Biotin-Induced Proximal Renal Tubular Acidosis in an Adolescent Female: Report of a Rare Case With Rechallenge Confirmation

Proximal renal tubular acidosis (RTA) results from impaired bicarbonate reabsorption in the proximal renal tubule, leading to a normal anion gap metabolic acidosis and electrolyte abnormalities. We report the case of a 16-year-old previously healthy female who presented with recurrent episodes of hypotension, dizziness, and generalized weakness over one month. Laboratory evaluation demonstrated severe hypokalemia, hyperchloremic metabolic acidosis with a normal anion gap, and glucosuria in the absence of hyperglycemia, with preserved renal function. Extensive evaluation for endocrine and autoimmune causes was unrevealing. A detailed review of medications and supplements identified recent initiation of high-dose biotin supplementation (2,500 µg daily) for cosmetic purposes. A strong temporal association was noted between biotin exposure and symptom onset, with rapid clinical and biochemical improvement following discontinuation. Two months later, inadvertent re-exposure to biotin resulted in recurrence of symptoms and laboratory abnormalities, which again resolved promptly after cessation of the supplement. The patient was managed with intravenous fluids, potassium supplementation, and avoidance of biotin, leading to sustained resolution of symptoms. At one-month follow-up, she remained asymptomatic with normal electrolyte levels and preserved renal function. This case identifies biotin as a rare, reversible cause of proximal RTA and underscores the importance of obtaining a thorough supplement history when evaluating patients with otherwise unexplained metabolic acidosis.