Objective: To examine retrospectively the effect of proton pump inhibitors (PPIs) on thyrotropin (thyroid-stimulating hormone or TSH) values in patients with hypothyroidism and normal TSH levels receiving levothyroxine (LT4) replacement therapy.
Methods: The data collection was done by retrospective review of electronic medical records from the period of December 2002 to August 2005 from patients with hypothyroidism who were receiving at least 25 mug of LT4 replacement daily at Queens Hospital Center. The first 92 patients meeting all inclusion and exclusion criteria were included in the study. The study group (N = 37) patient data were collected by selecting euthyroid patients who had received stable LT4 replacement for at least 6 months and in whom PPI therapy (lansoprazole) was later initiated. TSH levels were collected before and at least 2 months after the PPI treatment was started. The control group (N = 55) patient data were collected by reviewing TSH levels among euthyroid patients with a history of hypothyroidism receiving stable LT4 therapy and not receiving a PPI during the period of data collection. The statistical analysis was done by comparing the mean change in TSH level in each group with use of the Student t test.
Results: In the study group, the mean change in the TSH level from before to at least 2 months after initiation of PPI therapy, 0.69 +/- 1.9 micro IU/mL, was statistically significant (P = 0.035). In the control group, the mean change in the TSH level during the study period, 0.11 +/- 1.06 micro IU/mL, was not statistically significant (P = 0.45).
Conclusion: To our best knowledge, this is the first study in humans with hypothyroidism demonstrating the effect of PPIs on serum TSH levels. PPIs should be added to the list of medications affecting the level of thyroid hormone in patients with hypothyroidism treated with LT4 replacement. Patients with hypothyroidism and normal TSH values during LT4 replacement therapy may need additional thyroid function testing after treatment with PPIs and may need adjustment of their LT4 dose.