Are there any documented cases of HIV transmission after using Biktarvy (bictegravir, emtricitabine, tenofovir alafenamide) as post-exposure prophylaxis (PEP) at 64 hours post-exposure?

HIV Transmission Risk with Biktarvy PEP at 64 Hours Post-Exposure

There are no documented cases of HIV transmission specifically after using Biktarvy (bictegravir, emtricitabine, tenofovir alafenamide) as post-exposure prophylaxis at 64 hours post-exposure, but PEP is generally not recommended beyond 72 hours due to significantly diminished efficacy.

Timing of PEP Initiation and Efficacy

The timing of PEP initiation is critical for effectiveness:

• PEP should ideally be initiated as soon as possible after exposure, preferably within hours rather than days 1
• Current guidelines recommend initiating PEP within 72 hours of exposure 1
• Animal studies suggest PEP is likely not effective when started later than 24-36 hours post-exposure, though the exact cutoff for humans remains undefined 1

For exposures at 64 hours:

• This falls within the 72-hour window where PEP is still recommended, though efficacy is likely diminished compared to earlier initiation
• The 2005 CDC guidelines state: "animal and human study data demonstrate that nPEP is less likely to prevent HIV transmission when initiated >72 hours after exposure" 1

Biktarvy as PEP

Biktarvy (BIC/FTC/TAF) has several advantages for PEP use:

• The 2025 CDC guidelines list bictegravir/emtricitabine/tenofovir alafenamide as a preferred regimen for nPEP 1
• A 2022 study demonstrated that Biktarvy was safe, well-tolerated, and highly acceptable when used for PEP with a 90.4% completion rate, which was higher than historical PEP regimens 2
• The single-tablet regimen improves adherence compared to multi-pill regimens 2

Risk Assessment for Late PEP Initiation

When considering PEP at 64 hours post-exposure:

• The 2005 CDC guidelines note: "clinicians might consider prescribing nPEP after exposures that confer a serious risk for transmission, even if the exposed person seeks care >72 hours postexposure if, in the clinician's judgment, the diminished potential benefit of nPEP outweighs the potential risk for adverse events from antiretroviral drugs" 1
• Risk factors to consider include:
  • Type of exposure (higher risk for needle-sharing, receptive anal intercourse)
  • Source person's HIV status and viral load
  • Presence of blood or other infectious fluids

Recommendations for PEP at 64 Hours

For someone presenting at 64 hours post-exposure:

1. Perform rapid HIV testing of the exposed individual to confirm they are HIV-negative 1
2. Assess the exposure risk (type of exposure, source person's HIV status if known)
3. Initiate Biktarvy if the exposure represents a substantial risk for HIV transmission
4. Complete the full 28-day course of PEP as recommended 1
5. Conduct follow-up HIV testing at 4-6 weeks and 12 weeks after exposure 1

Important Considerations

• While there are no specific documented cases of transmission with Biktarvy at 64 hours, the absence of such reports doesn't necessarily confirm efficacy at this timepoint
• A 2021 macaque study showed that FTC/TAF plus bictegravir offered greater than 80% per-exposure risk reduction with treatment initiation up to 24 hours post-exposure 3, suggesting potent activity even with delayed initiation
• The risk-benefit ratio is more favorable with newer, more tolerable drugs like Biktarvy compared to older regimens 1

Pitfalls to Avoid

• Don't delay initiation further - every hour matters for PEP efficacy
• Don't assume complete protection - late initiation reduces efficacy, so additional precautions should be taken until follow-up testing confirms HIV-negative status
• Don't discontinue PEP prematurely - complete the full 28-day course even with late initiation
• Don't forget follow-up testing - testing at 4-6 weeks and 12 weeks is essential to confirm effectiveness

For high-risk exposures at 64 hours, initiating Biktarvy is reasonable despite being beyond the optimal window, as some protection is likely better than none when the risk of HIV acquisition is significant.