Rifampin monotherapy for children with idiopathic infantile hypercalcemia.

Area of Science:

• Pediatric Endocrinology
• Genetics and Molecular Biology
• Pharmacology

Background:

• Idiopathic Infantile Hypercalcemia (IIH) involves elevated 1,25(OH)2D, leading to hypercalcemia and hypercalciuria.
• Existing treatments for IIH, including dietary restrictions, offer limited success.
• Rifampin induces CYP3A4, potentially aiding 1,25(OH)2D inactivation, showing promise for HCINF1.

Purpose of the Study:

• To evaluate rifampin's efficacy in reducing serum 1,25(OH)2D, calcium, and urinary calcium in HCINF3 patients.
• To compare rifampin's effectiveness in HCINF3 with a control subject having HCINF1.
• To assess the safety and tolerability of rifampin in treating IIH subtypes.

Main Methods:

• A study involving four HCINF3 subjects and one HCINF1 control, treated with rifampin (5 and 10 mg/kg/day) for two months each, with a two-month washout period.
• Patients maintained age-appropriate dietary calcium intake and 200 IU vitamin D daily.
• Primary outcome: reduction in serum 1,25(OH)2D. Secondary outcomes: changes in serum calcium, urinary calcium:creatinine ratio, and 1,25(OH)2D/PTH ratio.

Main Results:

• Rifampin was well-tolerated and induced CYP3A4 in all participants.
• The HCINF1 control showed significant decreases in serum 1,25(OH)2D and the 1,25(OH)2D/PTH ratio.
• HCINF3 patients exhibited reduced 1,25(OH)2D and urinary calcium:creatinine ratio at 10 mg/kg/day, but hypercalcemia persisted with variable 1,25(OH)2D/PTH responses.

Conclusions:

• Rifampin demonstrates potential for managing hypercalcemia in specific IIH subtypes, particularly HCINF1.
• While rifampin reduced 1,25(OH)2D and urinary calcium in HCINF3, it did not fully resolve hypercalcemia.
• Further long-term studies are warranted to establish rifampin's therapeutic role in Idiopathic Infantile Hypercalcemia.