Case ReportTablet Levothyroxine (L-T4) Malabsorption Induced by Proton Pump Inhibitor; A Problem that was Solved by Switching to L-T4 in Soft Gel Capsule
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INTRODUCTION
The list of drugs that can interfere with levothyroxine (L-T4) intestinal absorption is growing (1). Drugs impair tablet L-T4 absorption either by increasing gastric pH and hindering tablet dissolution or by physically sequestering L-T4. In both cases, the permeability of L-T4 through the intestinal epithelium is impaired (1). Among the drugs that increase the gastric pH, proton pump inhibitor (PPIs) act by inhibiting the H+/K+ ATPase pump in gastric parietal cells. In 2011 in the U.S., L-T4
CASE REPORT
A 48-year Caucasian woman was diagnosed, prior to our observation, with Hashimoto’s thyroiditis and associated subclinical hypothyroidism (serum thyroid-stimulating hormone [TSH] = 6.8 to 9.6 mU/L, normal values 0.27-4.2; free triiodothyronine [FT3] = 3.47 pmol/L, normal values 3.07-6.76; free thyroxine [FT4] = 15.70 pmol/L, normal values 12.0-22.0; thyroid peroxidase antibody [TPOAb] = 420.5 IU/ml, normal values < 34.0). Although the patient had a normally sized thyroid with the typical
DISCUSSION
The soft gel capsule is pearl-shaped and contains L-T4 dissolved in glycerin and covered with a soft gelatin protective shell. This formulation renders L-T4 less available for quick mixing with fluids/solids capable of sequestering L-T4 in the gastrointestinal tract. We recently demonstrated that the soft gel capsule is resistant to interference of L-T4 absorption by coffee, taken concomitantly or shortly after L-T4 ingestion (14). Other authors have documented the same coffee-resistance for
CONCLUSIONS
Because the administration of both PPIs and L-T4 are quite common, it is likely that cases of L-T4 malabsorption due to PPI are overlooked. The chemical structure and pharmacokinetics of soft gel capsules render them more resistant to the adverse effects on L-T4 absorption exerted by PPIs. More studies are needed to verify whether L-T4 contained in soft gel capsules are more refractory to the impaired L-T4 absorption caused by other drugs.
DISCLOSURE
The authors received from IBSA Institut Biochimique (Lugano, Switzerland) novel L-thyroxine formulations for conducting the clinical study.
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