Clinical management of hypophosphatemic osteomalacia induced by adefovir and tenofovir: Insights from a case report

Rationale: Hypophosphatemic osteomalacia is a rare chronic metabolic bone disease characterized by low serum phosphate levels owing to genetic or acquired causes. This article presents a case report of the clinical management, challenges encountered, and prognosis of secondary hypophosphatemic osteomalacia induced by defovir and tenofovir. Patient concerns: A 55-year-old male patient had been experiencing persistent dull chest pain and fatigue for more than a year. The patient had chronic hepatitis B infection for over 10 years, with regular use of adefovir dipivoxil capsules for more than 10 years. Five months before admission, the patient was switched to tenofovir alafenamide fumarate tablets. Diagnoses: After obtaining clinical manifestations, medical history, and examination results, tumor-induced osteomalacia was excluded, and the final diagnosis was drug-induced hypophosphatemic osteomalacia. Interventions: Adefovir dipivoxil and tenofovir alafenamide were discontinued, and the patient was switched to entecavir disintegration tablets for antiviral therapy. He was advised to follow a high-phosphate diet, receive phosphorus supplementation and calcitriol capsules to promote calcium absorption, obtain moderate sun exposure, and take measures to prevent falls and fractures. Outcomes: Serum phosphate levels showed a gradual upward trend, with the most recent measurement being 0.85 mmol/L. The bone density gradually improved and reached normal levels in the most recent assessment. The symptoms of fatigue and chest pain were resolved. Lessons: Accurate diagnosis requires a combination of clinical presentation, medical history, biochemical and radiological findings, and, if available, measurement of fibroblast growth factor 23 (FGF 23). The role of national, provincial, or regional centers for rare diseases is crucial for conducting unconventional tests and providing access to rare medications.