Severe hypophosphatemia induced by denosumab in a patient with osteomalacia and tenofovir disoproxil fumarate-related acquired Fanconi syndrome

Acquired disorders of phosphaturia: Beyond tumor-induced osteomalacia

Phosphate is an integral part of human cellular structure and function. Though most recognised disorders of phosphaturia are genetic in origin, phosphate loss due to acquired conditions is commonly encountered in clinical practice. Acquired hypophosphatemia is most commonly due to renal phosphate wasting and can produce significant morbidity. It also heralds future kidney damage, and continued exposure can lead to progressive kidney injury and potentially renal failure. These conditions are a diverse group of disorders with common shared mechanisms causing loss of phosphate in the urine. Renal phosphate loss can occur as an isolated entity or as a part of generalised proximal tubular dysfunction, i.e., Fanconi's syndrome. An insight into the pathophysiological mechanisms of acquired phosphaturia can help clinicians monitor their patients better and avoid potential harms.

Fanconi syndrome induced by the long-term use of tenofovir disoproxil fumarate: a case report and literature review

We present the case of a woman of 50 years of age who experienced widespread bone pain along with digestive symptoms, including nausea and vomiting. She had been prescribed tenofovir disoproxil fumarate (TDF) tablets for the treatment of hepatitis B. Laboratory testing revealed low circulating phosphorus and potassium concentrations and acidosis. A whole-body bone scan revealed abnormal bone metabolism. Rheumatologic and urologic conditions were ruled out, and therefore TDF-induced Fanconi syndrome (FS) and related bone pain was diagnosed. After the TDF was discontinued, the patient's symptoms and laboratory indices significantly improved. In this manuscript, we highlight the clinical manifestations of and laboratory test results associated with FS and summarize the cases of TDF-induced FS reported on PubMed between 2013 and 2022 to improve understanding of FS.

Diagnosis and Management of Denosumab-Induced Hypocalcemia and Hypophosphatemia in the Setting of Metastatic Prostate Cancer

Denosumab, a receptor activator of nuclear factor kappa-Β ligand (RANK-L) monoclonal antibody used in osteoporosis and various malignancies, has been shown to cause hypocalcemia shortly after initiation of treatment. There have been few case reports of electrolyte abnormalities in patients managed with long-term treatment with this medication. This report presents the case of a 43-year-old male with metastatic prostate cancer who presented with severe hypophosphatemia and hypocalcemia, initially resistant to repletion. After more aggressive and persistent repletion with IV calcium, phosphorus, and vitamin D, as well as time for the denosumab to dissipate, the patient’s electrolytes stabilized and he was able to be discharged with oral replacement and close follow-up. Therefore, long-term monitoring of electrolytes for patients on denosumab should be carefully considered.

Pharmacokinetics of Tenofovir Alafenamide Fumarate and Tenofovir in the Chinese People: Effects of Non-Genetic Factors and Genetic Variations

Background

Tenofovir alafenamide fumarate (TAF) was approved for HBV treatment in China in 2018. Despite higher antiviral efficacy and less impact on renal function and bone mineral density, the pharmacokinetic profiles of TAF are highly variable. The objectives of this study were to investigate the pharmacokinetics of TAF in the Chinese population and explore the associations between TAF and genetic polymorphisms and non-genetic factors.

Patients and Methods

A total of 64 healthy Chinese subjects aged 18~65 years old were planned to enroll. According to the dietary intake status, the subjects were divided into two groups (n = 32 per group). The concentrations of TAF and tenofovir were measured by HPLC-MS/MS, and the single-nucleotide polymorphisms were analyzed by MALDI-TOF MS.

Results

All the enrolled participants (18–35 years) completed the clinical trial study. Similar to the results reported in other ethnic populations, the pharmacokinetic profiles of TAF and tenofovir were highly variable in the Chinese people, and the HFHC diet can significantly increase the systemic exposure of TAF. We determined both HFHC diet and rs7311358 (SLCO1B3) genotypes were independently associated with TAF AUC_0-t, while HFHC diet, age and rs3740066 (ABCC2) variants were predictive of t_1/2 of tenofovir (P < 0.05). The subjects with the AA genotype in rs7311358 had significantly higher TAF AUC_0-t values (1.15 times) than those with a G allele, and the t_1/2 of tenofovir in the rs3740066 TT genotype group was 1.23 times longer than that of CC genotype group. Furthermore, there was a trend of higher TAF AUC and shorter tenofovir t_1/2 for the rs2032582 (ABCB1) T allele and rs3742106 (ABCC4) CC variant, respectively, although not statistically significant in the multiple linear regression analysis.

