MO116: Vitamin C Nephrotoxicity in a COVID-19 Patient: A Case Report
Authors: Lemee Noémie , Chamley Paul , Francois Alexis , Guincestre Thomas , Duval Marion , Promerat Aude , Lemoine Cécile 
Published: May 2022

Abstract

BACKGROUND AND AIMS
During the time of the COVID-19 pandemic, multiple treatment options have been investigated, even though their efficacy and secondary effects remain insufficiently known.
We report the case of a vitamin C induced oxalate nephropathy in a COVID-19 patient with preexisting chronic kidney disease (CKD) resulting in irreversible acute renal failure.
Vitamin C, also known as ascorbic acid, has been used as an anti-inflammatory therapy for COVID-19, but review of the literature shows similar cases of acute kidney injury (AKI), raising concern.

METHOD
We report the case of a 73-year-old Caucasian woman admitted for hyperthermia and digestive disorders. She had recently started a first-line chemotherapy for multiple myeloma with partial response. She also displayed preexisting stage 4 CKD (eGFR 18.50 mL/min/1.73 m² using CKD-EPI) of unknown aetiology.
She was tested positive for SARS-CoV2 by nasopharyngeal swab and soon transferred to the intensive care unit. She received intravenous corticosteroids using dexamethasone 6 g/24 h for 10 days and a piperacillin + tazobactam probabilistic antibiotherapy. She also received high doses (15 g/24 h) of vitamin C for three consecutive days. No monoclonal antibodies were prescribed due to a previous vaccination with a positive serology upon admission.
Although the patient recovered from respiratory tract infection, her kidney function progressively deteriorated with serum creatinine levels rising up to 8.06 g/dL, leading to her admission in our nephrology department. The patient was initially treated with high doses of diuretics for anasarca and an abdominal CT excluded urinary tract obstruction with normal kidney size and aspect. Urinary analysis showed protein to creatinine (p/c) ratio of 1348 g/g, and presence of urinary light chains. Her monoclonal spike was measured at 2.3 g/L and her kappa/lambda fraction was 1.74.
Intermittent haemodialysis was initiated, and a kidney biopsy was performed.

RESULTS
Histology revealed hundreds of intratubular calcium oxalate crystals, with severe and diffuse acute tubular necrosis and interstitial edema. There was no amyloidosis, no sign of active glomerular disease and no interstitial fibrosis. Immunofluorescence (IgA, IgG, IgM, C1Q, C3, kappa and lambda) was negative. We concluded to oxalate nephropathy.
After a 2-month follow-up, the patient remains dialysis dependent.
Vitamin C is a precursor of oxalate and has been shown to cause secondary oxaluria, particularly with high-dose regimens in patients with altered renal function. Given the histological findings evocative of acute oxalate nephropathy, the accountability of high doses of vitamin C should be considered.
No other cause of hyperoxaluria was identified in our patient beside broad spectrum antibiotic use, which could decrease intestinal bacterial oxalate degradation. In particular, there was no malabsorption
The limitation of our report is the unknown cause of preexisting CKD; therefore, we cannot rule out preexisting hyperoxaluria. Also, no dosage of serum vitamin C and oxalate levels were performed during follow-up. Finally, our patient had other possible causes AKI, such as recent SARS-CoV2 infection, or linked to multiple myeloma, but these were considered unlikely given the proper haematological response to treatment and non-evocative biopsy.
The rationale for vitamin C use in COVID-19 is based on in vitro studies showing its antioxidant, anti-inflammatory, anticoagulant and immune modulatory properties. There lack large clinical studies, and the literature shows conflicting results. Multiple cases of acute oxalate nephropathy were described.

CONCLUSION
Vitamin C is an anti-inflammatory treatment used in COVID-19 that can lead to secondary hyperoxaluria with significant and irreversible AKI. Due to the severity of AKI in patients with preexisting CKD, we believe renal function should be considered before using high doses of vitamin C.
Larger controlled trials are needed both to establish the clinical benefit of vitamin C and further describe its potential nephrotoxicity.