Not all hypothyroid patients are created equal?

For a majority of hypothyroid patients, levothyroxine (brand names include: Synthroid, Levoxyl) alone is enough to feel well. However, for some individuals, symptoms may persist despite taking commercially available medications and achieving normalization of TSH and free T4 levels.

Several genetic differences have been identified in individuals, which impair these patients and prevent them from converting T4 to the active thyroid hormone, T3. A recent study demonstrated that between 12% - 36% of the population have a genetic variation which makes it difficult for them to convert T4 to T3.1 Additionally, another study reported a clear preference for combination therapy (T4/T3) over treatment with T4 only.2 For these patients, a combination of T4 and T3, compounded into a single extended release capsule, may be what they have been searching for all along.

Desiccated Porcine Thyroid

Products that contain desiccated thyroid include Armour Thyroid, Westhroid, and Nature-Throid. Many patients turn to these products when they feel that T4 alone is not helping them with their hypothyroid symptoms. Dessicated porcine thyroid may help to make some patients feel better but there are a few problems that have been observed with its use:

  • More than 99% of desiccated thyroid powder is pork thyroid gland, of which its specific contents have not been identified nor standardized regarding the content of T4 and T3.
  • It contains a standardized ratio of T4:T3 of 4.2:1. This is the normal ratio of T4:T3 that a pig thyroid naturally produces, not a human.
  • A fixed ratio does not allow for individual differences in T4/T3 conversion.
  • Not available in an extended release dosage form, resulting in two to three times daily dosing.

Compounded T4/T3 Combination

A T4/T3 combination prepared by a compounding pharmacy may have certain advantages for patients. The ratio of T4 to T3 may be customized to each individual patient based on lab results and symptoms. Also, a compounded T4/T3 combination may be formulated into an extended release capsule to account for the short half life of T3. Therefore, the combination T4/T3 capsule has the ability to be conveniently dosed only once a day.




References:

1 McAninch EA, Jo S, Preite NZ et al. Prevalent polymorphism in thyroid hormone-activating enzyme leaves a genetic fingerprint that underlies associated clinical syndromes. J Clin Endocrinol Metab. 2015 Mar;100(3):920-33.
2 Nygaard B, Jensen EW, Kvetny et al. Effect of combination therapy with thyroxine (T4) and 3,5,3′-triiodothyronine versus T4 monotherapy in patients with hypothyroidism, a double-blind, randomised cross-over study. Eur J Endocrinol. 2009 Dec;161(6):895-902.