Description
Studies consistently show that as many as 40% of patients with hypo- or hyper-thyroidism are not well managed by physicians. These studies each used thyroid-stimulating hormone (TSH) as the clinical marker of thyroid dysfunction. Studies have also shown that the clinical consequences of abnormal TSH levels include cardiovascular and lipid risks; miscarriage, fetal death and lower IQs; and particular risks for patients with cancer.

There are several reasons for an abnormal TSH level: patient compliance, factitious ingestion, a change in diet or the addition of confounding medications, etc.

Another factor that may disrupt the stability of thyroid patients' TSH levels is the introduction of generic levothyroxine (LT₄) preparations into the marketplace. As you know, bioequivalence studies are required for a generic to be deemed interchangeable (i.e., therapeutically equivalent) with other products. Two key issues that arise when bioequivalence (BE) studies are conducted on LT₄ products involve the use of T4 as the BE marker and the endogenous levels of T4 in study subjects.

Furthermore, a 2004 study showed that BE standards cannot tell the difference between doses that differ by as much as 12.5% to 25%. Therefore patients whose LT₄ preparations are changed may be at risk for change in both TSH and T4 levels.

In the case of LT₄ products, no studies have been done to evaluate the effectiveness of generics on stabilizing TSH levels. Therefore, the quality of these products is not at stake.

What is at stake is optimizing patient care. To provide the best possible care, it is imperative that physicians and pharmacists work together to ensure patients are maintained within the tight TSH required to avoid clinical issues. This can be accomplished through physician monitoring of patients habits and TSH levels, and more critically, maintaining patients on one LT₄ preparation from refill to refill.