Intramuscular and subcutaneous levothyroxine: success in treating refractory hypothyroidism

Refractory hypothyroidism often poses a clinical problem, as treatment regimens are difficult to individualise to the patient and the feasibility of its delivery is difficult to organise within a healthcare system. We present a patient who became intolerant of intramuscular (IM) levothyroxine (LT4) after 18 years of treatment; thus, subcutaneous (SC) LT4 was initiated.

A 13-year-old female with newly diagnosed hypothyroidism remained hypothyroid despite escalating doses of oral LT4 and LT3. Thyroxine malabsorption was further suggested by nasogastric administration of LT4, whereby high-dose thyroxine administration resulted in only a 2.8 pmol/L increase in free T4 level (normal >5.14 pmol/L). She eventually achieved long-term euthyroid status at the age of 18 with fortnightly IM LT4 alongside oral LT4 and LT3. This was maintained for 18 years. Unfortunately, scar tissue developed around injection sites, resulting in increased pain and difficulty in administration. SC LT4 was trialled with success, and she has remained euthyroid for the last 6 years with self-administration and minimal side effects.

Refractory hypothyroidism often presents a challenge for clinicians, both for diagnosis and management. We discuss a patient with the longest follow-up to date within the published literature for both IM and SC LT4 for patient-administered treatment of refractory hypothyroidism and review the literature on alternative formulations available.