Should a 64-year-old male on Descovy (emtricitabine/tenofovir alafenamide) for pre‑exposure prophylaxis continue the medication despite a creatinine‑based eGFR of approximately 57 mL/min/1.73 m² and a cystatin C‑based eGFR of about 74 mL/min/1.73 m²?

Continue Descovy for PrEP in This Patient

You should continue Descovy (emtricitabine/tenofovir alafenamide) for this patient, as the cystatin C-based eGFR of 74 mL/min/1.73 m² more accurately reflects his true renal function and falls well within the safe range for TAF-based PrEP. The creatinine-based eGFR of 56-58 mL/min/1.73 m² is likely falsely low due to increased muscle mass or other factors that elevate creatinine without true kidney injury 1.

Why Cystatin C Matters Here

The discordance between creatinine-based eGFR (~57 mL/min) and cystatin C-based eGFR (74 mL/min) is clinically significant. Recent real-world data from PrEP clinics demonstrates that cystatin C testing frequently reveals that creatinine elevations overestimate renal dysfunction in PrEP users 1. In a cohort of 70 PrEP users with concerning creatinine values:

• When eGFR was calculated using creatinine alone, 15.7% had values <60 mL/min/1.73 m²
• When cystatin C was incorporated (CKD-EPI creatinine-cystatin formula), only 1.4% had eGFR <60 mL/min/1.73 m²
• Common confounders included protein supplements (61.4%), creatine use (41.4%), and high BMI (64.9%) 1

Your patient's stable creatinine values over multiple measurements (1.36-1.41) without progressive decline further supports that this represents his baseline rather than acute kidney injury.

Guideline Support for Descovy in This Scenario

The 2020 International Antiviral Society-USA guidelines specifically address this situation: Daily tenofovir alafenamide/emtricitabine is recommended for MSM with creatinine clearance between 30-60 mL/min who have osteopenia/osteoporosis or are at high risk for these complications 2. While your patient's cystatin C-based eGFR of 74 mL/min actually exceeds this threshold, the guideline establishes that TAF is the preferred formulation when there are renal concerns in the 30-60 mL/min range.

FDA Labeling Considerations

The Descovy FDA label states that Descovy is not recommended in individuals with estimated creatinine clearance of 15 to below 30 mL/min 3. Your patient's cystatin C-based eGFR of 74 mL/min is well above this threshold. The label also requires monitoring of renal function but does not mandate discontinuation at eGFR 50-60 mL/min when calculated by creatinine alone—particularly when alternative markers suggest better function.

The FDA label emphasizes: "Individuals taking tenofovir prodrugs who have impaired renal function and those taking nephrotoxic agents are at increased risk of developing renal-related adverse reactions" 3. However, it also states to "discontinue DESCOVY in individuals who develop clinically significant decreases in renal function" 3—your patient has stable, not declining, creatinine values.

Clinical Evidence Supporting Continuation

The DISCOVER trial demonstrated that emtricitabine/tenofovir alafenamide showed superior renal safety compared to TDF-based PrEP 4, 5. At 96 weeks, TAF maintained better renal biomarkers and bone mineral density than TDF while providing non-inferior HIV prevention efficacy 4.

Real-world data shows that complex kidney situations in PrEP users are rare (0.25 per 100 person-years) and often related to non-PrEP factors 6. In one cohort, 9 of 22 cases with eGFR <60 mL/min were linked to high-protein intake for weight training 6. Another study found that 84% of PrEP users with eGFR <60 mL/min required only conservative management (repeat sampling, stopping supplements/recreational drugs) rather than PrEP discontinuation 7.

Practical Management Algorithm

1. Continue Descovy based on cystatin C-based eGFR of 74 mL/min

2. Investigate and address reversible factors:

   • Assess for protein supplement use, creatine, anabolic steroids
   • Review for NSAIDs or other nephrotoxic medications
   • Check BMI and muscle mass (both elevate creatinine independent of kidney function)
   • Evaluate hydration status at time of lab draws

3. Monitor renal function every 3 months with:

   • Serum creatinine and eGFR
   • Urinalysis with protein-to-creatinine ratio
   • Consider repeat cystatin C in 6 months to confirm stability

4. Discontinuation criteria (none currently met):

   • Progressive decline in cystatin C-based eGFR
   • Development of proteinuria (>50 mg/mmol protein-to-creatinine ratio)
   • Clinical evidence of Fanconi syndrome (glucosuria, phosphaturia, proteinuria)

Common Pitfalls to Avoid

Do not reflexively discontinue PrEP based solely on creatinine-based eGFR in the 50-60 mL/min range. This leads to unnecessary PrEP discontinuation and potential HIV acquisition. The nephrology workup appropriately identified that creatinine was overestimating renal dysfunction 1.

Do not switch to TDF-based PrEP (Truvada), as TAF has superior renal safety profile, particularly in patients with any degree of renal concern 4, 5.

Do not ignore the stable trend. Three consecutive measurements showing creatinine 1.36-1.41 without progression suggests this is his baseline, not evolving kidney disease.

The evidence strongly supports continuing Descovy with appropriate monitoring in this patient whose true renal function by cystatin C is 74 mL/min/1.73 m² 2, 3, 1.