Endocrine Abstracts

Armour thyroid is desiccated porcine extract which is a historical treatment for hypothyroidism. It contains both L-thyroxine and liothyronine. Each grain (60 mg) contains 38 μg of L-thyroxine and 9 μg liothyronine. Since the 1960’s its use has been superseded by L-thyroxine. Due to limited clinical effectiveness studies, it is not licensed for use in the United Kingdom. We present a case of Armour thyroid use in pregnancy at patient’s request following refusal to switch to L-thyroxine.

Case: 33 year old lady was referred to our joint antenatal-endocrine clinic at 18 weeks gestation. She was initially diagnosed with primary hypothyroidism in 2010 with strongly positive TPO antibodies 6 weeks following her first pregnancy. She was commenced on 125 μg of L-thyroxine. Treatment with L-thyroxine failed to abate her symptoms and as a result she commenced a self-prescription with three grains of armour thyroid in 2011. She had a subsequent pregnancy which ended with a miscarriage at 6 weeks gestation whilst on armour thyroid. In her third pregnancy she increased her dose of armour thyroid to three and a half grains at booking. Her TSH was suppressed throughout gestation at <0.02 mU/l (0.20–4.00 mU/l). Her average free T₄ was 12.4 pmol/l (9.0–19.0 pmol/l) and free T₃ 6.15 pmol/l (2.5–5.7 pmol/l). The entire course pregnancy course was uneventful with foetal normal anatomy and interval scans. She delivered a live male foetus at 40 weeks with an unremarkable baby check and heel prick screen.

Discussion: Armour thyroid is not recommended for treatment of hypothyroidism in the UK, this is more so in the context of pregnancy. There are safety concerns regarding excessive amounts of T₃ relative to T₄, which is inconsistent with normal physiology. In pregnancy, the potential risk to both mother and foetus are unknown. Moreover compared to L-thyroxine, it is not regarded as a pure preparation of thyroid hormone. Our patient’s TSH was suppressed throughout the pregnancy, despite being fully aware of the potential risks. Although the outcome was uneventful, this was an ethico-legal challenge balancing patient expectation against recommended practice. We do not recommend its use in pregnancy.