Enhancement of radioiodine uptake in hyperthyroidism with hydrochlorothiazide: a prospective randomised control study

The aim of this study was to determine whether hydrochlorothiazide (HCTZ) could improve radioiodine uptake in low-uptake hyperthyroid patients. Eighteen hyperthyroid patients with low 3-h and 24-h iodine-131 uptake were recruited to the study. Eleven patients were assigned to the HCTZ group, and seven to the control group. Two weeks after the first, baseline uptake study, a second uptake study was performed. Patients in both groups had a low-iodine diet after the first uptake study. In the HCTZ group, 50 mg of HCTZ was administered twice a day for 5 days prior to the second uptake study. Improvement in uptake at 3 and 24 h in the second uptake study, as compared with the baseline study, was assessed within and between groups. In the control group, compared with the baseline study there was a significant improvement in uptake at 3 h ( P=0.03) but a non-significant improvement at 24 h ( P=0.07). In the HCTZ group, significant improvements were observed at both 3 h ( P=0.0005) and 24 h ( P=2.28 x 10(-5)). Patients in the HCTZ group had statistically greater improvement in uptake at both 3 h and 24 h compared with the control group ( P=0.003 and 0.0008, respectively). There was a 7.18-fold average improvement in uptake in the HCTZ group at 24 h, compared with only a 1.33-fold improvement in the control group. Administration of HCTZ significantly improves 24-h radioiodine uptake in high-iodide pool, low-uptake hyperthyroid patients compared with patients who have received a low-iodine diet alone.