A 48-year-old woman with a 3-year history of GERD is on omeprazole 20 mg once daily with good symptom control. She now presents with new-onset fatigue, macrocytic anemia (Hb 8.2 g/dL, MCV 108 fL), and low serum B12 (180 pg/mL). Intrinsic factor antibodies are negative and parietal cell antibodies are negative. What is the most appropriate next step in management?

Explanation

## Clinical Context This patient has developed PPI-associated vitamin B12 deficiency. Long-term PPI use impairs intrinsic factor-independent absorption of food-bound B12 by suppressing gastric acid and reducing pepsin activity (needed to release B12 from food proteins). The negative autoimmune markers rule out pernicious anemia. ## Pathophysiology of PPI-Induced B12 Deficiency ```mermaid flowchart TD A[Long-term PPI use]:::action --> B[Reduced gastric acid & pepsin]:::outcome B --> C[Impaired food-bound B12 release]:::outcome C --> D[Decreased B12 absorption in terminal ileum]:::outcome D --> E[B12 depletion over 2-3 years]:::outcome E --> F[Macrocytic anemia + neurologic symptoms]:::urgent F --> G[Supplement B12 + continue PPI at current dose]:::action ``` ## Rationale for Correct Answer **Key Point:** PPI-induced B12 deficiency is a well-recognized adverse effect occurring in 10–30% of patients on long-term PPI therapy (>2 years). The mechanism is impaired absorption of food-bound B12 due to achlorhydria, NOT intrinsic factor deficiency (hence negative autoimmune markers). **High-Yield:** The most appropriate next step is **Option A — start vitamin B12 supplementation and continue omeprazole at the current dose**. The patient has good GERD symptom control on omeprazole 20 mg once daily; there is no indication to reduce the dose, switch agents, or discontinue therapy. B12 supplementation (oral high-dose cyanocobalamin 1000 mcg/day or parenteral) effectively corrects the deficiency regardless of the underlying mechanism, because high-dose oral B12 is absorbed by passive diffusion independent of intrinsic factor and gastric acid. **Why not Option D (continue + supplement + reassess in 3 months)?** Option D is subtly inferior because it implies a passive "wait and see" approach without specifying that supplementation should begin immediately. In a symptomatic patient with Hb 8.2 g/dL and confirmed B12 deficiency, supplementation must be initiated promptly — not deferred pending a 3-month reassessment. Option A correctly captures the immediate action required. **Clinical Pearl:** Discontinuing the PPI (Option C) is NOT the first step because: 1. The patient has good GERD control on current therapy 2. Rebound acid hypersecretion may occur on abrupt discontinuation 3. B12 supplementation is safe, effective, and corrects the deficiency without altering GERD management 4. Dose reduction (Option B) lacks guideline support as a strategy for managing PPI-induced B12 deficiency ## PPI-Associated Nutrient Deficiencies | Nutrient | Mechanism | Incidence | Management | |---|---|---|---| | Vitamin B12 | Impaired food-bound B12 release | 10–30% | Supplementation; continue PPI | | Iron | Reduced gastric acid | 5–10% | Iron supplementation; consider dose reduction | | Calcium | Reduced acid-dependent absorption | 5–15% | Calcium citrate (not carbonate); monitor BMD | | Magnesium | Reduced absorption | 13–25% | Magnesium supplementation | **Mnemonic:** **BFIM** — B12, Iron, Magnesium, Calcium are the main nutrients affected by long-term PPI use. [cite:Harrison 21e Ch 307; KD Tripathi 8e Ch 50]