QUESTION: Can I give IV vitamin C to a patient who has a significant history of kidney stones? How much do I have to worry about oxalate stones?
ANSWER: This question has followed IVC for ‘ever’, and as two of the high grade adverse events were oxalosis, it requires a somewhat formed thought and reply.
Some things to consider: IV ASC does increase oxalate in the urine when checked post IV, but not for long (unpublished observational data from long ago by myself). Of note, none of the patients checked with transient elevated oxalate in the urine ever had a stone. In an analysis of over 85,000 women who had no history of Ki stones, use of ASC orally was not associated with stone formation, but B-6 showed some promise for decreasing stone formation. [JASN April 1, 1999 vol. 10 no. 4 840-845]. “Conclusions: Our results suggest that ≥40 mg/d of vitamin B6 intake may reduce the risk of stone formation in women. However, our findings for vitamin C, which have been consistent for women and men, do not support the practice of routine restriction of vitamin C to prevent kidney stones.” In hemolysis however, (rarely our population) B-6 does not appear to be protective [J Am Soc Nephrol. 1992 Oct;3(4):1018-24. etc etc] Put this, and other things, together and you see what in two decades doing this, as well as that study I quoted and most every other clinician has seen, no real issue with oxalate stone formation in people with kidney function at 40 or above eGFR.
Also, in “stone formers” we do watch the eGFR carefully and monitor them for Sn/Sx as we go, and imaging of the kidneys before treatment is needed. But I have one in Tx right now and we’ve not had a stone trigger in a year. Some add B-6 to the IVC and that may be helpful if not a dialysis patient, but PO dosing would be more likely “better” if doing that as a preventive strategy. The theory with the eGFR cut off and monitoring and those two cases of renal oxalosis is that the normal oxalate dump is fine in decent Ki function, but in low Ki function it can’t clear the oxalates fast enough, so they crystallize.