The effect of formulation on reduced radioiodide thyroid uptake.
This investigation compared in vitro dissolution profiles from sodium iodide capsules with radioiodide thyroid uptake in patients with thyroid abnormalities, using sodium iodide capsules prepared with a formulation exhibiting complete release of radioiodide in vitro and a formulation exhibiting incomplete release.


METHODS
In vitro dissolution profiles for radioactive sodium iodide capsules with 2 different formulations were determined using the U.S. Pharmacopeia (USP) XXIV dissolution test. The 2 formulations studied in vitro were sodium phosphate dibasic powder with 1% magnesium stearate and calcium phosphate dibasic powder with 3% magnesium stearate. The thyroid uptake of radioiodide from capsules exhibiting complete release or incomplete release of radioiodide was determined in patients with thyroid disorders.


RESULTS
In the dissolution studies, by 20 min after initiation of the test, >95% of the radioactive iodide was released from capsules of sodium phosphate dibasic powder. The capsules of calcium phosphate dibasic powder reached 75% at 65 min, with no further release occurring thereafter. In the in vivo studies, the mean thyroid uptake at 1 h for sodium phosphate dibasic powder with 1% magnesium stearate (complete-release formulation) was 12.7%, compared with 9.3% for calcium phosphate dibasic powder with 3% magnesium stearate (incomplete-release formulation) (P < 0.05). At 24 h, the value was 56.6% for the complete-release formulation, compared with 50.3% for the incomplete-release formulation (P < 0.01, Wilcoxon signed rank test). At 1 h, the abdominal activity for the complete-release formulation was 3.4%, compared with 8.8% for the incomplete-release formulation (P < 0.01). At 24 h, the value was 0.4% for the complete-release formulation, compared with 1.0% for the incomplete-release formulation (P < 0.01).


CONCLUSIONS
The data suggest that the incomplete dissolution profile observed in vitro may correlate with reduced bioavailability of radioiodide in vivo. The USP dissolution test can be applied to radioiodide sodium iodide capsules as a quality assurance procedure.
Yu
Ming-Der
MD
Department of Nuclear Medicine, Tri-Service General Hospital and National Defense University, Taipei, Taiwan. mdyu@ndmctsgh.edu.tw
Huang
Wen-Sheng
WS
Cherng
Chiou-Chi
CC
Shaw
Stanley M
SM
D000328:Adult; D000368:Aged; D001682:Biological Availability; D002626:Chemistry, Pharmaceutical; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007457:Iodine Radioisotopes / Q000493:pharmacokinetics*; D008297:Male; D008875:Middle Aged; D011877:Radionuclide Imaging; D012974:Sodium Iodide / Q000493:pharmacokinetics*; D013959:Thyroid Diseases / Q000000981:diagnostic imaging; D013961:Thyroid Gland / Q000000981:diagnostic imaging* / Q000378:metabolism; D013997:Time Factors
D007457:Iodine Radioisotopes; D012974:Sodium Iodide