DOSAGE AND ADMINISTRATION
The dosage of Thyrolar Tablets (Liotrix Tablets, USP) is determined by the indication and must in every case be individualized according to patient response and laboratory findings.
Thyroid hormones are given orally. In acute, emergency conditions, injectable sodium levothyroxine may be given intravenously when oral administration is not feasible or desirable, as in the treatment of myxedema coma, or during total parenteral nutrition. Intramuscular administration is not advisable because of reported poor absorption.
Therapy is usually instituted using low doses with increments which depend
on the cardiovascular status of the patient. The usual starting dose is one
tablet of Thyrolar (liotrix) ½ with increments of one tablet of Thyrolar (liotrix) !4 every
2 to 3 weeks. A lower starting dosage, one tablet of Thyrolar (liotrix) %/day, is recommended
in patients with long-standing myxedema, particularly if cardiovascular impairment
is suspected, in which case extreme caution is recommended. The appearance of
angina is an indication for a reduction in dosage. Most patients require one
tablet of Thyrolar (liotrix) 1 to one tablet of Thyrolar (liotrix) 2 per day. Failure to respond
to doses of one tablet of Thyrolar (liotrix) 3 suggests lack of compliance or malabsorption.
Maintenance dosages of one tablet of Thyrolar (liotrix) 1 to one tablet of Thyrolar (liotrix) 2
per day usually result in normal serum levothyroxine (T4) and triiodothyronine
(T3) levels. Adequate therapy usually results in normal TSH and T4 levels after
2 to 3 weeks of therapy.
Readjustment of thyroid hormone dosage should be made within the first four weeks of therapy, after proper clinical and laboratory evaluations, including serum levels of T4, bound and free, and TSH.
T3 may be used in preference to levothyroxine (T4) during radio-isotope scanning
procedures, since induction of hypothyroidism in those cases is more abrupt
and can be of shorter duration. It may also be preferred when impairment of
peripheral conversion of T4 and T3 is suspected.
Myxedema coma is usually precipitated in the hypothyroid patient of long-standing
by intercurrent illness or drugs such as sedatives and anesthetics and should
be considered a medical emergency. Therapy should be directed at the correction
of electrolyte disturbances and possible infection besides the administration
of thyroid hormones. Corticosteroids should be administered routinely. T4 and
T3 may be administered via a nasogastric tube but the preferred route of administration
of both hormones is intravenous. Sodium levothyroxine (T4) is given at a starting
dose of 400 mcg (100 mcg/mL) given rapidly, and is usually well tolerated, even
in the elderly. This initial dose is followed by daily supplements of 100 to
200 mcg given IV. Normal T4 levels are achieved in 24 hours followed in 3 days
by threefold elevation of T3. Oral therapy with thyroid hormone would be resumed
as soon as the clinical situation has been stabilized and the patient is able
to take oral medication.
Exogenous thyroid hormone may produce regression of metastases from follicular
and papillary carcinoma of the thyroid and is used as ancillary therapy of these
conditions with radioactive iodine. TSH should be suppressed to low or undetectable
levels. Therefore, larger amounts of thyroid hormone than those used for replacement
therapy are required. Medullary carcinoma of the thyroid is usually unresponsive
to this therapy.
Thyroid Suppression Therapy
Administration of thyroid hormone in doses higher than those produced physiologically
by the gland results in suppression of the production of endogenous hormone.
This is the basis for the thyroid suppression test and is used as an aid in
the diagnosis of patients with signs of mild hyperthyroidism in whom baseline
laboratory tests appear normal, or to demonstrate thyroid gland autonomy in
patients with Grave's ophthalmopathy. 131I uptake is determined before and after
the administration of the exogenous hormone. A fifty percent or greater suppression
of uptake indicates a normal thyroid-pituitary axis and thus rules out thyroid
For adults, the usual suppressive dose of levothyroxine (T4) is 1.56 mcg/kg of body weight per day given for 7 to 10 days. These doses usually yield normal serum T4 and T3 levels and lack of response to TSH.
Thyroid hormones should be administered cautiously to patients in whom there is strong suspicion of thyroid gland autonomy, in view of the fact that the exogenous hormone effects will be additive to the endogenous source.
Pediatric dosage should follow the recommendations summarized in Table 1. In
infants with congenital hypothyroidism, therapy with full doses should be instituted
as soon as the diagnosis has been made.
Recommended Pediatric Dosage for Congenital Hypothyroidism
|| Dose per day in mcg
|| T3/T4 to T3/T4
| 0-6 mos
|| 3.1/12.5 to 6.25/25
| 6-12 MOs
|| 6.25/25 to 9.35/37.5
| 1-5 yrs
|| 9.35/37.5 to 12.5/50
| 6-12 yrs
|| 12.5/50 to 18.75/75
| Over 12 yrs
|| over 18.75/75
Thyrolar Tablets (Liotrix Tablets, USP) are available in five potencies coded as follows:
(T3/T4 per tablet)
|| 3.1 mcg/ 12.5 mcg
|| 6.25 mcg/ 25 mcg
|| 12.5 mcg/ 50 mcg
|| 25 mcg/ 100 mcg
|| 37.5 mcg/ 150 mcg
Supplied in bottles of 100, two-layered compressed tablets.
Tablets should be stored at cold temperature, between 36F and 46F (2C and
8C) in a tight, light-resistant container.
Note: (T3 liothyronine sodium is approximately four times as potent as T4 thyroxine on a microgram for microgram basis.)
Forest Pharmaceuticals, Inc. A Subsidiary of Forest Laboratories, Inc. St.
Louis, MO 63045. Rev. 04/05