Endocrine Abstracts

Background: Proximal tubule dysfunction in Fanconi syndrome causes impaired reabsorbtion of amino acids, glucose, urate and phosphate, which leads to hypophosphatemic osteomalcia. Adefovir and tenofovir are two nucleoside reverse transcriptase inhibitors, which are used for treatment of patients with hepatitis B infection. Although these drugs are well tolerated with few side effects, patients may rarely suffer from drug-induced Fanconi syndrome and hypophosphatemic osteomalacia.

Clinical case: Patient-1, a-63-year-old male patient, referred to Endocrinology and Metabolism Clinic suffering from right knee pain for 3 months which became bilateral in course of time. He also had pain in lomber region, in legs and feet. He has been on adefovir treatment for hepatitis B infection for 10 years. His phosphorus (P) level was 1.1 mg/dl, calcium (Ca) level was 9.05 mg/dl and ALP level was 153 mg/dl. His tubular maximum of phosphate corrected for GFR was low for his GFR, age and gender. His FGF23 level was suppressed. After treatment with calcitriol 50 μg and with 1500 mg/day phosphorus, his phosphate levels reached to normal levels with amelioration of symptoms within 1 year and dose was tapered according to clinical and laboratory assessment. Patient-2-, a 64-year-old-male patient, applied to Endocrinology and Metabolism Clinic suffering from loss of balance, difficulty in walking, bilateral hip and knee pain and general muscle pain for 4 years. He had been walking with the help of crutch for 2 years. He was on treatment with tenofovir for 5 years for hepatitis B infection. His serum Ca was 8.78 mg/dl, P was 1.2 mg/dl and ALP level was 242 mg/dl. His tubular maximum of phosphate corrected for GFR was low for his GFR, age and gender. He is on treatment with calcitriol 0.25 μg and 1500 mg/day phosphorus with normalization of calcium and phosphorus levels as well as amelioration of symptoms. Due to previous lamivudine resistance, entacavir treatment was recommended after cessation of tenofovir for treatment of hepatitis B infection.

Conclusion: Drug induced Fanconi syndrome and hypophosphatemic osteomalacia should be kept in mind in patients receiving nucleoside analogue treatment for hepatitis B who suffer from bone pain and muscle weakness.