Which class of HIV medication currently forms the backbone of most first-line regimens because of its potency, tolerability, and high barrier to resistance?
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Clinical Pharmacology · Antiviral Medications
HIV Medications
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HIV medications (antiretroviral therapy, or ART) work by blocking specific steps the virus needs to copy itself inside human cells, and they are always combined so the virus cannot easily escape. Modern regimens, usually built around an integrase inhibitor, achieve durable viral suppression, protect and restore the immune system, and allow people with HIV to live long healthy lives. Adherence is the single biggest determinant of whether the virus stays suppressed or develops resistance. These same drug classes also underpin prevention strategies like pre-exposure prophylaxis and treatment-as-prevention.
The college version
The replication cycle as a map of drug targets
HIV attaches to and enters CD4 T-cells, uses reverse transcriptase to convert its RNA into DNA, uses integrase to splice that DNA into the host genome, and uses protease to cleave viral proteins into mature infectious particles. Each antiretroviral class blocks one of these steps, and because HIV mutates rapidly, no single drug controls it for long. Combination therapy with at least two active drugs from different classes, started as soon as possible after diagnosis, is the standard of care.
Reverse transcriptase inhibitors
Nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs) are faulty DNA building blocks that terminate the growing viral DNA chain. Tenofovir (as alafenamide or disoproxil fumarate) paired with emtricitabine or lamivudine forms the backbone of most regimens. Abacavir is effective but requires HLA-B*5701 screening before the first dose, because carriers of this allele can develop a severe, potentially fatal hypersensitivity reaction with fever, rash, and multi-organ symptoms that recurs and worsens with rechallenge. Zidovudine, one of the earliest agents, is historically notable for causing bone marrow suppression and macrocytic anemia and is rarely used today. Non-nucleoside reverse transcriptase inhibitors (NNRTIs) bind a different site on the same enzyme. Efavirenz is associated with vivid dreams, dizziness, and broader neuropsychiatric effects that can limit tolerability; rilpivirine and doravirine are newer options with generally milder side-effect profiles but still carry drug interaction considerations.
Integrase strand transfer inhibitors
Integrase strand transfer inhibitors (INSTIs) — dolutegravir, bictegravir, and raltegravir — block the enzyme that inserts viral DNA into the host chromosome. They are now the backbone of first-line therapy because they combine high potency, excellent tolerability, and a high genetic barrier to resistance, meaning the virus needs multiple mutations to escape them. Single-tablet regimens pairing an INSTI with two NRTIs are common first choices for newly diagnosed patients.
Protease inhibitors
Protease inhibitors, such as darunavir and atazanavir, block the enzyme that cleaves viral polyproteins into functional pieces, producing immature, noninfectious virions. They are almost always pharmacokinetically boosted with low-dose ritonavir or cobicistat, which inhibit the liver enzyme CYP3A4 to raise and sustain drug levels. This boosting is also the source of an enormous drug interaction burden, since CYP3A4 metabolizes many other medications.
Entry inhibitors and other strategies
Entry inhibitors block the virus before it ever gets inside the cell. Maraviroc blocks a co-receptor the virus uses to attach, and requires confirming the virus uses that particular co-receptor before use. Injectable options, including long-acting agents given periodically rather than daily, are expanding, offering an alternative to daily pills for adherence.
Core clinical principles
Adherence directly determines whether resistance develops, since inconsistent dosing allows partially suppressed virus to mutate around drug pressure. The treatment goal is durable suppression of viral replication and reconstitution of immune function. The undetectable equals untransmittable (U=U) principle reflects that sustained viral suppression prevents sexual transmission, reshaping both public health messaging and patient counseling. Immune reconstitution inflammatory syndrome (IRIS) can occur as a recovering immune system mounts an exaggerated inflammatory response to previously subclinical infections after ART begins. Opportunistic infection prophylaxis is used at appropriate points in a person's course to prevent infections the immune system cannot yet fully guard against. Pre-exposure prophylaxis (PrEP) and post-exposure prophylaxis (PEP) use these same drug classes to prevent acquisition of HIV in people at risk, and antiretroviral therapy during pregnancy dramatically reduces perinatal transmission. Drug interactions are pervasive: boosters affect countless CYP3A4 substrates, rifampin induces metabolism and lowers antiretroviral levels, statins may need dose adjustment, acid suppressants can impair absorption of certain agents, and polyvalent cations (calcium, iron, antacids) chelate integrase inhibitors and reduce their absorption.
Eli explains
The same idea, in plain words
Explain it like I’m 10
Imagine a virus is like a tiny machine trying to build copies of itself using your body's factory. It needs several steps to succeed: get inside a cell, copy its instructions, staple those instructions into the cell's own instruction book, and then cut out the finished parts to build new virus machines. HIV medicines are like little wrenches, each one jamming a different step of that machine. Because the virus is sneaky and can change its shape to dodge one wrench, doctors use two or more different wrenches together, so the virus can't dodge all of them at once. When people take their medicine every day like they're supposed to, the wrenches keep jamming the machine so well that the virus can barely be found in the blood at all, and the person stays healthy.
Check yourself
2 review questions from the chapter. Try each one, then open the answer.
A patient on antiretroviral therapy begins missing doses several times a week because of a hectic schedule. Explain, in one or two sentences, the specific consequence this poor adherence risks beyond the virus simply becoming detectable again.
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Missed doses allow the virus to keep replicating under only partial drug pressure
When drug levels dip low and often, the virus can keep multiplying in the presence of the drug, giving it repeated chances to develop mutations that make the medication no longer work, which can compromise future treatment options.
A newly diagnosed patient asks why their doctor wants to start two or three different HIV medications immediately instead of just one. Give a one- or two-sentence explanation grounded in how HIV replicates and mutates.
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Combination therapy prevents the virus from easily evolving around treatment
HIV replicates fast and makes mistakes (mutations) constantly, so a single drug leaves an easy escape route; using two or three drugs from different classes at once means the virus would need multiple simultaneous mutations to survive, which is far less likely to happen.
Quick check
3 questions here. Answers stay hidden until you check.
Before starting abacavir, which screening test must be performed to prevent a potentially fatal reaction?
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Why are protease inhibitors like darunavir typically given with ritonavir or cobicistat?
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