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levothyroxine (Rx)Brand and Other Names:Synthroid, Levoxyl, more...L Thyroxine, Levo T, Levothroid, Levothyroxine T4, Levoxine, Tirosint, Unithroid

 
 
 

Dosing & Uses

AdultPediatric

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

powder for injection

  • 100mcg/vial
  • 200mcg/vial
  • 500mcg/vial
more...

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

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 50% of PO

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

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

powder for injection

  • 200mcg/vial
  • 500mcg/vial
more...

Hypothyroidism

Age 1-3 months

  • 10-15 mcg/kg/day PO 
  • 5-7.5 mcg/kg/day IV/IM
  • Use lower starting dose (25 mcg/day) if patient at risk of cardiac failure; if initial serum T4 lower than 5 mcg/dL begin treatment at higher dose (50 mcg/day)

Age 3-6 months

  • 8-10 mcg/kg/day PO, OR 
  • 25-50 mcg/day PO
  • 4-7.5 mcg/kg/day IV/IM

Age 6-12 months

  • 6-8 mcg/kg/day PO, OR 
  • 50-75 mcg/day PO
  • 3-6 mcg/kg/day IV/IM

Age 1-5 years

  • 5-6 mcg/kg/day PO, OR 
  • 75-100 mcg/day PO
  • 2.5-4.5 mcg/kg/day IV/IM

Age 6-12 years

  • 4-5 mcg/kg/day PO, OR 
  • 100-125 mcg/day PO
  • 2-3.75 mcg/kg/day IV/IM

>12 years

  • 2-3 mcg/kg/day PO, OR 
  • 150 mcg/day PO
  • 1-2.25 mcg/kg/day IV/IM

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

Administration

Take tabs with full glass of water before breakfast on empty stomach

Do not use foods that decrease absorption (soybean infant formula) for administering levothyroxine

Administer oral levothyroxine >4 hr apart from drugs known to interfere with absorption

IV/IM 50-75% of PO

Patients unable to swallow intact tabs/caps

  • Tablets: Crush appropriate dose and place in 5-10 mL of water; administer resultant suspension by spoon or dropper immediately, do NOT store
  • Capsules: Do not administer capsule to children unable to swallow capsule whole
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Interactions

Interaction Checker

levothyroxine and

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     activity indicator 
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    Interactions Found

    Contraindicated

      Serious - Use Alternative

        Significant - Monitor Closely

          Minor

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            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

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            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, untreated 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

            Use caution in cardiovascular disease, HTN, endocrine disorders, osteoporosis, or myxedema

            Initiate lower dose in elderly, those with angina pectoris, cardiovascular disease, or in those with severe hypothyroidism

            Symptoms may be exacerbated or aggravated in patients with diabetes mellitus and insipidus

            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 whould precede levothyroxine therapy adrenal insufficiency present

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            Pregnancy & Lactation

            Pregnancy category: A

            Lactation: Enters breast milk; use caution

            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.

            more...
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            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%)

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            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

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            Images

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            Formulary

            FormularyPatient Discounts

            To view formulary information first create a list of plans. Your list will be saved and can be edited at any time.

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            • View the formulary and any restrictions for each plan.
            • Manage and view all your plans together – even plans in different states.
            • Compare formulary status to other drugs in the same class.
            • Access your plan list on any device – mobile or desktop.

            The above information is provided for general informational and educational purposes only. Individual plans may vary and formulary information changes. Contact the applicable plan provider for the most current information.

            Tier Description
            1 This drug is available at the lowest co-pay. Most commonly, these are generic drugs.
            2 This drug is available at a middle level co-pay. Most commonly, these are "preferred" (on formulary) brand drugs.
            3 This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs.
            4 This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs or specialty prescription products.
            5 This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs or specialty prescription products.
            6 This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs or specialty prescription products.
            NC NOT COVERED – Drugs that are not covered by the plan.
            Code Definition
            PA Prior Authorization
            Drugs that require prior authorization. This restriction requires that specific clinical criteria be met prior to the approval of the prescription.
            QL Quantity Limits
            Drugs that have quantity limits associated with each prescription. This restriction typically limits the quantity of the drug that will be covered.
            ST Step Therapy
            Drugs that have step therapy associated with each prescription. This restriction typically requires that certain criteria be met prior to approval for the prescription.
            OR Other Restrictions
            Drugs that have restrictions other than prior authorization, quantity limits, and step therapy associated with each prescription.
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