THYREL TRH
Clinical safety rating: caution
Comprehensive clinical and safety monograph for THYREL TRH (THYREL TRH).
Synthetic thyrotropin-releasing hormone (TRH) that stimulates the release of thyroid-stimulating hormone (TSH) and prolactin from the anterior pituitary.
| Metabolism | Rapidly metabolized by plasma and tissue peptidases; half-life approximately 5 minutes. |
| Excretion | Primarily renal excretion of intact TRH and metabolites (deamido-TRH and acid-TRH). Approximately 90% of administered radioactivity is recovered in urine within 24 hours. Biliary/fecal excretion accounts for less than 10%. |
| Half-life | Terminal elimination half-life is approximately 5–6 minutes in healthy adults. This short half-life reflects rapid enzymatic degradation and renal clearance, requiring rapid intravenous administration for diagnostic thyroid stimulation. |
| Protein binding | Minimal protein binding (<10%). Does not significantly bind to albumin or other plasma proteins. |
| Volume of Distribution | Approximately 0.2 L/kg, reflecting distribution primarily into extracellular fluid and rapid tissue uptake. Confined largely to the central compartment. |
| Bioavailability | Intravenous: 100% (standard route). Oral: <5% due to extensive first-pass metabolism and degradation in gastrointestinal tract. Intramuscular: ~80–90%. |
| Onset of Action | Intravenous: TSH peak occurs at 15–30 minutes post-injection; prolactin peak at 10–20 minutes. Intramuscular: Onset slightly delayed, TSH peak at 20–40 minutes. |
| Duration of Action | TSH elevation persists for 2–4 hours, returning to baseline by 4–6 hours. Prolactin elevation lasts 1–2 hours. Clinical effect (thyroid stimulation) lasts up to 24 hours for radioiodine uptake studies. |
Adult: 500 mcg IV bolus over 15-30 seconds; may repeat once after 15-30 minutes if needed.
| Dosage form | INJECTABLE |
| Renal impairment | No specific dose adjustment recommended based on GFR; use with caution in severe renal impairment. |
| Liver impairment | No specific dose adjustment based on Child-Pugh score. |
| Pediatric use | Children: 7 mcg/kg IV bolus (max 500 mcg). |
| Geriatric use | No specific adjustment; monitor for adverse effects due to potential age-related physiological changes. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for THYREL TRH (THYREL TRH).
| Breastfeeding | Excreted in breast milk; M/P ratio unknown. Can stimulate prolactin release, potentially affecting lactation. Use with caution; consider risk-benefit. |
| Teratogenic Risk | No adequate well-controlled studies in pregnant women; animal studies not available. Prolactin-releasing hormone; theoretical risk of placental abruption if inducing uterine contractions. Use only if clearly needed. |
| Fetal Monitoring |
■ FDA Black Box Warning
None
| Serious Effects |
["Hypersensitivity to TRH or any component of the formulation","Pregnancy (Category C; use only if clearly needed)"]
| Precautions | ["Hypotension or hypertension may occur","May cause nausea, flushing, urinary urgency, and dizziness","Caution in patients with cardiovascular disease due to blood pressure changes"] |
Loading safety data…
| Monitor TSH, prolactin, and T4 levels during prolonged therapy. Observe for signs of uterine contraction or bleeding if used in third trimester. |
| Fertility Effects | May increase prolactin levels, potentially causing galactorrhea or amenorrhea; short-term use unlikely to impair fertility, but long-term hyperprolactinemia may reduce fertility. |