Dosing & Uses
Dosage Forms & Strengths
tablet
- 25mcg, 50mcg, 75mcg, 88mcg, 100mcg, 112mcg
- 125mcg, 137mcg, 150mcg, 175mcg, 200mcg, 300mcg
capsule (Tirosint)
- 13mcg, 25mcg, 50mcg, 75mcg, 88mcg
- 100mcg, 112 mcg, 125mcg, 137 mcg, 150mcg
oral solution (Tirosint-SOL)
- 13mcg/mL, 25mcg/mL, 50mcg/mL, 75mcg/mL, 88mcg/mL
- 100mcg/mL, 112mcg/mL, 125mcg/mL, 137mcg/mL, 150mcg/mL
- 175mcg/mL, 200mcg/mL
powder for injection
- 100mcg/vial
- 200mcg/vial
- 500mcg/vial
Mild Hypothyroidism
1.7 mcg/kg or 100-125 mcg PO qDay; not to exceed 300 mcg/day
>50 years (or <50 yr with CV disease)
- Usual initial dose: 25-50 mcg/day
- May adjust dose by 12.5-25 mcg q6-8Week
>50 years with CV disease
- Usual initial dose: 12.5-25 mcg PO qDay
- May adjust dose by 12.5-25 mcg q4-6weeks until patient becomes euthyroid and serum TSH concentration normalized; adjustments q6-8weeks also used
- Dose range: 100-125 mcg PO qDay
Severe Hypothyroidism
Initial: 12.5-25 mcg PO qDay
Adjust dose by 25 mcg/day q2-4Week PRN
Subclinical Hypothyroidism
Initial: 1 mcg/kg PO qDay may be adequate, OR
If replacement therapy not initiated, monitor patient annually for clinical status
Myxedema Coma
300-500 mcg IV once, THEN 50-100 mcg qDay until patient is able to tolerate oral administration; may consider smaller doses in patients with cardiovascular disease
Organ Preservation (Orphan)
Preservation of organ function in brain-dead organ donors
Orphan indication sponsor
- Fera Pharmaceuticals, LLC; 134 Birch Hill Road; Locust Valley, NY 11560
Dosing Considerations
Lower dose of Tirosint capsules may be required compared with standard T4 tablets for hypothyroidism in patients with impaired gastric acid secretion to reach their target TSH levels; Tirosint has shown improved absorption compared with conventional T4 tablets
Check for bioequivalence if switching brands/generics, OR every week after switching from one levothyroxine sodium preparation to another
Monitor serum thyroid levels; patient may be asymptomatic
Monitoring
- Initially evaluate patients q6-8Week
- Once normalization of thyroid function and serum TSH conc achieved, evaluate q6-12mo
Dosage Forms & Strengths
tablet
- 25mcg, 50mcg, 75mcg, 88mcg, 100mcg, 112mcg
- 125mcg, 137mcg, 150mcg, 175mcg, 200mcg, 300mcg
capsule (Tirosint)
- 13mcg, 25mcg, 50mcg, 75mcg, 88mcg
- 100mcg, 112 mcg, 125mcg, 137 mcg, 150mcg
oral solution (Tirosint-SOL)
- 13mcg/mL, 25mcg/mL, 50mcg/mL, 75mcg/mL, 88mcg/mL
- 100mcg/mL, 112mcg/mL, 125mcg/mL, 137mcg/mL, 150mcg/mL
- 175mcg/mL, 200mcg/mL
powder for injection
- 200mcg/vial
- 500mcg/vial
Hypothyroidism
Age 1-3 months
Dosing considerations
- Check for bioequivalence if switching brands/generics
- May minimize hyperactivity in older children by initiating dose at 1/4 of recommended dose; increase by that amount each week until full dose achieved
- Start children with severe or chronic hypothyroidism at 25 mcg/day; adjust dose by 25 mcg qweek
Because of increased prevalence of cardiovascular disease among the elderly, initiate therapy at less than full replacement dose; atrial arrhythmias can occur in elderly patients; atrial fibrillation is the most common of arrhythmias observed with levothyroxine overtreatment in the elderly
Interactions
Interaction Checker
No Results
Contraindicated
Serious - Use Alternative
Significant - Monitor Closely
Minor
Adverse Effects
Frequency Not Defined
Angina pectoris
Arthralgia
Congestive heart failure
Flushing
Increased pulse
Myocardial infarction
Palpitations
Arrhythmias
Cramps
Diarrhea
Nervousness
Anxiety
Choking sensation
Emotional lability
Headache
Heat intolerance
Insomnia
Myasthenia
Pseudomotor cerebri
Alopecia
Weight loss
Infertility
Dyspnea
Fever
Tachycardia
Tremor
Decreased bone mineral density
Postmarketing Reports
Musculoskeletal: Muscle weakness, muscle spasm
Dermatologic: Hair loss, rash
Slipped capital femoral epiphysis (children)
Warnings
