Cyanocobalamin × Omeprazole

Proton pump inhibitors suppress gastric acidity and reduce B12 release from food (which requires HCl and pepsin). For short courses (up to 8 weeks), clinically insignificant. With long-term therapy (over 2 years), B12 deficiency risk is reported.

On long-term therapy: fatigue, pallor, paraesthesias in hands and feet, gait instability, memory decline.

For short omeprazole courses, no adjustment needed. On long-term therapy (over 2 years), check B12 yearly. If it falls below 200 pg/mL, give cyanocobalamin 500–1000 mcg/day orally — passive diffusion absorption at high doses works regardless of acidity.