Endocrine Abstracts

Introduction: Patients with hypothyroidism are routinely advised to take levothyroxine without food or beverages but the pharmacokinetic effect of many common foods are unknown. We describe a patient with an unusually high levothyroxine requirement who only achieved adequate replacement by taking grapes along with levothyroxine. Through a cycle of challenge, withdrawal, and-re-challenge, we were able to demonstrate that levothyroxine availability was enhanced by grapes in this case.

Case report: A 30-year-old lady underwent total thyroidectomy for papillary thyroid cancer which had developed on a background of long-standing Hashimoto’s thyroiditis. Prior to this a stable euthyroid state had been maintained for many years with 100 μg daily of levothyroxine which she regularly took with grapes to make the tablets palatable. Following surgery she continued taking levothyroxine but was advised to avoid taking grapes with the tablets. Her thyroid status subsequently deteriorated and TSH remained persistently elevated even with levothyroxine doses as high as 350 μg daily. Other factors such as poor compliance, concomitant medication use, and co-morbid conditions like coeliac disease, malabsorption, and pernicious anaemia were excluded. Resumption of grapes led to a remarkable reduction of levothyroxine requirements to 125 μg daily. Three months afterwards she stopped taking grapes during a 3 weeks holiday abroad but continued to take levothyroxine on an empty stomach. Thyroid function a week after she returned showed that she had become hypothyroid again. Re-introduction of grapes with levothyroxine once more restored normal thyroid status.

Conclusion: To the best of our knowledge this is the first report of high levothyroxine requirements corrected by ingestion of grapes. The mechanism of this effect is unclear but it is plausible that the grapes provide a favourable acidic environment for levothyroxine absorption. Further studies will be required to confirm this effect and elucidate the underlying pharmacokinetic mechanisms.