Action: Levothyroxine is a synthetic form of thyroxine or T4 which is then converted to T3 in the body
Adverse Drug Reactions
Thyrotoxicosis, Hyperthyroidism (from excessive doses)
Headache, irritability, insomnia
Abdominal cramping, diarrhea
Heat intolerance, diaphoresis
Monitor thyroid function
Monitor for indications of hyperthyroidism (anxiety, tachycardia, palpi- tations, tremors, altered appetite, heat intolerance, fever, diaphoresis, weight loss)
Watch for and report nervousness, rapid heart rate, palpitations, trem- ors, altered appetite, heat intolerance, fever, sweating, weight loss, and chest pain.
Recent myocardial infarction
Cardiovascular disorders (hypertension, angina pectoris, ischemic heart disease)
Give orally to treat hypothyroidism and IV to treat myxedema coma.
Give daily on an empty stomach (at least 30–60 min before breakfast with full glass of water).
Measure baseline vital signs, weight, and height, and monitor periodical- ly thereafter.
Monitor for cardiac excitability (angina, chest pain, palpitations, dys- rhythmias).
Monitor T4 and TSH levels.
Be aware that the various formulations of thyroxine are not inter- changeable; instruct clients to notify the provider if a pharmacy dispens- es a different levothyroxine product.
Expect lifelong replacement therapy.
Cholestyramine (Questran), antacids, iron and calcium supplements, and sucralfate (Carafate) reduce absorption, so clients should not take levothyroxine within 4 hr of these drugs
Food reduces absorption
Many antiseizure and antidepressant drugs, including carbamazepine (Tegretol), phenytoin (Dilantin), phenobarbital, and sertraline (Zoloft), decrease levels.
Anticoagulant effects of warfarin (Coumadin) increase.
Cardiac response to catecholamines (such as epinephrine) increases.