Transient changes in blood pressure, either increases or decreases, frequently occur immediately following administration of TRH. Blood pressure should therefore be measured before TRH is administered and at frequent intervals during the first 15 minutes after its administration.
Increases in systolic pressure (usually less than 30 mm Hg) and/or increases in diastolic pressure (usually less than 20 mm Hg) have been observed more frequently than decreases in pressure. These changes have not ordinarily persisted for more than 15 minutes nor have they required therapy. More severe degrees of hypertension or hypotension with or without syncope have been reported in a few patients. To minimize the incidence and/or severity of hypotension, the patient should be supine before, during, and after TRH administration. If a clinically important change in blood pressure occurs, monitoring of blood pressure should be continued until it returns to base-line levels.
TRH should not be administered to patients in whom marked, rapid changes in blood pressure would be dangerous unless the potential benefit clearly outweighs the potential risk
There is currently no manufacturer warning information available for this drug.
TRH is indicated as an adjunctive agent in the diagnostic assessment of thyroid function. As an adjunct to other diagnostic procedures, testing with TRH (protirelin) may yield useful information in patients with pituitary or hypothalamic dysfunction.
TRH 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 TRH injection would indicate adequate suppression of the pituitary secretion of TSH.
TRH 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 TRH injection, would indicate adequate replacement therapy.
Chemically, TRH (protirelin) is identified as 5-oxo-L-prolyl-L-histidyl-L-proline amide. It is a synthetic tripeptide that is believed to be structurally identical to the naturally-occurring thyrotropin-releasing hormone produced by the hypothalamus. The CAS Registry Number is 24305-27-9. The structural formula is:
Figure 1
TRH is supplied as a solution of 1 mL in a 5 mL vial. Each vial contains 500 mcg protirelin, 1.8 mg Methylparaben, 0.2 mg Propylparaben, and 9.0 mg Sodium Chloride. TRH is intended for intravenous administration following dilution with 1 mL sterile water for injection.