ART Management of Virologically Suppressed HIV Patients

1. Core Principle: Suppression Must Be Maintained Indefinitely

Harrison's Principles of Internal Medicine, 22E (2025) — patients randomized to intermittent therapy had more serious adverse events than those on continuous therapy, demonstrating that some "non-AIDS-defining" events such as MI and stroke are linked to HIV replication.

2. Preferred Maintenance Regimens (DHHS-Aligned)

A. Standard Triple Therapy (preferred first-line backbone)

B. Simplified / Streamlined Oral Regimens (switch strategies for suppressed patients)

2-Drug Regimens (INI + NNRTI or NRTI)

2-drug switch meta-analysis (PMID: 41189136, 2025): Triple-to-dual switches with integrase inhibitors maintained virologic suppression comparably to triple therapy with a favorable safety profile in suppressed patients.

C. Long-Acting Injectable ART (paradigm shift for virologically suppressed patients)

• Eliminates daily pill burden → dramatically improves adherence and quality of life
• Removes stigma of daily visible pill-taking

• Missed injection > 7 days: resume oral therapy until next scheduled injection
• HBV co-infection: contraindicated for switch from tenofovir-containing regimen — risk of HBV rebound and acute liver injury
• Prior INSTI resistance (especially subtype A1/A6 viruses: higher CAB failure rates)
• Interaction with potent CYP/UGT inducers: rifamycins, carbamazepine, phenytoin, St. John's wort — all contraindicated

Systematic review/NMA (PMID: 40426337, 2025): CAB+RPV injectable had comparable virologic efficacy and resistance-associated mutation rates vs. oral single-tablet INI-based regimens in suppressed patients.

D. Lenacapavir (Sunlenca) — Emerging Role

• Capsid inhibitor — novel mechanism (interferes with nuclear import, assembly, and capsid core formation)
• Currently licensed for heavily treatment-experienced, multidrug-resistant patients; not a first-choice switch agent
• SC injection every 6 months after oral/SC loading — extremely long-acting
• Being actively studied in combination with islatravir for broader maintenance use

3. When to Switch a Suppressed Patient's Regimen

• Historical resistance testing
• Subtype (subtype A1/A6 increases CAB/RPV failure risk)
• HBV co-infection status
• CD4 nadir and current count
• Prior treatment failures

4. Monitoring in Virologically Suppressed Patients

5. Special Situations

Summary

• Harrison's Principles of Internal Medicine, 22E (2025) — DHHS principles of ART, integrase inhibitors, CAB/RPV
• Goodman & Gilman's Pharmacological Basis of Therapeutics — LA cabotegravir and rilpivirine pharmacology
• Katzung's Basic and Clinical Pharmacology, 16th Ed. — INSTI class, bictegravir, cabotegravir
• Triple-to-dual INSTI switch meta-analysis (PMID 41189136, 2025)
• CAB+RPV vs. oral STR network meta-analysis (PMID 40426337, 2025)

Drug Classes of ART Agents in Virologically Suppressed HIV Management

Integrase Strand Transfer Inhibitors (INSTIs)

Mechanism: Block HIV integrase enzyme → prevent integration of proviral DNA into host cell genome

Nucleoside/Nucleotide Reverse Transcriptase Inhibitors (NRTIs/NtRTIs)

Mechanism: Phosphorylated to active form → competitive inhibition of reverse transcriptase → chain termination; active against HIV-1, HIV-2, and some HBV

Non-Nucleoside Reverse Transcriptase Inhibitors (NNRTIs)

Mechanism: Non-competitive, direct binding to RT allosteric site → conformational change → inhibits RT; HIV-1 specific (NOT active against HIV-2)

Protease Inhibitors (PIs)

Mechanism: Inhibit HIV aspartyl protease → prevent cleavage of gag-pol polyprotein → immature, non-infectious virions

Entry Inhibitors

Mechanism: Block HIV attachment, co-receptor binding, or membrane fusion

Capsid Inhibitor

Mechanism: Binds p24 capsid hexamer interface → disrupts nuclear import, viral assembly, and capsid core formation (multi-step inhibition)

Pharmacokinetic Enhancers ("Boosters")

Not antiretrovirals themselves — inhibit CYP3A4/P-gp to increase plasma concentrations of co-administered drugs

Quick Reference: Common Regimens by Class Combination

Intermediate vs. Delayed (Obligate) Chain Termination by NRTIs

The Normal DNA Elongation Process (Background)

1. Adding a deoxynucleoside triphosphate (dNTP) to the 3′-OH of the growing chain
2. This forms a 3′–5′ phosphodiester bond
3. The free 3′-OH on the newly added nucleotide becomes the attachment point for the next incoming dNTP
4. Elongation continues

The key requirement for chain extension: the last incorporated nucleotide must have a free 3′-OH group

Obligate (Immediate / True) Chain Termination

Definition

Mechanism

...DNA chain—[NRTI-TP incorporated]
                    ↑
              No 3'-OH exists
              → Next dNTP CANNOT bind
              → IMMEDIATE termination

Examples

Delayed (Non-Obligate / Conditional) Chain Termination

Definition

Mechanism

...DNA chain—[NRTI-TP incorporated (has 3'-OH)]
                    ↓
         RT adds 1–3 more nucleotides
                    ↓
         Steric/conformational distortion
         accumulates → RT stalls → termination

Examples

Tenofovir is actually a nucleotide analogue (no sugar ring at all — acyclic). The lack of a ribose ring means RT can continue briefly but then stalls due to chain geometry misalignment.

Why Intermediate (Delayed) Chain Termination Alone is NOT Sufficient

1. Incomplete Block → Partial Viral DNA Synthesis

• Be used as a template for further synthesis by another RT molecule
• Undergo repair by cellular or viral mechanisms
• Act as a substrate for integration if long enough

2. Excision Repair by RT Itself (Pyrophosphorolysis)

• Obligate terminators (no 3′-OH) → once incorporated, the chain is a dead-end — excision is the only resistance mechanism, requiring specific TAMs (thymidine analogue mutations like M41L, D67N, K70R)
• Delayed terminators (have 3′-OH) → the subsequent bases incorporated after the analogue make the template longer and actually easier for RT to excise the upstream analogue using its pyrophosphorolysis activity → lower barrier to resistance

3. Lower Selective Pressure = Faster Resistance Emergence

4. Why Two NRTIs Are Always Paired (and Combined with a Third Agent)

• A typical backbone pairs one obligate + one delayed terminator (e.g., TDF [delayed] + FTC [obligate]) to block RT at multiple positions
• A third agent from a different class (INSTI, NNRTI, or PI) is added to prevent the small amount of elongation escaping one NRTI pair from producing viable virions

Katzung's Basic & Clinical Pharmacology: "The NRTIs act by competitive inhibition of HIV-1 reverse transcriptase; incorporation into the growing viral DNA chain causes chain termination due to inhibition of binding with the incoming nucleotide."

Summary Table

Bottom Line

1. Partial DNA synthesis still occurs → possible template re-use
2. RT's pyrophosphorolysis more easily removes non-obligate terminators
3. Resistance evolves faster with incomplete block
4. Combination therapy (dual NRTI backbone + third agent) is required to achieve the multi-layered suppression needed to prevent resistance and achieve durable viral suppression below 50 copies/mL