LEVOTHYROXINE SODIUM
(Eltroxin, Synthroid, Thyroxine, T4)Standard Prescription
levothyroxin__mcg PO once daily (__mcg/kg/24hr)
Dosages
PO (full replacement doses):
0-3 mos.: 10-15 mcg/kg PO once daily
3-6 mos.: 8-10 mcg/kg PO once daily
6-12 mos.: 6-8 mcg/kg PO once daily.
1-5 yrs: 5-6 mcg/kg PO once daily
5-12 yrs: 4-5 mcg/kg PO once daily
12 yrs to adult: 2-3 mcg/kg PO once daily (average adult dose is 1.6 mcg/kg/24 hr)
IV:
Infants and Children: 50-75% of oral doses recommended above.
IV dose should be reviewed with an endocrinologist if switching from PO to IV.
0-3 mos.: 10-15 mcg/kg PO once daily
3-6 mos.: 8-10 mcg/kg PO once daily
6-12 mos.: 6-8 mcg/kg PO once daily.
1-5 yrs: 5-6 mcg/kg PO once daily
5-12 yrs: 4-5 mcg/kg PO once daily
12 yrs to adult: 2-3 mcg/kg PO once daily (average adult dose is 1.6 mcg/kg/24 hr)
IV:
Infants and Children: 50-75% of oral doses recommended above.
IV dose should be reviewed with an endocrinologist if switching from PO to IV.
Mechanism of Action
Synthetic thyroxine (T4)
Forms Supplied
tablet: 25 mcg, 50 mcg, 75 mcg, 88 mcg, 100 mcg, 112 mcg, 125 mcg, 150 mcg, 200 mcg
(also available but not stocked at BCCH: 137 mcg, 175 mcg, 300 mcg tablets)
injection: 500 mcg/vial
(also available but not stocked at BCCH: 137 mcg, 175 mcg, 300 mcg tablets)
injection: 500 mcg/vial
Comments
Titrate doses at 2 to 4-week intervals initially, to obtain a mid-normal TSH level for primary hypothyroidism or free T4 level in the upper half of the normal range for secondary hypothyroidism, as well as a clinically euthyroid state. Thereafter, check levels every 3-6 months.
Doses between available tablet sizes can be achieved by using 1/2 of a larger tablet (e.g. 1/2 of a 75-mcg tablet to give 37.5 mcg).
Different brands can be interchanged as per the College of Pharmacists of BC's 2004 policy. However, if a patient has been on levothyroxine previously, it is preferable to continue the therapy with the same brand. If a different brand is dispensed, suggest monitoring TSH and/or free T4 levels. Very unstable in solution; if oral liquid must be given, administer dose immediately after mixing.
Levothyroxine has a very long half-life (6-7 days); patients on chronic therapy can go without a dose for up to 7 days if they are NPO for any reason.
Doses between available tablet sizes can be achieved by using 1/2 of a larger tablet (e.g. 1/2 of a 75-mcg tablet to give 37.5 mcg).
Different brands can be interchanged as per the College of Pharmacists of BC's 2004 policy. However, if a patient has been on levothyroxine previously, it is preferable to continue the therapy with the same brand. If a different brand is dispensed, suggest monitoring TSH and/or free T4 levels. Very unstable in solution; if oral liquid must be given, administer dose immediately after mixing.
Levothyroxine has a very long half-life (6-7 days); patients on chronic therapy can go without a dose for up to 7 days if they are NPO for any reason.
References
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Last Edited
2022-04-04 19:27:36