NutriStack
What is happening. Ganciclovir, the active form of valganciclovir, is renally cleared and can be nephrotoxic, with kidney impairment requiring dose reduction. Chronic high-dose vitamin C (gram-level doses) increases urinary oxalate and has been associated with calcium-oxalate kidney stones and, rarely, oxalate nephropathy. Combining habitual high-dose vitamin C with a renally cleared, potentially nephrotoxic antiviral adds an unnecessary kidney stressor in patients whose renal function directly governs safe drug dosing.
Mechanism. Ascorbic acid is metabolized to oxalate; high intake raises urinary oxalate and the risk of calcium-oxalate crystal deposition. This adds to ganciclovir's potential for renal tubular injury, and because ganciclovir clearance depends on kidney function, any reduction in renal function can raise drug exposure and toxicity.
Recommendation. Avoid sustained high-dose vitamin C (more than about 1,000 mg/day) during valganciclovir therapy, especially in anyone with reduced kidney function, dehydration, or a history of kidney stones. Maintain good hydration and stay near the recommended daily intake from food and modest supplementation.