Derek L Capsule SR is a combination of two medicines: Levosulpiride and Rabeprazole which relieve symptoms of gastroesophageal reflux disease (GERD) and intestinal ulcers. Levosulpiride is a prokinetic which works by increasing the release of acetylcholine (a chemical messenger). This increases the movement of stomach and intestines, and prevents reflux (acid going up to the food pipe). Rabeprazole is a proton pump inhibitor (PPI). It works by reducing the amount of acid in the stomach which helps in the relief of acid-related indigestion and ulcers.