Thyroxine

Class	Thyroid hormone
Chemistry	Iodinated tyrosine derivative
Routes of administration	PO
Absorption	60%-80% oral bioavailability
Solubility	pKa=7.43; very slightly soluble in water
Distribution	VOD = 0.15L/kg; highly protein-bound (to thyroxine-binding globulin)
Metabolism	Metabolised by deiodination, by tissue deiodinases
Elimination	Metabolites are further deiodinated into various inactive iodinated compounds. In overdose, some hepatic metabolism occurs, which results in enterohepatic recirculation
Time course of action	Half-life 6-8 days
Target receptor	Not an active drug, but has some (low) affinity for thyroid hormone receptors, which are mainly nuclear receptors which act as transcription factors
Mechanism of action	Metabolised into T3, which then undergoes endocytosis by a variety of transmembrane transporters, and which binds to nuclear transcription factors to perform a variety of functions. Some actions are probably also performed by cytoplasmic and transmembrane receptors, which mediate more acute effects
Clinical effects	Cardiovascular effects (acts as inodilator) Neurological effects (psychiatric, cognitive, neurodevelopmental) Renal effects (increased renal blood flow and improved renal clearance Hepatic effects (increased rate of protein synthesis, increased hepatic metabolism of substances) Gastrointestinal effects (increased gastrointestinal motility, increased appetite) Metabolic effects (increased skeletal muscle protein synthesis, blood flow, contractility, xoygen consumption) Increased shivering and nonshivering thermogenesis
Literature reference	Colucci et al, 2013
CICM details of understanding	Level 3
Mentioned around Deranged Physiology
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