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

Abstract

unselected thyrotoxic patients were prescribed 200 MBq radioactive iodine ( 131 I). None of these patients received a thionamide such as carbimazole or propylthiouracil within two weeks of treatment or subsequently. Symptom relief was achieved using 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 131 I between 1996 and 2001 gave comparable results. The failure rate after a single 200 MBq 131 I dose was significantly lower than that previously published where 185 MBq 131 I 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. KEY WORDS: radioiodine, thionamide, thyrotoxicosis IntroductionRadioactive iodine ( 131 I) therapy has been used for over 60 years to treat patients with thyrotoxicosis, 1 and in some departments it accounts for 79% of referrals for definitive treatment of adults with this condition. 2 Guidelines formulated by the Royal College of Physicians in 1995 recommended that doses of 300-800 MBq 131 I should be used, and that thionamide therapy, such as carbimazole or propylthiouracil, should be given to most patients unless the thyrotoxicosis was mild. 3 Lower doses of 131 I were regarded as inadequate, but the outcome in those studies had been compromised by the concomitant use of thionamides, 4-7 which have been shown to reduce the effectiveness of 131 I by up to 44%. 8 Doses of 520-555 MBq of 131 I will achieve remission rates between 91 and 94% at one year, 9-11 but a clear statement regarding an outcome target is lacking.It is, however, important to minimise the potential therapeutic hazard of exposing patients and the environment to non-essential radiation. In the light of these considerations, we examined the efficacy of a fixed dose of 200 MBq 131 I compared with larger doses, prescribed in our department over the last five years, for thyrotoxic patients whose symptoms were modified by beta-adrenergic blocking drugs alone, and compared our results with the published data. Patients and methodsFrom 1996 to June 2001 all thyrotoxic patients referred to the Endocrine Department, and who subsequently received 131 I treatment, were entered on our thyroid register. Patients presenting with subacute thyroiditis and those in whom the free thyroxine (FT4) was 22 pmol/l or the thyroidstimulating hormone (TSH) was detectable, were not considered suitable candidates for 131 I treatment. All patients had been given an information package and at a subsequent visit those considered suitable were able to choose from three options: treatment with a thionamide, surgery or 131 I.The dose of 131 I prescribed was either 200 MBq or 250-400 MBq. This was given as a 131 I capsule. The majority of the patients for who...

The influence of antithyroid drug discontinuation to the therapeutic efficacy of 131 I in hyperthyroidism

“…Several studies that compared efficacy of different doses of radioactive iodine included doses of 200 MBq, 259 MBq, less than 370 MBq, or greater than 370 MBq were done. [ 16 17 18 ]…”

“…Several studies that compared efficacy of different doses of radioactive iodine included doses of 200 MBq, 259 MBq, less than 370 MBq, or greater than 370 MBq were done. [16][17][18] Imseis et al evaluated the influence of PTU and MMI to therapeutic efficacy of 131 I in hyperthyroidism that pretreated with. The study concluded that the cure rate of 131 I therapy was significantly reduced after pretreatment with PTU, even when it was discontinued for 5-55 days before radioactive iodine therapy.…”