CHANGES IN MANUFACTURER/BRAND
There are currently multiple brands and generic manufacturers supplying hypothyroid medications and reports that absorption rates and bioavailability vary among them.2 Switching products can result in changes in thyroid status and in TSH levels.
Once a patient has reached euthyroid status, it is imperative to stay on the same dose from the same manufacturer. This may be challenging, as it can be affected by the patient’s insurance carrier, policy changes, or even a change in the pharmacy’s medication supplier. Although patients are supposed to be informed by the pharmacy when the manufacturer is being changed, you may want to educate them to check the shape, color, and dose of their pills and also verify that the manufacturer listed on the bottle is consistent each time they refill their hypothyroid medications. This is especially important for those who require a very narrow TSH target, such as young children, thyroid cancer patients, pregnant women, and frail patients.3
WEIGHT CHANGES
As mentioned, thyroid medications are weight-based, and big changes in weight can lead to changes in thyroid function studies. It is the lean body mass, rather than total body weight, that will affect the thyroid requirement.3 A quick review of the patient’s weight history needs to be done when thyroid function test results have changed.
GASTROINTESTINAL DISTURBANCES
Hypothyroid medications are absorbed in the small intestine, and gastric acidity levels have an impact on absorption. Any acute or chronic conditions that affect these areas can alter medication absorption quite significantly. Commonly encountered diseases and conditions are H pylori–related gastritis, atrophic gastritis, celiac disease, and lactose intolerance. Treating these diseases and conditions can improve medication absorption.
I went through the list with the patient, but there was no applicable scenario. I adjusted his medication but went ahead and tested for tissue transglutaminase antibody IgA to rule out celiac disease; results came back mildly positive. The patient was referred to a gastroenterologist, who performed a small intestine biopsy for definitive diagnosis. This revealed “severe” celiac disease. A strict gluten-free diet was started, and the patient’s LT4 dose was adjusted, with regular monitoring, down to 150 μg/d.
Common symptoms of celiac disease include bloating, abdominal pain, and loose stool after consumption of gluten-containing meals. It should be noted that this patient denied all these symptoms, even though he was asked specifically about them. After he started a gluten-free diet, he reported that he actually felt “very calm” in his abdomen and realized he did have symptoms of celiac disease—but he’d had them for so long that he considered it normal. As is often the case, presence of symptoms would raise suspicion ... but lack of symptoms (or report thereof) does not rule out the disease.
CONCLUSION
Most patients with hypothyroidism are fairly well managed with relatively stable medication dosages, but there are subsets of patients who struggle to maintain euthyroid range. The latter require frequent office visits and dosage changes. Carefully reviewing the list of possible reasons for thyroid level changes can improve stability and patient quality of life, prevent complications of fluctuating thyroid levels, and reduce medical costs, such as repeated labs and frequent clinic visits.
REFERENCES
1. Garber JR, Cobin RH, Gharib H, et al; American Association of Clinical Endocrinologists and American Thyroid Association Taskforce on Hypothyroidism in Adults. Clinical practice guidelines for hypothyroidism in adults [published correction appears in Endocr Pract. 2013;19(1):175]. Endocr Pract. 2012;18(6):988-1028.
2. Sabate E. Adherence to Long-Term Therapies: Evidence for Action. Geneva, Switzerland: World Health Organization; 2003.
3. Jonklaas J, Bianco AC, Bauer AJ, et al; American Thyroid Association Task Force on Thyroid Hormone Replacement. Guidelines for the treatment of hypothyroidism. Thyroid. 2014;24(12):1670-1751.