Antiretroviral therapies can target any one of a number of processes required for the replication of a retrovirus. There are six classes of retrovirals:
- Nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs)
- Non-nucleoside reverse transcriptase inhibitors (NNRTIs)
- Protease inhibitors (PIs), which interfere with the modification of viral proteins that is required for the formation of new HIV virus particles
- Fusion inhibitors
- CCR5 antagonists
- Integrase inhibitors, which prevent integration of the viral DNA into the DNA of the infected cell
One of the most common targets is the enzyme known as reverse transcriptase, which is responsible for transforming the retrovirus's RNA into DNA so that it can be incorporated into the infected cell's genome. Drugs that target this enzyme are known as reverse transcriptase inhibitors.
Reverse transcriptase inhibitors fall into two categories: nucleoside reverse transcriptase inhibitors (also called nucleotide reverse transcriptase inhibitors), or NRTIs, and non-nucleoside reverse transcriptase inhibitors, or NNRTIs. NRTIs are "fake" versions of the elements that make up DNA. They are designed to be integrated into the copied viral genome to block further elongation. In contrast, NNRTIs affect the action of reverse transcriptase directly.