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Thyrel TRH (protirelin) is indicated as an adjunctive agent in the diagnostic assessment of thyroid function. As an adjunct to other diagnostic procedures, testing with Thyrel® TRH (protirelin) may yield useful information in patients with pituitary or hypothalamic dysfunction.
Thyrel TRH (protirelin) is indicated as an adjunct to evaluate the effectiveness of thyrotropin suppression with a particular dose of T4 in patients with nodular or diffuse goiter. A normal TSH baseline value and a minimal difference between the 30 minute and baseline response to Thyrel TRH (protirelin) injection would indicate adequate suppression of the pituitary secretion of TSH.
Thyrel TRH (protirelin) may be used, adjunctively, for adjustment of thyroid hormone dosage given to patients with primary hypothyroidism. A normal or slightly blunted TSH response, thirty minutes following Thyrel TRH (protirelin) injection, would indicate adequate replacement therapy.
DOSAGE AND ADMINISTRATION
Thyrel TRH (protirelin) is intended for intravenous administration with the patient in the supine position. The drug is administered as a bolus over a period of 15 to 30 seconds, with the patient remaining supine until all scheduled postinjection blood samples have been taken. Blood pressure should be measured before Thyrel TRH (protirelin) is administered and at frequent intervals during the first 15 minutes thereafter (see WARNINGS). Have the patient urinate before injecting Thyrel TRH (protirelin) .
Adults: 500 µg. Doses between 200 and 500 µg have been used. 500 µg is considered the optimum dose to give the maximum response in the greatest number of patients. Doses greater than 500 µg are unlikely to elicit a greater TSH response.
Children age 6 to 16 years; 7 µg/kg body weight up to dose of 500 µg.
Infants and children up to 6 years: Experience is limited in this age group; doses of 7 µg/kg have been administered.
One blood sample for TSH assay should be drawn immediately prior to the injection of Thyrel® TRH, and a second sample should be obtained 30 minutes after injection.
The TSH response to Thyrel TRH (protirelin) is reduced by repetitive administration of the drug. Accordingly, if the Thyrel TRH (protirelin) test is repeated, an interval of seven days before testing is recommended.
INTERPRETATION OF TEST RESULTS
Interpretation of the TSH response to Thyrel TRH (protirelin) requires an understanding of thyroid-pituitary-hypothalamic physiology and knowledge of the clinical status of the individual patient.
Because the TSH test results may vary with the laboratory, the physician should be familiar with the TSH assay method used and the normal range for the laboratory performing the assay. TSH response 30 minutes after Thyrel TRH (protirelin) administration in normal subjects and in patients with hyperthyroidism and hypothyroidism are presented in Figure 1. The diagnoses were established prior to the administration of Thyrel TRH (protirelin) on the basis of the clinical history, physical examination, and the results of other thyroid and/or pituitary function tests.
Among the normal euthyroid subjects, women and children were found to have higher levels of TSH at 30 minutes than men.
Among the patients with hyperthyroidism or primary (thyroidal), secondary pituitary), or tertiary (hypothalamic) hypothyroidism, no significant differences in TSH levels by age or sex were found.
Normal: Baseline TSH levels of less than 10 microunits/mL (µU/mL) were observed in 97% of euthyroid normal subjects tested. Thirty minutes after Thyrel TRH (protirelin) , the serum TSH increased by 2.0 mµ/mL or more in 95% of euthyroid subjects.
Hyperthyroidism: All hyperthyroid patients tested had baseline TSH levels of less than 10 µU/mL and a rise of less than 2 µU/mL 30 minutes after Thyrel® TRH.
Primary (thyroidal) hypothyroidism: The diagnosis of primary hypothyroidism is frequently supported by finding clearly elevated baseline TSH levels; 93% of patients tested had levels above 10 µU/mL, Thyrel TRH (protirelin) administration to these patients generally would not be expected to yield additional useful information. Ninety-four percent of patients with primary hypothyroidism given Thyrel® TRH in clinical trials responded with a rise in TSH of 2.0 µU/mL or greater. Since this response is also found in normal subjects, Thyrel TRH (protirelin) testing does not differentiate primary hypothyroidism from normal.
|Change of |
at 30 minutes
(normal thyroid function)
|10 or less |
(usually 6 or less; 20% have
|2 or more |
(usually 6 to 30)
|Hyperthyroidism||10 or less |
(usually 4 or less)
|less than 2|
|more than 10 |
(usually 15 to 100)
|2 or more |
(usually 20 or
|10 or less |
(usually 6 or less)
|less than 2 (59%) |
2 to 50 (41%)
|10 or less |
(often less than 2)
|2 or more|
Secondary (pituitary) and tertiary (hypothalamic) hypothyroidism: In the presence of clinical and other laboratory evidence of hypothyroidism, the finding of a baseline TSH level less than 10 µU/mL should suggest secondary or tertiary hypothyroidism. In this situation, a response to Thyrel TRH (protirelin) of less than 2 µU/mL suggests secondary hypothyroidism since this response was observed in about 60% of patients with secondary hypothyroidism and only approximately 5% of patients with tertiary hypothyroidism. A TSH response to Thyrel TRH (protirelin) greater than 2 µU/mL is not helpful in differentiating between secondary and tertiary hypothyroidism since this response was noted in about 40% of the former and about 95% of the latter.
Establishing the diagnosis of secondary or tertiary hypothyroidism requires a careful history and physical examination along with appropriate tests of anterior pituitary and/or target gland function. The Thyrel TRH (protirelin) test should not be used as the only laboratory determinant for establishing these diagnoses.
As 1 mL ampuls boxes of 5 (NDC 55566-0081-5). Each mL contains Thyrel TRH (protirelin) 0.50 mg (500 µg), sodium chloride 9.0 mg for isotonicity, hydrochloric acid and sodium hydroxide as needed to adjust pH.
Store at controlled room temperature 15° to 30°C (59° to 86°F).
FERRING PHARMACEUTICALS INC.
Tarrytown, NY 10591
By: Taylor Pharmaceuticals
Decatur, IL 6252
Last reviewed on RxList: 1/18/2005
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