Clinical causes of decreased D1 activity
| Condition or drug | Comment |
|---|---|
| Low caloric intake, malnutrition | The most common inhibitory factor of type 1 iodothyronine deiodinase (D1) |
| Nonthyroid illness | Even if it is mild |
| Drugs | |
| Propylthiouracil | Not methimazole |
| Glucocorticoids | Eg, 4 mg of dexamethasone decreases total T3 by 30% in several days |
| Beta-adrenergic antagonists | Propranolol, metoprolol, atenolol, and alprenolol (not nadolol or sotalol) |
| Oral cholecystographic agents (eg, sodium ipodate) | Not available in United States |
| Amiodarone | Could compete with thyroxine (T4) for the deiodinative site |
| Liver disease | Liver tissue expresses high levels of D1 |
| Selenium deficiency | D1 is a selenoprotein |
| Neonatal period | Especially in premature and low-birth-weight infants |