The consequences of under treatment by thyroxine therapy caused by malabsorption

[diogenes]

This paper shows the negative implications for a lack of sufficient T4 absorption on treatment. Note the modest TSH rises that accompanied this. Paper downloadable/

Journal of Clinical & Translational Endocrinology

Benvenga et al

Volume 16, June 2019, 100189

doi.org/10.1016/j.jcte.2019...

A minimum of two years of undertreated primary hypothyroidism, as a result of drug-induced malabsorption of l-thyroxine, may have metabolic and cardiovascular consequences

Abstract

Objective

Cross-sectional studies have reported that TSH above or close to the upper normal limit correlates with unfavorable metabolic and cardiovascular outcomes. Certain medications impair intestinal absorption of levothyroxine (L-T4), resulting in undertreated hypothyroidism (viz. failure of serum TSH to reach target levels, if hypothyroidism is primary).

Further to evaluating the magnitude of sub-optimally treated primary hypothyroidism as a result of co-ingestion of those medications, we wished to ascertain whether the above complications would occur during a low number of years under polypharmacy.

Method

In this retrospective study in collaboration with 8 family physicians, we enrolled adults with primary hypothyroidism under L-T4 therapy that, for 2 years minimum, was not associated with those medications (non-exposure, baseline) and that, for another 2 years minimum, it was (exposure). Outcomes were serum levels and proportions of serum TSH levels >4.12 mU/L, and proportions of complications. Complications were aggravation of pre-existing or de novo onset of any of metabolic syndrome, impaired fasting glycemia (IFG), diabetes mellitus, dyslipidemia, hypertension, coronary heart disease (CHD), cerebrovascular disease (CVD).

Result

A total of 114 patients were enrolled. Duration of exposure to the interfering medication was 32.1 ± 6.9 months (median 31; range 24–55). Compared with non-exposure, the exposure period resulted in greater TSH levels (2.81 ± 3.62 [median 1.79] vs 1.27 ± 1.34 [median 0.93], P = 2.2 × 10−20) and proportions of values >4.12 mU/L (18.5% vs 4.7%, P = 1.2 × 10−7). Seventy-six patients (67%) had complications, whose rates of TSH >4.12 mU/L were greater than in the 36 complication-free patients (22% vs 11%, P = 0.018).

Conclusion

During a median period of 31 months, there are relevant consequences for L-T4 treated adult hypothyroid patients resulting from hyperthyrotropinemia caused by medications impairing L-T4 absorption. This should be taken into account by future guidelines on hypothyroidism management.

[Charlie-Farley]

Brilliant, thank you 😊👍

Have you noticed through reading lived experience posts how people who have been mucked about with their dosing by Doctors chasing TSH can be permanently impaired? Never getting back to the sweet spot when initially treated? Going back to the same level medication after the doctor (if they are lucky) realises, despite everything they ‘know’, dosing by TSH hasn’t worked.

Could this be that by the time they are returned to the original therapeutic dose, additional damage has occurred which is now being medicated and the patient is permanently impaired. I know it’s anecdotal and there is no data as such to investigate further, but I can’t help but wonder……..

[tcpace]

Does this not have implications for people who are not treated because they are sub-clinical? Current practice is merely to monitor TSH and only treat when TSH > 10. So are sub-clinical patients at higher risk for cardio and metabolic problems?

[knitwitty in reply to tcpace]

I was thinking exactly the same thing. There are countless people on here ( me included ) who were denied treatment for "sub clinical" hypothyroidism for years, I dread to think what the long term effects are for those of us who have been, a nd continue to be , ignored by many GP's and even Endocrinologists.

[helvella Administrator Thyroid UK]

Thank you, diogenes.

Seems to have been quite a thoughtful team who wrote that.

Can't say it surprises me that the identified effects occur. But having it written up properly in a paper is worth a lot more than a fleeting thought in my mind.