Conclusion

This study provided new evidence to suggest a critical link between both genetic and non-genetic factors and TAF pharmacokinetics in the Chinese people.

Fanconi Syndrome Induced by Tenofovir in a Diabetic Patient with a History of Chronic Hepatitis B: A Case Report

Tenofovir disoproxil fumarate is a nucleotide reverse transcriptase inhibitor and has been extensively used in the first-line treatment of viral infectious diseases such as chronic hepatitis B. Despite its good safety, the development of Fanconi syndrome is a rare adverse effect of long-term tenofovir therapy. Here, we report a case of a 62-year-old diabetic woman with a history of chronic hepatitis B who was exposed to tenofovir and developed drug-associated Fanconi syndrome. After discounting tenofovir, the patient's bone pain was markedly reduced.

Impact of Tenofovir Disoproxil-Induced Fanconi Syndrome on Bone Material Quality: A Case Report

Tenofovir is a nucleotide analog reverse‐transcriptase inhibitor (NtARTI) used for treatment of chronic hepatitis B and human immunodeficiency virus (HIV). Fanconi syndrome (FS) is a condition affecting the proximal tubules of the kidney, leading to increased passage and impaired reabsorption of various small molecules such as glucose, phosphate, bicarbonate, and amino acids. Tenofovir disoproxil fumarate (TDF) is one of two pro‐drugs of tenofovir associated with a greater nephrotoxicity and renal complications such as FS with subsequent osteomalacia, acute kidney injury, and reduction of glomerular filtration rate (GFR) compared with tenofovir alafenamide (TAF). We present the case of a 33‐year‐old white woman treated with TDF because of chronic hepatitis B infection suffering four atraumatic fractures over the period of 2 years. The patient was taken off the TDF regimen 3 months before presentation. Initial blood and urine samples suggested the presence of TDF‐induced osteomalacia, which was confirmed by transiliac bone biopsy and histomorphometry. Moreover, bone mineral density distribution (BMDD) by quantitative backscattered electron imaging (qBEI) analysis showed that approximately 56% of the bone surface was normally mineralized and 44% showed a reduced mineralization consistent with the presence of osteomalacia. The patient made a significant recovery upon cessation of the causative agent. This case report emphasizes the use of bone biopsy, histomorphometry and qBEI in confirming the diagnosis of drug‐induced Fanconi syndrome and associated osteomalacia. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Denosumab improves clinical manifestations of hypophosphatemic osteomalacia by adefovir-induced Fanconi syndrome: a case report

Background

Adefovir dipivoxil is a nucleotide analogue that is approved for treatment of chronic hepatitis B. Adefovir dipivoxil is associated with proximal tubular dysfunction, resulting in Fanconi syndrome, which can cause secondary hypophosphatemic osteomalacia. We describe a case of a patient with hypophosphatemic osteomalacia secondary to Fanconi syndrome induced by adefovir dipivoxil concomitantly with osteoporosis in whom clinical symptoms were improved by adding denosumab (a human monoclonal antibody targeting the receptor activator of nuclear factor-κB ligand) to preceding administration of vitamin D₃.

Case presentation

A 60-year-old Japanese man had been receiving low-dose adefovir dipivoxil (10 mg/day) to treat chronic hepatitis B for approximately 5 years. He presented to an orthopedic surgeon with severe pain of the right hip and no trauma history, and fracture of the neck of the right femur was identified. In addition, ^99mTc-hydroxymethylene diphosphate scintigraphy revealed significantly abnormal uptake in the bilateral ribs, hips, and knees, and he was therefore referred to our university hospital for evaluation of multiple pathological fractures. We diagnosed hypophosphatemic osteomalacia due to Fanconi syndrome induced by adefovir dipivoxil therapy. Although we reduced the patient’s adefovir dipivoxil dose and added calcitriol (active vitamin D₃), he did not respond and continued to complain of bone pain. Several bone resorption markers and bone-specific alkaline phosphatase were also persistently elevated. Therefore, we added denosumab to vitamin D₃ supplementation for treatment of excessive bone resorption. Two months after initiation of denosumab, his hip and knee pain was relieved, along with a decrease in serum alkaline phosphatase and some bone resorption markers.

Conclusions

Although denosumab is not generally an appropriate treatment for acquired Fanconi syndrome, it may be useful for patients who have hypophosphatemic osteomalacia due to adefovir dipivoxil-induced Fanconi syndrome associated with excessive bone resorption. However, clinicians should keep in mind that if denosumab is administered to patients with hypophosphatemic osteomalacia accompanied by excessive bone resorption, adequate vitamin D and/or phosphate supplementation should be done before administration of denosumab.