The efficacy of low-dose radioactive iodine without a thionamide in the treatment of thyrotoxicosis.

Between 1999 and June 2001, 55 unselected thyrotoxic patients were prescribed 200 MBq radioactive iodine (131I). None of these patients received a thionamide such as carbimazole or propylthiouracil within two weeks of treatment or subsequently. Symptom relief was achieved using beta blockers alone. Remission at one year was achieved in 84% of these patients and of these 62% were hypothyroid and taking thyroxine. Within this time, re-treatment of those who remained thyrotoxic achieved an overall success rate at one year of 95%. The outcome of 164 similar patients prescribed 250-400 MBq 131I between 1996 and 2001 gave comparable results. The failure rate after a single 200 MBq 131I dose was significantly lower than that previously published where 185 MBq 131I and thionamides had been used. Our low-dose strategy has the potential for halving the radiation exposure to the patient and the environment, when compared with the ablative strategies in common use.