Intestinal absorption and buccal absorption of liquid levothyroxine

Excerpt

Hypothyroidism is a common life-long dysfunction, as its prevalence in the adult population is approximately 5% [1]. Levothyroxine (L-T4) alone is recommended for the replacement therapy [2]. On the average, 70% of the L-T4 ingested as a tablet is absorbed, and an acid intragastric pH is required for its optimal dissolution [3, 4]. L-T4 therapy is monitored by periodic assays of serum thyrotropin [thyroid-stimulating hormone (TSH)] to ensure that TSH reaches and maintains target levels. Except for the pregnancy setting, TSH target levels are ≤4.12 mU/L [2]. A number of conditions/diseases of the digestive system and drugs/supplements/beverages cause L-T4 malabsorption, resulting in failure of serum TSH to be normalized [3‐5]. The rate of undertreated hypothyroidism (also known as resistant or refractory hypothyroidism) is around 20% [4]. The correction of resistant hypothyroidism or obtaining lower levels of TSH in the absence of refractory hypothyroidism is possible by switching the tablet to new formulations (soft gel capsule, liquid solution) [6‐13]. …