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Levothyroxine Nursing Considerations & Implications | Bioavailable

Compound database
Thyroid hormones
Levothyroxine

LevothyroxineNursing considerations

Known brand names include Synthroid, Levoxyl, Unithroid, Euthyrox, and Tirosint.

Synthetic thyroid hormone (T4), taken once a day on an empty stomach to replace what an underactive thyroid no longer makes. It is usually taken for life.

Nursing implications

Hold parameters

Reduce or pause the dose if signs of overdose (hyperthyroidism) appear
Do not start until adrenal insufficiency is corrected with glucocorticoids
Do not use the oral form to treat myxedema coma

Sources: [1][2][3]

Administration

Once daily on an empty stomach, a half hour to 1 hour before breakfast
Take at least 4 hours apart from calcium, iron, antacids, and other binding drugs
Children who cannot swallow tablets: crush and mix in 5 to 10 mL of water, give immediately by spoon or dropper, and never store the mixture
Avoid giving with soybean-based infant formula

Sources: [1]

Assess and report

Side effects by what to assess

General

Hyperthyroid symptoms from overdose: heat intolerance, sweating, weight loss, tremor, insomnia, anxiety, diarrhea

Vital signs

Palpitations and tachycardia
Atrial fibrillation, angina, MI, or heart failure with overtreatment, especially in older or cardiac patients (serious)
Acute adrenal crisis if adrenal insufficiency is untreated (serious)

Musculoskeletal

Loss of bone density from over-replacement (serious)

Glucose

Worse glucose control in diabetes (serious)

Sources: [1][2][3][4][5]

Labs and vitals

Blood glucose

Why: Worsened diabetes control
When: When thyroid therapy is started, changed, or stopped
Normal: Fasting 70 to 99 mg/dL.

Sources: [1][2]

Heart rate

Why: Overtreatment, tachycardia, atrial fibrillation
When: During titration, especially in older and cardiac patients
Act on: Reduce or pause the dose for signs of overdose
Normal: 60 to 100 beats per minute in adults at rest.

Sources: [1][2][3]

INR (prothrombin time)

Why: Stronger warfarin effect
When: Closely when correcting hypothyroidism or raising the dose in patients on warfarin
Act on: The warfarin dose may need to drop
Normal: INR 0.8 to 1.1 when not on a blood thinner. On warfarin, the usual target is 2.0 to 3.0.

Sources: [1][2]

TSH (thyroid-stimulating hormone)

Why: Dose adequacy in primary hypothyroidism
When: 6 to 8 weeks after any dose change; every 6 to 12 months when stable. Stop biotin 2 days before
Act on: Titrate by 12.5 to 25 mcg until TSH normalizes
Normal: 0.4 to 4.8 µU/mL.

Sources: [1][2][3]

Safety

High-alert status

Oral levothyroxine is not on the ISMP acute care high-alert list.

Sources: [1]

Narrow therapeutic index

Narrow therapeutic index. The label states that levothyroxine has a narrow therapeutic index, so doses are titrated against TSH.

Sources: [1]

Boxed warning

Not for obesity or weight loss. Replacement doses do not reduce weight in people with normal thyroid function, and larger doses can cause serious or life-threatening toxicity, especially with sympathomimetic appetite suppressants.

Sources: [1]

Antidote or reversal

No antidote. Overdose looks like hyperthyroidism, sometimes with confusion, and can be delayed for days. Reduce or pause the dose and give supportive care.

Sources: [1]

Patient teaching

This replaces a hormone the thyroid should make; treatment is usually lifelong
Symptoms may take several weeks to improve
Take it alone on an empty stomach, and keep iron, calcium, and antacids at least 4 hours away
Do not use it for weight loss
Stop biotin supplements at least 2 days before thyroid blood tests
Tell the prescriber about pregnancy, heart disease, diabetes, or clotting disorders

Sources: [1]

Sound-alike and look-alike names

levothyroxine and lamoTRIgine
levothyroxine and Lanoxin
levothyroxine and liothyronine

Sources: [1]

Dosing

Doses come from the FDA label. Study tool, not for clinical decisions.

Adult dose

Hypothyroidism: Full replacement is about 1.6 mcg/kg/day. Titrate by 12.5 to 25 mcg every 4 to 6 weeks to euthyroid. More than 200 mcg/day is seldom needed; poor response above 300 mcg/day suggests poor adherence, malabsorption, or interactions.
Older adults or cardiac disease: Start below 1.6 mcg/kg/day and titrate every 6 to 8 weeks.

Sources: [1]

Renal adjustment

The label gives no renal dose adjustment. Dosing is based on age, weight, cardiac status, and TSH or free T4.

Sources: [1][2]

Hepatic adjustment

The label gives no hepatic dose adjustment. Dosing is based on age, weight, cardiac status, and TSH or free T4.

Sources: [1][2]

How it works

Mechanism

Synthetic T4. Tissues convert it to T3, which supplies about 80% of active thyroid hormone. T3 binds nuclear thyroid receptors and switches on gene transcription and protein synthesis. Full effect of a dose change takes 4 to 6 weeks.

Sources: [1][2]