title: Single-dose T3 administration: kinetics and effects on biochemical and physiological parameters.
abstract: BACKGROUND
  As changes in thyroid stimulating hormone (TSH), thyroid hormones, and vital signs after administration of a single dose of liothyronine have typically only been documented for 24 hours, we documented these parameters more than 96 hours.
  
  
  METHODS
  Blood samples were obtained for 4 days after administration of 50-mcg liothyronine to 12 healthy euthyroid participants. Concentrations of total and free triiodothyronine, free and total thyroxine, and TSH were measured. Vital signs were documented.
  
  
  RESULTS
  Triiodothyronine concentrations peaked at 2.5 hours after liothyronine administration. Heart rate (HR) increased by 5 hours after liothyronine administration, subsequently reaching a value higher than baseline (P = 0.009). Suppression of TSH concentrations began at 2 hours. The nadir TSH value at 12 hours was significantly different from baseline (P < 0.001) and remained lower than the baseline value for 2-3 days.
  
  
  CONCLUSIONS
  A single dose of liothyronine has both short-term and long-term effects. There is clearly a different lag time between the serum concentrations of triiodothyronine and its effects on the heart and pituitary, respectively. The increase in serum triiodothyronine concentration occurred within hours and was then followed by an increase in HR. The increased HR was transient and was followed by a reduction in TSH concentration. The suppression of TSH was delayed but was more sustained. Thus, sustained TSH reduction beyond 24 hours was achieved by a single dose of liothyronine that produced only brief increases in serum triiodothyronine levels and transient increases in HR.
authors: *Division of Endocrinology, Georgetown University Medical Center; †Endocrine Section, Washington Hospital Center, Washington, DC; ‡Department of Biostatistics, Medstar Health Research Institute, Hyattsville, MD; and §IPE Inc, Kingsport, TN.
authors: Jacqueline
authors: J
authors: Jonklaas
authors: Kenneth D
authors: KD
authors: Burman
authors: Hong
authors: H
authors: Wang
authors: Keith R
authors: KR
authors: Latham
mesh_terms: D000293:Adolescent; D000328:Adult; D001831:Body Temperature / Q000187:drug effects; D001835:Body Weight / Q000187:drug effects; D005260:Female; D006207:Half-Life; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D008297:Male; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000493:pharmacokinetics* / Q000494:pharmacology*; D055815:Young Adult
chemical_list: D014284:Triiodothyronine; D013972:Thyrotropin; D013974:Thyroxine