Which brand of levothyroxine (T4) has the least amount of fillers?

Levothyroxine Formulations with Least Amount of Fillers

Tirosint-SOL (levothyroxine sodium oral solution) has the least amount of fillers, containing only three ingredients: levothyroxine, water, and glycerol. 1

Comparison of Levothyroxine Formulations

Tablet Formulations

Standard levothyroxine tablets contain multiple inactive ingredients:

• Microcrystalline sodium
• Light magnesium oxide
• Sodium starch glycolate
• Sodium stearyl fumarate
• Various color additives depending on strength 2

These fillers can potentially affect absorption, especially in patients with gastrointestinal conditions or sensitivities.

Softgel Capsule Formulations

Softgel capsules have fewer ingredients than standard tablets and may provide:

• Better absorption compared to tablets 3
• More consistent TSH levels 4
• Improved bioavailability in patients without malabsorption 3

Liquid Formulations

Tirosint-SOL (liquid levothyroxine) has:

• Only three ingredients (levothyroxine, water, glycerol) 1
• Superior absorption profile even when taken closer to meals 5
• Better normalization of thyroid function in patients with absorption issues 1

Clinical Implications of Formulation Choice

Absorption Considerations

• Absorption of orally administered levothyroxine ranges from 40% to 80% 2
• Formulations with fewer fillers may have more consistent absorption profiles
• Liquid formulations show faster absorption than tablets or softgel capsules 5

Patient-Specific Factors

Formulations with fewer fillers are particularly beneficial for:

• Patients with gastrointestinal disorders (gastroparesis, SIBO, gastritis) 1
• Those with multiple food and medication sensitivities 1
• Patients with suboptimal TSH control on tablet formulations 3

Bioequivalence Concerns

• FDA protocol for establishing bioequivalence of levothyroxine formulations has been criticized by professional endocrinology associations 6
• Even small differences between formulations can cause significant changes in TSH levels 6
• Generic substitutions may not provide the same clinical effect despite being deemed "bioequivalent" 6

Practical Recommendations

1. For patients with absorption issues or multiple sensitivities, consider Tirosint-SOL (liquid formulation) with minimal fillers 1

2. For patients who prefer a solid dosage form but need fewer fillers, softgel capsules may be appropriate 3, 4

3. When switching between formulations:

   • Monitor TSH levels closely
   • Adjust dosage if necessary
   • Maintain patients on the same preparation when possible 6

4. Be aware that formulation changes may require dose adjustments, even when switching to preparations with fewer fillers 6

Important Considerations

• Levothyroxine dosage requirements may increase during early pregnancy 7
• Elderly patients are more sensitive to thyroid hormone effects and may require lower doses 2
• Patients with cardiovascular disease require careful monitoring when changing formulations 2

By selecting formulations with minimal fillers like Tirosint-SOL, clinicians can optimize absorption and potentially improve therapeutic outcomes, especially in patients with absorption issues or multiple sensitivities.