OBJECTIVETo study the best observation time for drug administration and withdrawal in the treatment of children with transient congenital hypothyroidism,seeking an objective basis for the safe drug withdrawal.

METHODSLevothyroxine was prescribed for 1 144 children diagnosed with congenital hypothyroidism (CH) and according to the results levothyroxine was adjusted to a maintenance dosage. Examinations were performed periodically including physical and mental development, thyroid ultrasonography,and blood levels of T3, T4, TSH. For the patients with a small maintenance dosage of levothyroxine (15.0 - 16.6 g/d) and all the examinations normal, levothyroxine was withdrawn at 2 - 3 years, and the children were followed up and reexamined after 1 month, 2 months, and 10 months, respectively. Permanent drug withdrawal was determined for children with all the examinations normal. Once abnormal TSH occurred, levothyroxine was prescribed again, and followed up continuously.

RESULTLevothyroxine was withdrawn from 157 children. During the follow up, for 15 children (9.55%) levothyroxine were prescribed continuously, and for 142 children permanent drug withdrawal (confirmed with transient CH) was determined. Abnormal TSH of various degrees was detected in 48 cases: 25.48 % (40/157),4.46 % (7/157), and 0.64 % (1/157) were detected at 1, 2 and 10 months after drug withdrawal, respectively. In 15 children levothyroxine was prescribed again for the remarkably high TSH, and the other 33 with mildly abnormal TSH finished the treatment since TSH normalized during follow-up.

CONCLUSIONAfter 2 - 3 years of regular treatment, levothyroxine can be withdrawn from children with normal T3, T4, TSH, physical and mental development, and thyroid function. The best observation time for drug withdrawal should be 2 - 3 months. If T3, T4 and TSH levels are in the normal range, drug can be withdrawn safely. Once abnormal results were detected during follow-up, levothyroxine should be administrated continuously.