Drug General Information (ID: DDIEVWXL7P)
Drug Name			Levothyroxine		Drug Info		Rabeprazole		Drug Info
Drug Type		Small molecule				Small molecule
Therapeutic Class		Antithyroid Agents				Antiulcer Agents
Structure

Mechanism of Levothyroxine-Rabeprazole Interaction (Severity Level: Moderate)
Altered gastric pH Click to Show/Hide Mechanism Graph
Drug Name		Levothyroxine				Rabeprazole
Mechanism		Gastric pH sensitive				Gastric alkalinizer
Key Mechanism Factor 1
		Factor Name		Gastric pH
		Factor Description		The normal pH range of gastric acid is between 1.5 and 3.5 and is highly acidic, consisting mainly of hydrochloric acid. Changes in the pH of the stomach can alter the absorption of drugs.
Mechanism Description		Decreased absorption of Levothyroxine due to altered gastric pH caused by Rabeprazole

Recommended Action
Management		Caution is advised if levothyroxine is used concomitantly with proton pump inhibitors. Consider the alteration in gastric pH caused by the PPI. Some authorities recommend separating administration of PPI and levothyroxine by several hours, however there are no studies showing improved absorption when PPIs are administered separately from levothyroxine. If concomitant administration is necessary, consider monitoring TSH level and watching for clinical evidence of reduced levothyroxine effects. Patients should be advised to contact their physician if they experience symptoms of hypothyroidism, such as fatigue, cold intolerance, constipation, unexplained weight gain, depression, joint or muscle pain, thinning hair or hair loss, dry skin, hoarseness, and abnormal menstrual periods.

References
1	Cerner Multum, Inc. "Australian Product Information.".
2	Cerner Multum, Inc. "UK Summary of Product Characteristics.".
3	Product Information. Synthroid (levothyroxine). Abbott Pharmaceutical, Abbott Park, IL.