Radioiodine uptake and thyroid hormone levels on or off simultaneous carbimazole medication: a prospective paired comparison.
OBJECTIVE
To allow radioiodine (RAI) treatment in patients with need for anti-thyroid drug medication and low RAI uptakes we investigated the feasibility of discontinuing carbimazole for 3 days to enhance the RAI uptake without concurrent exacerbation of hyperthyroidism.


METHODS
We prospectively investigated RAI dynamics and thyroid hormone concentration in 12 patients with low RAI uptake (<30%) under simultaneous carbimazole medication and 3 days after discontinuation. At both time points fT(4), T(3) and TSH were monitored.


RESULTS
Discontinuation of carbimazole for 3 days led to a significant increase of RAI uptake in all patients. We found an enhancement up to 4.9-fold compared to the measurement on carbimazole. The mean RAI uptake increased from 15.2 +/- 4.4% to 50.1 +/- 15.5% (p<0.001). The intrapersonal radioiodine half-life increased from 4.2 +/- 1.6 days to 5.4 +/- 0.7 days (p = 0.13). Mean thyroid hormone concentration was not affected by the three day withdrawal of anti-thyroid drugs and no patient suffered from an aggravation of biochemical hyperthyroidism.


CONCLUSIONS
A withdrawal of carbimazole for 3 days is long enough to provide sufficiently high RAI uptakes for RAI treatment in patients with low RAI uptakes and short enough to avoid the risk of exacerbation of hyperthyroidism.
Walter
M A
MA
Institute of Nuclear Medicine, University Hospital, Petersgraben 4, 4031 Basel, Schweiz. m.a.walter@gmx.net
Christ-Crain
M
M
Müller
B
B
Müller-Brand
J
J
D000328:Adult; D000368:Aged; D013956:Antithyroid Agents / Q000493:pharmacokinetics / Q000627:therapeutic use; D001692:Biological Transport; D002231:Carbimazole / Q000493:pharmacokinetics / Q000627:therapeutic use*; D003131:Combined Modality Therapy; D005260:Female; D006111:Graves Disease / Q000188:drug therapy* / Q000532:radiotherapy*; D006801:Humans; D007457:Iodine Radioisotopes / Q000493:pharmacokinetics / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D011877:Radionuclide Imaging; D013960:Thyroid Function Tests; D013961:Thyroid Gland / Q000000981:diagnostic imaging; D014463:Ultrasonography
D013956:Antithyroid Agents; D007457:Iodine Radioisotopes; D002231:Carbimazole