Black Box Warnings
Thyroid hormones, either alone or with other therapeutic agents, should not be used for the treatment of obesity or for weight loss
In euthyroid patients, doses within the range of daily hormonal requirements are ineffective for weight reduction; larger doses may produce serious or even life-threatening manifestations of toxicity, particularly when given in association with sympathomimetic amines such as those used for their anorectic effects
Contraindications
Hypersensitivity to thyroid hormone or other ingredients
Acute MI, thyrotoxicosis, uncorrected adrenal insufficiency
Treatment of obesity or infertility
No contraindications reported by manufacturer for myxedema coma when treated with injection
Cautions
Avoid undertreatment or overtreatment, which may result in adverse effects
Proper dose titration and careful monitoring is critical to prevent persistence of hypothyroidism or development of hyperthyroidism
Use caution in cardiovascular disease, HTN, endocrine disorders, osteoporosis, or myxedema
Over-treatment with levothyroxine may cause increase in heart rate, cardiac wall thickness, and cardiac contractility; may precipitate angina or arrhythmias, particularly in patients with cardiovascular disease and in elderly patients; monitor patients receiving concomitant levothyroxine and sympathomimetic agents for signs and symptoms of coronary insufficiency; initiate lower dose in elderly, those with angina pectoris, cardiovascular disease, or in those with severe hypothyroidism
Over- or under-treatment with levothyroxine may have negative effects on growth and development, cardiovascular function, bone metabolism, reproductive function, cognitive function, emotional state, gastrointestinal function, and on glucose and lipid metabolism; titrate dose carefully and monitor response to titration to avoid these effects
Monitor for presence of drug or food interactions when using levothyroxine and adjust dose as necessary; symptoms may be exacerbated or aggravated in patients with diabetes mellitus and insipidus; addition of levothyroxine therapy in patients with diabetes mellitus may worsen glycemic control and result in increased antidiabetic agent or insulin requirements
Use of oral thyroid hormone drug products is not recommended to treat myxedema coma; administer thyroid hormone products formulated for intravenous administration to treat myxedema coma; myxedema coma is a life-threatening emergency characterized by poor circulation and hypometabolism, and may result in unpredictable absorption of levothyroxine sodium from the gastrointestinal tract
Do NOT generally use levothyroxine sodium preparations interchangeably, due to narrow therapeutic index
Check for bioequivalence if switching brands/generics
Synthroid and unithroid tabs contain lactose
Not recommended for TSH suppression in patients with thyroid nodules
Levoxyl tabs swell in mouth: take with full glass of water to avoid choking
Avoid use in postmenopausal women >60 years with osteoporosis, cardiovascular disease, or systemic illness
Avoid use in patients with large thyroid nodules or long-standing goiters, or low-normal TSH levels
Long-term therapy decreases bone mineral density; use lowest dose in postmenopausal women and women using suppressive doses
Use caution in patients with adrenal insufficiency; may exacerbate symptoms or agravate them; treatment with glucocorticoids should precede levothyroxine therapy adrenal insufficiency present; initiation of thyroid hormone therapy prior to initiating glucocorticoid therapy may precipitate acute adrenal crisis in patients with adrenal insufficiency
Monitor for presence of drug or food interactions when using levothyroxine and adjust dose as necessary
Pregnancy & Lactation
Pregnancy
