Treatment of Thyroxine Malabsorption

Abstract

The aim of the case study was to report the successful use of intramuscular levothyroxine (L-T 4 ) in two patients with profound oral L-T 4 malabsorption. We present two cases of patients who remained hypothyroid despite very high oral doses of L-T 4 . In both cases, poor L-T 4 absorption was documented with an absorption study. Intramuscular L-T 4 injections were initiated in both cases and doses were titrated to achieve normalization of thyroid stimulating hormone (TSH) and free thyroxine (free T 4 ). Additionally, after achieving euthyroidism for a period of time, each patient was able to successfully transit back to oral administration of L-T 4 . Synthetic oral L-T 4 is the drug of choice for replacement therapy in patients with hypothyroidism. Whenever euthyroidism cannot be achieved despite escalating L-T 4 doses, the presence of interfering factors must be considered. These factors include low patient compliance or reduced L-T 4 absorption due to other dietary factors, concomitant medication use or gastrointestinal disease. Furthermore, severe hypothyroidism itself may impair absorption, presumably due to edema of the small bowel mucosa. Parenteral L-T 4 has been shown to be an effective method of replacing thyroid hormone in those patients with apparent thyroid hormone malabsorption. However, there is no consensus or guidelines available to aid physicians in the use of parenteral L-T 4 . In patients with hypothyroidism despite large doses of levothyroxine, physicians should consider thyroid malabsorption once compliance and interfering medicines have been ruled out. In these patients, if no correctable interfering factor is identified, intramuscular replacement appears to be an effective alternative.

Levothyroxine Absorption Test in the management of a patient with persistent hypothyroidism

“…The improvement of doctor-patient relationship is very important 2 . To improve the state of hypothyroidism two main prescriptions are possible: supervised weekly thyroxine replacement (the total weekly dose of LT4 given once per week) or parenteral administration (intramuscular or intravenous) of levothyroxine 3,14 . Once weekly administration of LT4 is safe and efficient and therefore a possible alternative to customary daily therapy.…”

“…Synthetic thyroxine has been used to treat hypothyroidism successfully since 1927 2 . The optimal daily dose of 1.6-1.8 ug/body weight (kg) per day of levothyroxine (LT4) is an appropriate replacement dose [1][2][3] . The absorption of oral LT4 occurs mostly in the jejunum and ileum (60-80% of the ingested dose) [3][4][5][6] .…”

“…The optimal daily dose of 1.6-1.8 ug/body weight (kg) per day of levothyroxine (LT4) is an appropriate replacement dose [1][2][3] . The absorption of oral LT4 occurs mostly in the jejunum and ileum (60-80% of the ingested dose) [3][4][5][6] . It is maximal when the stomach is empty and takes place within the first 3 hours of ingestion 2 .…”

“…For patients who require larger doses of LT4 than expected, the underlying cause can be challenging to determine 2 . Several factors must be considered: low patient compliance, reduced LT4 absorption from interfering dietary factors and medications, or gastrointestinal disorders contributing to malabsorption 7 . The most common cause of mal-absorption is poor or non-compliance with oral LT4 treatment by the patient 8 .…”

Levothyroxine absorption test in the management of a patient with persistent hypothyroidism

“…The improvement of doctor-patient relationship is very important 2 . To improve the state of hypothyroidism two main prescriptions are possible: supervised weekly thyroxine replacement (the total weekly dose of LT4 given once per week) or parenteral administration (intramuscular or intravenous) of levothyroxine 3,14 .…”