title: Outcome of radioiodine therapy without, on or 3 days off carbimazole: a prospective interventional three-group comparison.
abstract: OBJECTIVE
  Carbimazole ameliorates hyperthyroidism but reduces radioiodine uptake and adversely affects the outcome of simultaneous radioiodine therapy. We explored whether withdrawal of carbimazole for 3 days can restore the outcome of radioiodine treatment without concurrent exacerbation of hyperthyroidism. By generating three groups with comparable radioiodine uptake, we also investigated whether the effect of carbimazole depends on the radioiodine uptake.
  
  
  METHODS
  Stratified by a radioiodine uptake >30%, 227 consecutive adult patients were prospectively assigned to radioiodine therapy (target dose 200 Gy) without, on or 3 days off carbimazole. Patients were clinically (Crooks-Wayne score) and biochemically (T(3), fT(4), TSH) followed up after 3, 6 and 12 months. Primary endpoint was outcome 12 months after radioiodine therapy.
  
  
  RESULTS
  A total of 207 patients completed follow-up (toxic nodular goitre, n=117; Graves' disease, n=90). The overall success rate was 71.5%. Patients without and 3 days off carbimazole had similar biochemical (81.4% and 83.3%, respectively; p=0.82) and clinical outcomes [median (range) Crooks-Wayne score 0 (0-16) and 1 (0-10), respectively; p=0.73], which were both higher than in patients on carbimazole [42.6%, p<0.001; Crooks-Wayne score 3 (0-30), p<0.03]. Time to achieve cure was delayed on carbimazole. No changes in thyroid hormone levels occurred after 3 days' discontinuation of carbimazole. Logistic regression revealed that all observed cure rates were independent of entity, sex, age, thyroid volume, radioiodine uptake, radioiodine half-life, fT(4), T(3) and TSH.
  
  
  CONCLUSIONS
  Patients under carbimazole treatment can be referred for radioiodine therapy after withdrawal of carbimazole for only 3 days. Three days of carbimazole withdrawal is long enough to restore the success of radioiodine therapy and short enough to avoid the risk of exacerbation of hyperthyroidism.
authors.affiliation: Institute of Nuclear Medicine, University Hospital, Petersgraben 4, 4031, Basel, Switzerland. m.a.walter@gmx.net
authors.forename: Martin A
authors.initials: MA
authors.lastname: Walter
authors.forename: Mirjam
authors.initials: M
authors.lastname: Christ-Crain
authors.forename: Christian
authors.initials: C
authors.lastname: Schindler
authors.forename: Jan
authors.initials: J
authors.lastname: Müller-Brand
authors.forename: Beat
authors.initials: B
authors.lastname: Müller
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D013956:Antithyroid Agents / Q000008:administration & dosage; D002231:Carbimazole / Q000008:administration & dosage*; D017024:Chemotherapy, Adjuvant / Q000379:methods; D004334:Drug Administration Schedule; D005260:Female; D006801:Humans; D006980:Hyperthyroidism / Q000175:diagnosis / Q000628:therapy*; D007457:Iodine Radioisotopes / Q000008:administration & dosage*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D019275:Radiopharmaceuticals / Q000008:administration & dosage; D016896:Treatment Outcome
chemical_list: D013956:Antithyroid Agents; D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D002231:Carbimazole