A 52-year-old man with a 10-year history of GERD presents to the outpatient clinic. He has been on omeprazole 20 mg daily for the past 8 years with good symptom control. Which is the most common adverse effect associated with long-term PPI use that he is at risk of developing?

Explanation

## Most Common Adverse Effect of Long-Term PPI Use **Key Point:** Hypomagnesaemia is the most frequent clinically significant adverse effect of chronic PPI therapy, occurring in 13–61% of long-term users. ### Mechanism of Hypomagnesaemia PPIs inhibit magnesium absorption in the small intestine through: 1. Reduced gastric acid → decreased solubility of dietary Mg²⁺ 2. Impaired active transport via TRPM6 channels (acid-dependent) 3. Cumulative effect over months to years of therapy ### Clinical Consequences | Manifestation | Details | |---|---| | Asymptomatic hypomagnesaemia | Most common presentation; detected on routine labs | | Symptomatic hypomagnesaemia | Muscle weakness, tremor, personality changes, cardiac arrhythmias | | Secondary hypocalcaemia | Mg²⁺ required for PTH secretion and action | | Hypokalemia | Refractory to K⁺ supplementation if Mg²⁺ not corrected | **Clinical Pearl:** Always check serum magnesium in patients on PPIs >1 year, especially if they develop unexplained hypokalemia or cardiac arrhythmias. Mg²⁺ supplementation (200–400 mg/day) is often required. ### Why Other Options Are Less Common - **Acute interstitial nephritis:** Rare, reported but not the most common - **C. difficile infection:** Risk is increased but occurs in <5% of PPI users; hypomagnesaemia is far more frequent - **Hepatic cirrhosis:** No causal link; not a recognized PPI adverse effect **High-Yield:** Hypomagnesaemia is so common with long-term PPIs that baseline and periodic monitoring is recommended by major gastroenterology societies. [cite:KD Tripathi 8e Ch 50]