Action of Proton pump inhibitors are most effective when they are given:

Proton pump inhibitors should be taken 15-30 minutes before meals. This allows absorption of the medication to provide availability to the proton pumps when they are activated by the meal. This drug when taken before meals provide the best intragastric pH control. PPIs are inactive at neutral pH. At pH < 5 the drug rearranges into two charged cationic forms (a sulfenic acid and a sulphenamide configuration). They react covalently with SH group of the H+ K+ ATPase enzyme and inactivate it irreversibly. Acid secretion resumes when new H+ K+ ATPase molecules are synthesized. Ref: Advanced Therapy in Gastroenterology and Liver Disease By Theodore M. Bayless, 5th Edition, Page 56 ; Essentials of Medical Pharmacology By K D Tripathi, 5th Edition, Page 593