Clinical causes of decreased D1 activity

Condition or drugComment
Low caloric intake, malnutritionThe most common inhibitory factor of type 1 iodothyronine deiodinase (D1)
Nonthyroid illnessEven if it is mild
 PropylthiouracilNot methimazole
 GlucocorticoidsEg, 4 mg of dexamethasone decreases total T3 by 30% in several days
 Beta-adrenergic antagonistsPropranolol, metoprolol, atenolol, and alprenolol (not nadolol or sotalol)
 Oral cholecystographic agents (eg, sodium ipodate)Not available in United States
 AmiodaroneCould compete with thyroxine (T4) for the deiodinative site
Liver diseaseLiver tissue expresses high levels of D1
Selenium deficiencyD1 is a selenoprotein
Neonatal periodEspecially in premature and low-birth-weight infants