Highly active antiretroviral therapy (HAART)
Also known as: haart, combination antiretroviral therapy, art
Highly active antiretroviral therapy is the treatment of HIV with a combination of at least three antiretroviral drugs from two or more classes taken together. Combining agents suppresses viral replication far more durably than any single drug and sharply reduces the emergence of resistance.
HIV replicates rapidly and its reverse transcriptase copies RNA without proofreading, so single-drug therapy selects for resistant virus within weeks. Highly active antiretroviral therapy answers that problem by attacking several steps of the viral life cycle at once, typically with three or more agents drawn from at least two drug classes. The term dates from the mid-1990s; current practice more often calls the same approach simply antiretroviral therapy (ART), since combination treatment is now the only standard.
The major drug classes each block a different step. Nucleoside and nucleotide reverse transcriptase inhibitors (NRTIs) are chain terminators that stop viral DNA synthesis. Non-nucleoside reverse transcriptase inhibitors (NNRTIs) bind reverse transcriptase allosterically to inactivate it. Integrase strand transfer inhibitors prevent viral DNA from being inserted into the host genome. Protease inhibitors block cleavage of viral polyproteins, so new virions are immature and noninfectious. Entry inhibitors, including CCR5 antagonists and fusion inhibitors, keep the virus out of the cell entirely. A common regimen pairs a backbone of two NRTIs with a third agent from another class, often as a single-tablet fixed-dose combination.
Effective therapy suppresses viral load, allows the CD4+ T cell count to recover, prevents progression to AIDS and opportunistic infection, and — because durable suppression makes sexual transmission negligible — reduces spread. Treatment is lifelong, since interruption allows rebound from latent reservoirs, so adherence is central. Class-specific toxicities include mitochondrial effects and lactic acidosis with older NRTIs, rash and hepatotoxicity with NNRTIs, and metabolic effects such as lipodystrophy and hyperlipidemia with protease inhibitors. Because several agents are substrates, inhibitors, or inducers of cytochrome P450 enzymes — ritonavir is used deliberately as a pharmacokinetic booster for this reason — interaction screening is routine at dispensing.
USMLE Step 1 tests the mechanism and characteristic toxicity of each class within antimicrobial pharmacology, and the PTCE covers antiretrovirals among antivirals — expect to match drugs to their class, recognize combination products, and flag interactions.
Key takeaways
- HAART combines at least three antiretroviral drugs from two or more classes to suppress HIV replication.
- Combination therapy is used because single-agent treatment rapidly selects for resistant virus.
- Classes include NRTIs, NNRTIs, integrase strand transfer inhibitors, protease inhibitors, and entry inhibitors.
- Successful therapy suppresses viral load, restores CD4+ counts, and prevents progression and transmission.
- Therapy is lifelong; adherence, class-specific toxicities, and cytochrome P450 drug interactions are ongoing management concerns.