|LEVOTHYROXINE SODIUM (T4)
Eltroxin , Levoxyl, Levolet, Novothyrox, Synthroid, Unithroid
Classifications: hormone; thyroid hormone replacement; Therapeutic: thyroid hormone replacement
Pregnancy Category: A
25 mcg, 50 mcg, 75 mcg, 88 mcg, 100 mcg, 112 mcg, 125 mcg, 137 mcg, 150 mcg, 175 mcg, 200 mcg, 300 mcg tablets; 200 mcg, 500 mcg injection
Synthetically prepared levo-isomer of thyroxine (T4), with similar actions and uses (thyroxine, principal component of thyroid gland secretions, determines normal thyroid
function). Principal effects include diuresis, loss of weight and puffiness, increased sense of well-being and activity tolerance,
and rise of T3 and T4 serum levels toward normal.
By replacing decreased or absent thyroid hormone, it restores metabolic rate of a hypothyroid individual.
Specific replacement therapy for diminished or absent thyroid function resulting from primary or secondary atrophy of gland,
surgery, excessive radiation or antithyroid drugs, congenital defect. Administered orally for hypothyroid state; administered
IV for myxedematous coma or other thyroid dysfunctions demanding rapid replacement, as well as in failure to respond to
Hypersensitivity to levothyroxine; thyrotoxicosis; severe cardiovascular conditions, acute MI; obesity treatment; adrenal
Cardiac disease, angina pectoris, cardiac arrhythmias, hypertension; diabetes mellitus; older adult, impaired kidney function,
pregnancy (category A).
Route & Dosage
Adult: PO 2550 mcg/d, gradually increased by 50100 mcg q14wk to usual dose of 100400 mcg/d IV/IM ? established oral dose (usually 50100 mcg daily)
Child: PO 06 mo, 810 mcg/kg/d or 2550 mcg/d; 612 mo, 68 mcg/kg/d or 5075 mcg/d; 15 y, 56 mcg/kg/d or 75100 mcg/d; 612 y, 45 mcg/kg/d or 100150 mcg/d; >12 y, 23 mcg/kg/d or >150 mcg/d
Adult: IV 200500 mcg day 1, additional 100300 mcg on day 2 if needed
- Give as a single dose, preferably 1 h before or 2 h after breakfast, to prevent insomnia. Give consistently with respect
- Maintenance dosage for older adults may be 25% lower than for heavier and younger adults.
- Store in tight, light-resistant container.
PREPARE: Direct: Reconstitute vial by adding 5 mL of NS for injection to each 100 mcg. Shake well to dissolve. Use immediately.
ADMINISTER: Direct: Give bolus dose over 1 min.
INCOMPATIBILITIES Do not mix with other medications.
- Store dry powder at 15°30° C (59°86° F).
Adverse Effects (≥1%)CNS:
Irritability, nervousness, insomnia,
headache (pseudotumor cerebri in children), tremors, craniosynostosis (excessive doses in children). CV:
Palpitations, tachycardia, arrhythmias, angina pectoris, hypertension. GI:
, change in appetite. Urogenital:
Menstrual irregularities. Body as a Whole:
Weight loss, heat intolerance, sweating, fever, leg cramps, temporary hair loss (children).
InteractionsDrug: Cholestyramine, colestipol
decrease absorption of levothyroxine; epinephrine, norepinephrine
increase risk of cardiac insufficiency; oral anticoagulants
may potentiate hypoprothrombinemia.
Variable and incompletely absorbed from GI tract (5080%). Peak:
34 wk. Duration:
13 wk. Distribution:
Gradually released into tissue
Assessment & Drug Effects
- Monitor pulse before each dose during dose adjustment. If rate is >100, consult physician.
- Monitor for adverse effects during early adjustment. If metabolism increases too rapidly, especially in older adults and
heart disease patients, symptoms of angina or cardiac failure may appear.
- Note: Levothyroxine may aggravate severity of previously obscured symptoms of diabetes mellitus, Addison's disease, or diabetes
insipidus. Therapy for these disorders may require adjustment.
- Lab tests: Baseline and periodic tests of thyroid function. Closely monitor PT/INR and assess for evidence of bleeding if
patient is receiving concurrent anticoagulant therapy. A decrease in anticoagulant dosage may be needed 14 wk after
concurrent levothyroxine is started.
- Monitor bone age, growth, and psychomotor function in children.
- Some children have partial hair loss after a few months; it returns even with continued therapy.
- Synthroid 100 and 300 mcg tablets contain tartrazine, which may cause an allergic-type reaction in certain patients; particularly
those who are hypersensitive to aspirin.
Patient & Family Education
- Thyroid replacement therapy is usually lifelong.
- Learn how to self-monitor pulse rate. Notify physician if rate begins to increase above 100 or if rhythm changes are noted.
- Notify physician immediately of signs of toxicity (e.g., chest pain, palpitations, nervousness).
- Avoid OTC medications unless approved by physician.