is most effective when two or more drugs are given in combination. These combinations of drugs are often referred to as combination antiretroviral therapy (cART). cART is used because

Combinations are more powerful than single drugs in reducing the amount of HIV in the blood.
Combinations help prevent the development of drug resistance.
Some HIV drugs (such as ritonavir ) boost the blood levels of other HIV drugs (including most protease inhibitors) by slowing their removal from the body and thus increase their effectiveness.

cART can increase the CD4 count in HIV-infected people, thus strengthening their immune system and extending their life.