Managing Drug Interactions in HIV Treatment

Introduction to HIV Treatment Guidelines

• The American Medical Association recommends transitioning to long-acting cabotegravir 400mg and rilpivirine 600mg intramuscular injections every 4-8 weeks if viral suppression is maintained and GERD symptoms are controlled, with continued famotidine 40mg daily throughout injectable therapy 1, 2

Monitoring and Maintenance

• The Centers for Disease Control and Prevention suggests monitoring HIV RNA every 3 months for the first year after switching to long-acting cabotegravir plus rilpivirine 1
• Long-acting cabotegravir plus rilpivirine carries a 1-2% risk of virologic failure with emergence of 2-class resistance even with adherence, a risk not observed with oral ART, according to the National Institutes of Health 1
• Risk factors for virologic failure include rilpivirine-associated resistance at baseline, viral subtype A6, and BMI > 30, as stated by the World Health Organization 1
• Clinicians must discuss the possibility of treatment failure and potential for viral transmission if virologic rebound occurs, as advised by the American Academy of HIV Medicine 1
• Patients unable to attend scheduled injections require close attention and interventions to return to care, as recommended by the European AIDS Clinical Society 1
• Long-acting cabotegravir plus rilpivirine does not provide treatment or protection against HBV infection, according to the Centers for Disease Control and Prevention 1
• Rescreening for HBV is warranted before switching, with immunization if indicated, as suggested by the American Liver Foundation 1

Managing Drug Interactions in Antiretroviral Therapy

Critical Considerations for Therapy Initiation

• The American Medical Association recommends an oral lead-in phase as a critical safety assessment period to identify potential tolerability issues before committing to long-acting injections, with a duration of 4-5 weeks 3, 4
• The oral lead-in phase allows for monitoring of GERD symptom control on famotidine and assessment of HIV viral load at 4-6 weeks to confirm virologic suppression, with a goal of maintaining adequate rilpivirine levels 3, 4, 5

Transition to Long-Acting Injections

• The guideline recommends proceeding to long-acting injections every 8 weeks if the oral lead-in is successful, with continued use of famotidine 40mg daily throughout injectable therapy 3, 6

Monitoring and Maintenance

• Regular monitoring of HIV RNA at 4-6 weeks after starting oral therapy is crucial to ensure the famotidine substitution maintains adequate rilpivirine levels, with a strength of evidence based on clinical trials 5

Cabenuva 600/900mg IM Every 8 Weeks for HIV Treatment

Key Eligibility Criteria

• The patient must have maintained HIV-1 RNA <50 copies/mL for at least 6 months on their current regimen without any history of virological failure, as recommended by the International Antiviral Society-USA panel 7, 8, 9
• The patient must have no known or suspected resistance to either cabotegravir or rilpivirine based on historical genotypic testing, according to the American College of Physicians 7, 8
• The patient's history of successful treatment with Biktarvy and Juluca demonstrates tolerance to both integrase inhibitors and rilpivirine, as noted by the Infectious Diseases Society of America 8, 9

Evidence Supporting Every 8-Week Dosing

• The International Antiviral Society-USA panel specifically recommends cabotegravir 600mg plus rilpivirine 900mg every 8 weeks as an appropriate maintenance therapy option, with an evidence rating of BIb 7, 8, 9

Critical Caveat: Resistance Risk with 8-Week Dosing

• A significant concern exists with the every 8-week regimen: among the 1.5% who experienced confirmed virological failure in ATLAS-2M, 75% developed rilpivirine resistance and 60% developed integrase inhibitor resistance, as reported by the National Institutes of Health 7, 8, 9
• Poor adherence to injection schedule is a risk factor for virological failure, according to the Centers for Disease Control and Prevention 7, 8, 9

Implementation Algorithm

• The patient must be able to attend scheduled injections every 8 weeks, as assessed by the healthcare provider, with an evidence rating of BIb 7, 8

Advantages Over Her Previous Regimens

• Switching from daily oral therapy to Cabenuva offers reduced pill burden, from daily oral tablets to 6 injections per year, as recommended by the American College of Physicians 7
• Switching from daily oral therapy to Cabenuva offers potential metabolic benefits, including reduction in NRTI-related bone, kidney, and cardiovascular complications, as noted by the European AIDS Clinical Society 8, 9

Quality of Life and Morbidity Considerations

• This regimen prioritizes quality of life through maintaining durable virological suppression, with 95% suppression rates in clinical trials, as reported by the World Health Organization 7, 8
• Injection site reactions are common but rarely lead to discontinuation, with only 1-6% discontinuing due to adverse events, according to the National Institutes of Health 7, 8

Bridging Antiretroviral Therapy with Biktarvy

Introduction to Bridging Therapy

• The American Medical Association recommends bridging a patient with Biktarvy during a planned missed Cabenuva injection, as it represents a highly effective strategy given Biktarvy's high barrier to resistance and proven efficacy even in patients with archived NRTI resistance 10, 11

Clinical Approach to Bridging

• Start Biktarvy at the time the next Cabenuva injection would have been due, either at the 4-week or 8-week mark, depending on the patient's dosing schedule, to minimize risk of subtherapeutic drug levels and potential resistance development 11, 12
• Continue Biktarvy for the entire duration of the missed injection period plus at least 1-2 weeks beyond when the patient returns for their next scheduled Cabenuva injection to ensure adequate drug levels are maintained during the transition back to long-acting therapy 10

Rationale for Biktarvy as a Bridge Option

• Bictegravir combined with two NRTIs maintains efficacy even in patients with archived M184V/I mutations, making it robust for bridging scenarios where resistance concerns may exist 10, 11
• The integrase inhibitor bictegravir has a high genetic barrier to resistance development, which minimizes the risk of resistance during the bridge period 10, 11

Monitoring During the Bridge Period

• Emphasize the critical importance of daily Biktarvy adherence during the bridge period, as missed oral doses create greater risk for resistance than the long-acting formulation 11, 12
• Check HIV RNA at 4-6 weeks after resuming Cabenuva injections to ensure successful transition back to long-acting therapy 10

Special Considerations

• If the bridge period extends beyond 2-3 months or if there are adherence concerns, consider resistance testing before resuming Cabenuva to ensure no emergent resistance to rilpivirine or integrase inhibitors has developed 10
• Cabenuva carries a 1-2% risk of virologic failure with emergence of both integrase inhibitor and NNRTI resistance even with perfect adherence, a risk not seen with oral regimens like Biktarvy 10, 11, 12