Experience with levothyroxine use in pregnant women, including data from post-marketing studies, have not reported increased rates of major birth defects or miscarriages; there are risks to mother and fetus associated with untreated hypothyroidism in pregnancy; since TSH levels may increase during pregnancy, TSH should be monitored and levothyroxine dosage adjusted during pregnancy; untreated maternal hypothyroidism may have adverse effect on fetal neurocognitive development
Maternal hypothyroidism during pregnancy is associated with a higher rate of complications, including spontaneous abortion, gestational hypertension, pre-eclampsia, stillbirth, and premature delivery; untreated maternal hypothyroidism may have adverse effect on fetal neurocognitive development
Pregnancy may increase thyroid hormone requirements. serum TSH level should be monitored and the dosage adjusted during pregnancy; since postpartum TSH levels are similar to preconception values, the dosage should return to the pre-pregnancy dose immediately after delivery
Lactation
Limited published studies report that levothyroxine is present in human milk; however, there is insufficient information to determine effects of levothyroxine on breastfed infant and no available information on effects of levothyroxine on milk production; adequate levothyroxine treatment during lactation may normalize milk production in hypothyroid lactating mothers; developmental and health benefits of breastfeeding should be considered along with mother’s clinical need for levothyroxine and any potential adverse effects on breastfed infant from levothyroxine or from underlying maternal condition
Pregnancy Categories
A:Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.
B:May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.
C:Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.
D:Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.
X:Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.
NA:Information not available.
Pharmacology
Mechanism of Action
Synthetic T4; thyroid hormone increases basal metabolic rate, increases utilization and mobilization of glycogen stores, promotes gluconeogenesis; involved in growth development and stimulates protein synthesis
Absorption
40-80% from GI tract (PO)
Bioavailability: 64% (nonfasting); 79-81% (fasting)
Peak plasma time: 2-4 hr (PO)
Duration: Hypothyroidism, several weeks
Onset, hypothyroidism
- Initial response: 3-5 days (PO); 6-8 hr (IV)
- Maximum effect: Several weeks
- Peak effect: 24 hr (IV)
Onset, myxedema coma
- Initial response: 6-12 hr (IV)
- Peak effect: 24 hr
Distribution
Protein bound: 99%
Vd: 9-10 L
Metabolism
Deiodinated in blood and then 50% converted to active metabolite, triiodothyronine (T3), also by liver
Metabolites: T3 (active)
Elimination
Half-life: 9-10 days (hypothyroid); 3-4 days (hyperthyroid); 6-7 days (euthyroid)
Total body clearance: 0.8-1.4 L/day
Excretion: Urine (major), feces (20%)
Administration
IV Preparation
Add 5 mL of NS to vial containing 200 or 500 mcg and shake until a clear solution is obtained; resultant solutions contain approximately 40 or 100 mcg/mL, respectively
Use reconstituted solutions immediately; discard any unused portions
Alternatively, add 2 mL NS to vial containing 200 mcg to produce Synthroid solution containing approximately 100 mcg/mL
Do not admix with IV infusion solutions
Oral Administration
Take tabs with full glass of water preferably 30 min to 1 hr before breakfast on empty stomach
Do not use foods that decrease absorption (soybean products) for administering levothyroxine
Administer oral levothyroxine >4 hr apart from drugs known to interfere with absorption
IV/IM: Administer 50% of PO dose
Patients unable to swallow intact tabs
- Crush appropriate dose and place in 5-10 mL of water
- Administer resultant suspension by spoon or dropper immediately, do NOT store
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Patient Handout
Formulary
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