Armour Thyroid Dosing
Armour Thyroid (desiccated thyroid extract) should generally be avoided in favor of levothyroxine monotherapy for hypothyroidism treatment, but if used, typical starting doses are 30-60 mg daily (equivalent to approximately 50-100 mcg levothyroxine), titrated based on TSH monitoring every 6-8 weeks. 1, 2, 3
Why Levothyroxine is Preferred Over Desiccated Thyroid
Levothyroxine (synthetic T4) is the standard of care for hypothyroidism treatment, with once-daily dosing, predictable pharmacokinetics, and a long half-life that prevents harm from occasional missed doses 4, 2
Desiccated thyroid extract (DTE) like Armour Thyroid contains both T4 and T3 in a fixed 4:1 ratio, which frequently causes supranormal T3 peaks during the absorption phase, associated with palpitations and potential cardiac complications 4, 3
DTE remains outside formal FDA oversight, with consistency of T4 and T3 content monitored only by manufacturers, raising concerns about standardization and reliability 3, 5
The lack of standardization in T3 content makes DTE potentially dangerous, particularly when combined with other medications or supplements 5
If Desiccated Thyroid Must Be Used
Initial Dosing Strategy
For patients under 70 years without cardiac disease: Start with 30-60 mg daily (approximately equivalent to 50-100 mcg levothyroxine), based on the principle that mean T4 replacement requires 1.6 mcg/kg/day 1, 4
For patients over 70 years or with cardiac disease: Start with lower doses of 15-30 mg daily to avoid precipitating cardiac complications, similar to the 25-50 mcg levothyroxine starting dose recommended for this population 1, 2
Dose Titration Protocol
Monitor TSH and free T4 every 6-8 weeks during dose adjustments, targeting TSH within the normal reference range (0.5-4.5 mIU/L) 6, 1
Increase dosage by small increments (15-30 mg) every 6-8 weeks until euthyroid, avoiding rapid escalation that could cause transient hyperthyroidism 1, 3
The mean daily dose of DTE needed to normalize TSH contains approximately 11 mcg T3, though some patients may require higher doses 3
Monitoring Requirements
Check TSH monthly initially when using DTE or other agents that can affect thyroid function, as T3-containing preparations can cause more variable hormone levels 7
Once stable, repeat testing every 6-12 months or with symptom changes 6, 1
Free T4 and T3 levels should be monitored in addition to TSH, as the T3 component can cause disproportionate elevations 4, 3
Critical Safety Concerns
Cardiovascular Risks
Supraphysiologic T3 peaks from DTE absorption can trigger palpitations, tachycardia, and potentially serious cardiac events, especially in patients with underlying heart disease 4, 5
A case report documented acute myocardial infarction in a 32-year-old taking 120 mg Armour Thyroid daily, likely due to hypercoagulable effects 5
Hyperthyroidism from excessive dosing increases cardiovascular event risk 2-3 times through propagation of a hypercoagulable, hypofibrinolytic state 5
Drug Interactions
Never combine with testosterone or anabolic steroids, as this creates synergistic hypercoagulable effects that dramatically increase thrombotic risk 5
The combination of thyroid hormone and androgens can result in myocardial infarction even in young patients without traditional cardiovascular risk factors 5
Bioavailability Considerations
T3 absorption from desiccated thyroid is comparable to synthetic T3, with peak serum T3 occurring at approximately 2 hours versus 2 days for T4-derived T3 8
The rapid T3 absorption creates transient supraphysiologic levels (Free T3 Index of 500 after 75 mcg T3 versus 290 after 3 mg T4), explaining the palpitations and other symptoms 8
When Combination Therapy May Be Considered
For patients who remain symptomatic on adequate levothyroxine monotherapy, a trial of LT4+LT3 combination can be considered, but this should use standardized synthetic preparations, not DTE 3
Reduce LT4 dose by 25 mcg/day and add 2.5-7.5 mcg synthetic LT3 once or twice daily as an appropriate starting point for combination therapy 3
Observational data following 400 patients for approximately 9 years showed no increased mortality or cardiovascular morbidity with LT4+LT3 combination versus LT4 alone when properly dosed 3
Common Pitfalls to Avoid
Do not allow patients to self-administer desiccated thyroid without physician monitoring, as this frequently leads to overdosing and serious complications 5
Avoid using DTE in patients with cardiac disease, atrial fibrillation, or multiple comorbidities due to unpredictable T3 peaks 4, 5
Never start thyroid hormone replacement before ruling out adrenal insufficiency, as this can precipitate adrenal crisis 7, 6
Do not adjust doses more frequently than every 6-8 weeks, as steady state is not reached earlier 6, 1