A randomised study of two antithyroid drug treatment regimens in young people with thyrotoxicosis 

We are delighted to have financially supported this important study through our 2008 BTF Research Award. The study looked at how best to use antithyroid drugs (ATD) in young people with thyrotoxicosis* (an overactive thyroid gland). The final report was published in the European Journal of Endocrinology in autumn 2020  


Around 120 young people (under the age of 16 years) present with thyrotoxicosis every year. Most will be treated initially with antithyroid drugs or ATD for short (usually Carbimazole, occasionally Propylthiouracil). ATDs reduce the amount of thyroid hormone your body produces with the aim of getting your thyroid hormone levels under control. 

ATD can be given in one of two ways: 

  • 'Block and replace' treatment (BR). This is where thyroid hormone production by the overactive thyroid gland is switched off completely by ATD and thyroxine is then added in a 'replacement' dose. 
  • 'Dose titration' treatment (DT). This is where the dose of ATD is adjusted so that hormone production by the overactive gland is reduced to normal. 

Both BR and DT therapy have potential advantages and disadvantages.  

The potential advantages of BR treatment include: 

  • More stable thyroid function tests 
  • A reduced number of blood tests and visits to hospital 
  • A reduced likelihood of the over-activity returning when the ATD is stopped 

The potential advantages of the DT approach include: 

  • Fewer side effects with a lower ATD 
  • Improved compliance on one rather than two medications because the DT approach involves taking just ATD and not thyroxine as well 

Study aims 

The primary aim was to establish what the advantages and disadvantages of the BR and DT approaches are in this age group. Researchers particularly sought to establish which treatment method provides more stable biochemical control – in particular the amount of time spent with normal TSH levels. This was felt to be particularly important as young people tend to be on ATDs for a long period of time. 


The randomised trial studied 81 patients aged between 2 and 17, who had recently been diagnosed with thyrotoxicosis. Patients were treated for three years across 15 different UK centres. 40 of the patients were treated with BR, the other 41 received DT treatment. Patients were monitored patients every four weeks for the first four months, then every 2 months and then every 3 months. The main outcome was the proportion of patients’ Thyroid Stimulating Hormone (TSH) levels that were within the reference range. After the three year treatment period the young people were monitored to determine whether they had achieved remission or whether further treatment was needed 


A greater proportion of DT patients than BR patients had serum TSH with reference range at the end of the study: 63.8% versus 60.2%. The proportion of patients with FT4 (thyroxine) within reference range was also greater in the DT group (85.7%) compared with 79.2% in the BR group. 

6 of the BR patients and 10 of the DT patients were in remission at the end of the four years.  


The randomised trial showed no evidence to suggest BR offers improved biochemical stability over DT in young people with thyrotoxicosis. It did not show any evidence to refute current guidelines which recommend that most young people with thyrotoxicosis should be treated with DT. 

What will this mean for patients? 

Patients, families and healthcare professionals can be given more accurate information about how best to use ATD with more objective detail about the relative risks and benefits of each respective treatment. 

Read the European Journal of Endocrinology report 

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