What patient characteristic best supports using tenofovir alafenamide (TAF) over tenofovir disoproxil fumarate (TDF) in antiretroviral therapy (ART)?

Renal Insufficiency is the Best Characteristic Supporting TAF Over TDF in MT's Case

MT's renal insufficiency (creatinine clearance 45 mL/min) is the most compelling reason to authorize the non-preferred formulation containing tenofovir alafenamide (TAF) instead of tenofovir disoproxil fumarate (TDF).

Rationale for TAF in Renal Impairment

TAF is strongly preferred over TDF in patients with renal dysfunction for several important reasons:

1. Reduced Nephrotoxicity: TAF produces 90% lower plasma tenofovir concentrations compared to TDF, significantly reducing kidney-related adverse effects 1.

2. Safety in Renal Impairment: Guidelines specifically recommend TAF over TDF in patients with creatinine clearance <60 mL/min 1. MT's creatinine clearance of 45 mL/min falls well below this threshold.

3. Evidence of Benefit: Patients who switch from TDF to TAF experience improvements in renal function parameters:

   • Patients with eGFR <60 mL/min/1.73m² show improvements of 6.2 mL/min/1.73m² after switching to TAF 2
   • Significant decreases in proteinuria occur after switching from TDF to TAF 2, 3

Clinical Considerations for Each Patient Characteristic

Renal Insufficiency

• TDF is not recommended for patients with eGFR below 60 mL/min 1
• TAF is specifically indicated for patients with renal impairment with creatinine clearance above 30 mL/min 1
• MT's creatinine clearance of 45 mL/min makes her an ideal candidate for TAF

Diabetes

• While diabetes increases risk for kidney disease, it alone is not a specific indication for TAF over TDF
• However, diabetes combined with existing renal insufficiency further strengthens the case for TAF

Childbearing Age

• While pregnancy considerations are important, this alone is not a primary indication for TAF over TDF
• Limited data exist on TAF safety during pregnancy 1

High Viral Load

• Both TAF and TDF have comparable efficacy in viral suppression 4
• Viral load of 180,000 copies/mL does not specifically favor one formulation over the other

Evidence from Guidelines

The International Antiviral Society-USA panel specifically states that "TDF is not recommended for patients with an eGFR below 60 mL/min. The options are abacavir (which does not require dose adjustment in this setting) or TAF (if creatinine clearance is above 30 mL/min)" 1.

Monitoring Recommendations if TAF is Approved

If TAF is authorized:

• Continue monitoring renal function with serum creatinine (eGFR) every 3-4 months during the first year
• After the first year, monitor every 6 months if stable
• Monitor for improvements in proteinuria, which would be expected with TAF

Conclusion

Among the four patient characteristics presented (diabetes, renal insufficiency, childbearing age, and high viral load), renal insufficiency is clearly the strongest and most evidence-based indication for using TAF instead of TDF in MT's antiretroviral regimen. Guidelines explicitly recommend avoiding TDF in patients with creatinine clearance <60 mL/min, and research demonstrates significant renal benefits when switching from TDF to TAF in such patients.