Switching from Armor Thyroid to Tirosint: A Practical Approach
Switch to levothyroxine monotherapy (Tirosint) using a conversion ratio of approximately 60-65 mcg of levothyroxine for every 1 grain (60 mg) of Armor Thyroid, administered once daily on an empty stomach, with TSH monitoring at 6-8 weeks. 1, 2
Rationale for the Switch
Levothyroxine (T4) monotherapy is the standard of care for hypothyroidism treatment, as it allows the body's natural conversion mechanisms to produce T3 as needed, avoiding the supraphysiologic T3 peaks that occur with desiccated thyroid products. 3 Armor Thyroid contains a 4.22:1 T4:T3 ratio, which differs significantly from the body's natural 11:1 secretion ratio and can cause transient T3 elevations with associated palpitations and other symptoms. 4, 3
Tirosint offers specific advantages over standard levothyroxine tablets: it is a liquid gel-cap formulation that eliminates common excipients like lactose and gluten, potentially improving absorption in patients with gastrointestinal sensitivities or those taking medications that interfere with levothyroxine absorption. 5
Conversion Protocol
Step 1: Calculate the Equivalent Levothyroxine Dose
- For patients on 1 grain (60 mg) of Armor Thyroid: Start with 60-65 mcg of levothyroxine 5
- For patients on 2 grains (120 mg): Start with 120-130 mcg of levothyroxine 5
- Adjust proportionally for other doses 5
Step 2: Initiate Tirosint with Proper Administration
- Administer once daily on an empty stomach, one-half to one hour before breakfast with a full glass of water 2
- Space at least 4 hours away from iron, calcium supplements, or antacids 2
- For patients <70 years without cardiac disease: Can start at the full calculated replacement dose 1
- For patients >70 years or with cardiac disease/multiple comorbidities: Start at 25-50 mcg/day and titrate gradually to avoid cardiac complications 1, 2
Step 3: Monitor and Adjust
- Recheck TSH and free T4 at 6-8 weeks after the switch 1, 2
- Target TSH range: 0.5-4.5 mIU/L with normal free T4 1
- Adjust dose by 12.5-25 mcg increments based on results 1
- Once stable, monitor TSH every 6-12 months or if symptoms change 1
Critical Safety Considerations Before Switching
Rule Out Adrenal Insufficiency
Before initiating or increasing levothyroxine, always exclude concurrent adrenal insufficiency, as starting thyroid hormone before corticosteroids can precipitate life-threatening adrenal crisis. 6, 2 This is particularly important in patients with:
- Central hypothyroidism or pituitary disease 6
- Autoimmune hypothyroidism (increased risk of concurrent Addison's disease) 6
- History of prolonged glucocorticoid use 6
- Unexplained hypotension, hyponatremia, or hyperpigmentation 6
If adrenal insufficiency is suspected, measure morning cortisol and ACTH before any treatment, and initiate glucocorticoid replacement at least 1 week before starting levothyroxine. 6
Expected Changes After Switching
Based on a retrospective case series of 13 patients switched from NDT to liquid levothyroxine formulation:
- TSH levels typically decrease 5
- Free T3 levels remain stable 5
- Free T4 levels increase significantly 5
- Patients report good tolerability 5
The higher free T4 levels are physiologically appropriate because levothyroxine monotherapy must generate from T4 the 20% of daily T3 production that would otherwise come directly from the thyroid gland itself. 3
Common Pitfalls to Avoid
Overtreatment Risks
Approximately 25% of patients on levothyroxine are unintentionally maintained on doses sufficient to fully suppress TSH, increasing serious complication risks. 1 Overtreatment (TSH <0.1 mIU/L) significantly increases risk for:
- Atrial fibrillation and cardiac arrhythmias, especially in elderly patients 1, 2
- Osteoporosis and fractures, particularly in postmenopausal women 1, 2
- Increased cardiovascular mortality 1
Never allow TSH to fall below 0.1 mIU/L in patients treated for hypothyroidism without thyroid cancer. 1
Timing Errors
- Do not recheck TSH before 6-8 weeks after dose adjustment - levothyroxine requires this interval to reach steady state 1, 2
- Do not treat based on a single elevated TSH value - 30-60% of elevated TSH levels normalize spontaneously on repeat testing 1, 7
Drug Interactions
Certain medications reduce levothyroxine absorption or efficacy: 2, 7
- Iron and calcium supplements (space 4 hours apart) 2
- Proton pump inhibitors and antacids 2
- Enzyme inducers (increase metabolism) 7
Special Populations
Elderly Patients with Cardiac Disease
Start at 25-50 mcg/day and increase by 12.5 mcg increments every 6-8 weeks to avoid unmasking cardiac ischemia or precipitating arrhythmias. 1, 2, 7 Rapid normalization of thyroid hormone can worsen angina or trigger atrial fibrillation in this population. 1
Pregnant Women or Those Planning Pregnancy
Optimize thyroid function before conception, targeting TSH <2.5 mIU/L in the first trimester. 1 Levothyroxine requirements typically increase by 25-50% during pregnancy, necessitating dose adjustment immediately upon pregnancy confirmation and TSH monitoring every 4 weeks until stable. 1
Patients with Malabsorption or Taking Interfering Medications
Tirosint's liquid gel-cap formulation may offer superior absorption compared to standard levothyroxine tablets in patients with gastrointestinal disorders, those on proton pump inhibitors, or those requiring concurrent iron or calcium supplementation. 5
Long-Term Management
Once the patient is stable on Tirosint:
- Monitor TSH annually or sooner if symptoms change 1
- Maintain TSH in the reference range (0.5-4.5 mIU/L) 1
- Ensure adequate calcium (1200 mg/day) and vitamin D (1000 units/day) intake if TSH has been chronically suppressed 1
- Reassess the need for continued therapy if hypothyroidism was potentially transient (e.g., postpartum thyroiditis, medication-induced) 7