Endocrine Abstracts

We report a case of a 57-year-old woman with profound uncontrolled hypothyroidism diagnosed in 1999. At her first Endocrine clinic visit in 2015, her TSH level was 93.4 mU/l with FT4 level of 4.8 pmo/l. Despite increasing her Levothyroxine dose, her TSH level remained persistently above 80 mU/l with a low FT4. She had a gastroscopy and coeliac screening which were non-significant. Triiodothyronine 10 mg was added to Levothyroxine 100 mg once daily in October 2015. However, she remained unwell clinically with fatigue and under-replaced with her TSH remaining elevated at 83 mU/l with a low T4 (3.5 pmo/l) and T3 (2.7 pmo/l). Thyroid absorption test showed no variation of TSH levels, highlighting no active absorption of Levothyroxine tablets despite having tried various tablet formulations. She declined to take natural thyroid extract. In December 2019, a fresh endocrine re-assessment following re-referral by her GP identified a likely allergic reaction to Levothyroxine tablet formulations as she reported facial swelling within 20 minutes after taking her tablets. She was initiated on liquid form of Levothyroxine 100 mg with Liothyronine 10 mg tablets. The patient reported disappearance of her previous allergic reaction on liquid Levothyroxine. Unfortunately, her prescription was not renewed by her GP due to the higher cost. Following re-issue via hospital prescription, her TSH level gradually improved to 0.72 mU/l with her latest FT4 at 24.6 pmo/l. In assessing uncontrolled hypothyroidism, a careful history is extremely important as well as a good understanding of the pharmacology of different Levothyroxine formulations. This patient not only had an allergy to different Levothyroxine tablet excipients, but also a resulting absorption issue. One should think about the option of alternative Levothyroxine liquid formulation which has a faster rate of absorption and time to peak concentration over tablets.