For a patient with HIV and lymphoma on Biktarvy (bictegravir/emtricitabine/tenofovir alafenamide) and Pifeltro (ivosidenib) for 90 days, with a CD4 count of 163 cells/µL, CD4% of 16.3%, and an HIV viral load of 320 copies/mL, who recently received trimethoprim‑sulfamethoxazole (Bactrim) and acyclovir prophylaxis, should I continue or restart Pneumocystis jirovecii pneumonia prophylaxis with trimethoprim‑sulfamethoxazole, and are there any additional recommendations at this time?

Continue Bactrim Prophylaxis and Address Virologic Failure

You should absolutely continue trimethoprim-sulfamethoxazole (Bactrim) prophylaxis for PCP given the CD4 count of 163 cells/µL, and more urgently, you need to address the detectable viral load of 320 copies/mL after 90 days on Biktarvy, which indicates treatment failure. 1

PCP Prophylaxis - Clear Indication

Your patient meets established criteria for PCP prophylaxis:

• CD4 count <200 cells/µL (163 cells/µL) is an absolute indication for primary prophylaxis 1
• The guideline recommendation is strength AI (highest level) for initiating chemoprophylaxis at CD4 <200 cells/µL 1

Trimethoprim-sulfamethoxazole remains the preferred agent (AI recommendation):

• One double-strength tablet daily is the preferred regimen 1
• One single-strength tablet daily is also effective and may be better tolerated 1
• This provides cross-protection against toxoplasmosis and common respiratory bacterial infections 1, 2

The patient should continue Bactrim indefinitely until CD4 count rises above 200 cells/µL for at least 3 months in the setting of viral suppression.

Critical Issue: Virologic Failure

The detectable viral load of 320 copies/mL after 90 days on Biktarvy is concerning and requires immediate attention. Expected response to effective antiretroviral therapy should show viral suppression (HIV RNA <50 copies/mL) by 12-24 weeks in most patients.

Assess for Treatment Failure Causes:

1. Medication adherence - Most common cause of virologic failure

   • Review pill-taking patterns, missed doses, timing
   • Assess barriers to adherence (side effects, pill burden, psychosocial factors)

2. Drug interactions - Critical concern with Pifeltro (doravirine)

   • Review the drug label: Pifeltro has multiple contraindicated interactions that reduce doravirine levels 3
   • Verify no concurrent use of CYP3A inducers (rifampin, rifapentine, carbamazepine, phenytoin, St. John's wort, etc.) 3
   • Important caveat: The question mentions "Pifeltro" but this is doravirine, an NNRTI. Using Pifeltro with Biktarvy (which contains the INSTI bictegravir) is unusual - verify this is not a medication error or documentation issue

3. Baseline resistance testing - Should have been performed before starting therapy

   • If not done, obtain genotypic resistance testing now while on failing regimen
   • This will guide selection of next regimen

4. Lymphoma treatment effects - Chemotherapy can affect immune reconstitution and potentially adherence

Immediate Actions:

• Obtain HIV genotypic resistance testing immediately (while patient is still on current regimen)
• Comprehensive medication reconciliation - confirm all medications, supplements, herbals
• Adherence counseling and assessment
• Consider therapeutic drug monitoring if available
• Do NOT stop antiretroviral therapy while investigating

Additional Prophylaxis Considerations

Given CD4 163 cells/µL:

• Acyclovir prophylaxis - Already appropriately prescribed for HSV suppression
• Consider MAC prophylaxis if CD4 drops below 50 cells/µL (azithromycin 1200 mg weekly or clarithromycin 500 mg twice daily) 2
• Toxoplasmosis prophylaxis - Already covered by daily double-strength TMP-SMX 1

Common Pitfalls to Avoid

1. Do not discontinue PCP prophylaxis based on viral suppression criteria alone when CD4 <200 cells/µL - while some data suggest safety with viral suppression 4, this patient has detectable viremia, making continuation mandatory
2. Do not assume the current regimen will eventually work - 320 copies/mL at 90 days suggests failure, not delayed response
3. Do not delay resistance testing - must be done while on failing regimen to detect relevant mutations
4. Verify the medication regimen - concurrent use of Biktarvy and Pifeltro is atypical and may represent prescribing error

Monitoring Plan

• Repeat HIV viral load in 4 weeks after addressing adherence/interactions
• Recheck CD4 count with viral load
• Continue Bactrim prophylaxis throughout
• Plan regimen change based on resistance testing results if adherence/interactions are not the issue