Daily Intramuscular Levothyroxine in Refractory Hypothyroidism and Malabsorption

In patients with hypothyroidism, levothyroxine (LT4) monotherapy is the standard treatment; however, when standard therapy is ineffective, alternative approaches including liquid LT4, desiccated thyroid extract, LT4/liothyronine combinations, or injectable LT4 can be considered.

A 55-year-old Caucasian woman with a history of Hashimoto thyroiditis, diagnosed during her first pregnancy in 1989, was controlled on 125 mcg of Synthroid daily until undergoing Roux-en-Y gastric bypass in 2004. Several years following gastric bypass surgery, she developed persistent hypothyroidism with increased serum thyroid-stimulating hormone (TSH) levels, low free thyroxine levels, and symptoms including fatigue, brain fog, constipation, cold intolerance, hair loss, dry skin, and delayed wound healing. Despite trials of various high-dose oral thyroid hormone regimens-including Tirosint (750 mcg daily), Synthroid (200 mcg daily), a combination of LT4 (175 mcg) and triiodothyronine (10 mcg), and Armour (150 mg daily)-her TSH level remained elevated. Thyroid hormone absorption tests revealed significant reduction in absorption: (1) 9% for Tirosint (1050 mcg), (2) 50% for Synthroid (1000 mcg), (3) 47% for Armour thyroid (600 mcg), and (4) 69% for sublingual LT4. Given her refractory hypothyroidism, intramuscular (IM) LT4 100 mcg daily was started, leading to normalization of TSH level and resolution of symptoms.

Our manuscript highlights the importance of considering alternative therapies for hypothyroidism, including IM LT4 either daily or weekly, when the oral routes are not adequately bioavailable to normalize TSH levels and resolve symptoms. This is the first case report of successful treatment of uncontrolled hypothyroidism with daily IM LT4 in an outpatient setting. Further studies are needed.