Hyponatremia in Patients Taking Biktarvy
Hyponatremia is not a recognized adverse effect of Biktarvy (bictegravir/emtricitabine/tenofovir alafenamide), and when it occurs in patients on this regimen, it should be evaluated as an independent clinical problem unrelated to the antiretroviral therapy.
Key Clinical Context
The FDA-approved prescribing information for Biktarvy does not list hyponatremia as an adverse reaction 1. In the pivotal clinical trials through 144 weeks, the most common adverse reactions (≥5%) were diarrhea, nausea, and headache—with no mention of electrolyte disturbances including hyponatremia 1. Large observational cohort studies of over 2,000 patients followed for 24 months similarly showed no signal for hyponatremia as a treatment-emergent adverse event 2.
Recognized Metabolic Effects of Biktarvy
The metabolic concerns with Biktarvy are distinctly different from hyponatremia:
Renal effects: Bictegravir causes small increases in serum creatinine through inhibition of tubular secretion (not actual GFR reduction) 3. Postmarketing cases of renal impairment, proximal renal tubulopathy, and Fanconi syndrome have been reported with TAF-containing products 1.
Lactic acidosis: Rare but serious cases of lactic acidosis have been documented, particularly in patients with renal impairment 1, 4. This is a nucleoside analog class effect from the emtricitabine and tenofovir components.
Evaluation Approach for Hyponatremia
When hyponatremia occurs in a patient on Biktarvy, pursue standard diagnostic evaluation:
Initial assessment:
- Volume status determination (hypovolemic, euvolemic, or hypervolemic)
- Serum osmolality, BUN, creatinine, uric acid, potassium
- Spot urine sodium and osmolality 5
Consider alternative causes:
- Opportunistic infections (particularly CNS infections in HIV patients)
- Medications other than Biktarvy (diuretics, SSRIs, carbamazepine, NSAIDs)
- SIADH from pulmonary or CNS pathology
- Adrenal insufficiency
- Hypothyroidism
- Volume depletion from diarrhea (which IS a common Biktarvy side effect)
Monitoring Recommendations
Current guidelines suggest basic metabolic panels are not routinely needed 4-8 weeks after starting first-line ART regimens like Biktarvy, and there is little evidence supporting every 6-month testing for regimens without TDF 3. However, monitoring should be performed when clinically indicated based on symptoms or comorbidities.
Specific monitoring for Biktarvy should focus on:
- Serum creatinine and estimated creatinine clearance at baseline and during treatment 1
- Urine glucose and protein in all patients
- Serum phosphorus in patients with chronic kidney disease 1
Management
Do not discontinue Biktarvy for hyponatremia alone. Treat the underlying cause of hyponatremia according to standard protocols based on volume status and severity. The only metabolic reason to discontinue Biktarvy would be development of lactic acidosis (lactate >4 mmol/L with metabolic acidosis) or clinically significant renal impairment with evidence of proximal tubulopathy 1, 4.
Critical Caveat
If a patient develops severe hyponatremia with altered mental status, consider atypical infections or immune reconstitution inflammatory syndrome (IRIS), which can occur in patients on effective ART 1. CNS opportunistic infections may present with SIADH and hyponatremia.