Antiretroviral drugs target human immunodeficiency virus 1 to slow the progression of the HIV to acquired immunodeficiency syndrome, or AIDS. As of 2010, the World Health Organization estimates that among the 33.4 million people living with HIV/AIDS around the world, 9.5 million people are in need of antiretroviral drugs. By the end of 2008, just over 4 million people in low- to middle-income countries were receiving antiretroviral therapies to treat HIV.
Classes of Antiretroviral Drugs
Antiretroviral drugs are used in combination. As of May 2010, there are 5 different classes of antiretroviral drugs which use different mechanisms to inhibit HIV. One class of antiretroviral drugs prevents the virus from binding to and entering immune cells; drugs in this class are called fusion or entry inhibitors. Three classes of antiretroviral drugs can stop the virus from replicating within human immune cells. Nucleoside/nucleotide reverse transcriptase inhibitors target the actions of a specific HIV protein that are essential for the virus to replicate within the cell. Non-nucleoside reverse transcriptase inhibitors also stop HIV from replicating within cells by inhibiting the same HIV protein. Protease inhibitors are another class of antiretrovirals that limit HIV replication by targeting a specific HIV protein. The fifth class of antiretrovirals stop HIV genetic material from integrating into the human immune cells, again limiting the virus' ability to replicate; this class of antiretrovirals are called integrase inhibitors.
Access to Antiretroviral Combinations
Antiretrovirals for treating HIV infection have been available since 1987, and new antiretroviral drugs continue to be developed. However, cheaper generic versions of some antiretroviral drugs are available. For example, azidothymidine, or AZT, is a nucleoside/nucleotide reverse transcriptase inhibitors and the first antiretroviral drug that was licensed for use in 1987; the license for AZT has expired and generic versions are available around the world. According to AVERT, an international HIV/AIDS charity, there are more than 20 antiretroviral drugs approved for use in Europe and the United State, but not all of these drugs are available in every country.
Combinations of Antiretroviral Drugs
Typically antiretrovirals are used in combinations of three or more drugs, sometimes including drugs from more than one class. Most commonly included in combinations are antiretroviral drugs that inhibit viral replication. Combinations of antiretroviral therapies use different mechanisms to target HIV and mean more efficacious treatments because antiretrovirals are able to mount an attack against the virus on multiple fronts. HIV is a virus that rapidly changes its genetic material during replication. While rapid genetic changes continue to occur during antiretroviral treatment, the use of combination therapies limits the opportunities for HIV to develop mutations that favor specific resistance to individual antiretroviral drugs, AVERT's website notes.
