How Does GERD Affect Levothyroxine Absorption?

Levothyroxine is the most-prescribed generic drug in the world.

This common treatment for hypothyroidism is dosed at 2 mcg/kg to 3 mcg/kg of lean body weight. However, its absorption is highly variable, as levothyroxine levels can be altered by gastrointestinal reflux disease (GERD) and its treatments, in addition to fasting, inflammatory bowel disease, lactose intolerance, gastroparesis, gastric bypass surgery, mineral supplements, and other medications.

Past studies have shown that up to 48% of patients have thyroid-stimulating hormone levels outside the therapeutic range. Clinicians can identify factors that affect control via patient-prescriber dialogue, but often, the pressures of time make it impossible to do so.

Now, an article published ahead-of-print in the journal Drugs in R&D indicates that prescribers can prospectively identify gastrointestinal comorbidities and allergies affecting levothyroxine absorption.

The CONTROL Surveillance Project enrolled English-speaking patients in the United States receiving medication for hypothyroidism. The 925 participants completed a 21-item online survey on the Research Now platform. Around 8% of these patients had more than 5 levothyroxine dose changes in the previous year.

One-third of participants had GERD, and around 41% reported taking antacids, histamine receptor antagonists, or proton pump inhibitors. Both GERD and its common treatments are recognized for impairing levothyroxine absorption.

Patients with comorbid gastrointestinal disorders said they found it hard to control their thyroid levels, with more of these individuals reporting multiple dose changes in the past year. Patients with comorbidities were almost twice as likely to have multiple dose changes as patients who had no comorbidities, indicating concurrent disease or medication are risk factors for altered levothyroxine absorption. Patients with comorbidities also reported lower satisfaction with their therapy.

About 1 in 10 patients had irritable bowel syndrome and food allergies, and inflammatory conditions like these can impair levothyroxine absorption.

Prescriber review of comorbidities and other medications can improve hypothyroidism control. One factor that should trigger a discussion with the patient is higher-than-recommended levothyroxine levels.

Improved control lowers medical spending by avoiding frequent physician and pharmacy visits, medication adjustments, and laboratory tests, as well as poor compliance.

The overrepresentation of Caucasians (typical of online surveys) and lack of access to patient medical records (eg, thyroid levels) limited this study’s external validity.