Comparative Pharmacology
Head-to-head clinical analysis: LEVOTHYROXINE versus TIROSINT.
Peer-Reviewed Evidence
Head-to-head clinical analysis: LEVOTHYROXINE versus TIROSINT.
Levothyroxine vs TIROSINT
Comparing the clinical profiles, pharmacokinetic behaviors, and safety indices of these two therapeutic agents.
Levothyroxine is a synthetic form of thyroxine (T4) that is converted to triiodothyronine (T3) in peripheral tissues. T3 binds to thyroid hormone receptors in the nucleus, regulating gene transcription and increasing metabolic rate, protein synthesis, and oxygen consumption.
Tirosint is a synthetic form of levothyroxine (T4), which is converted to triiodothyronine (T3) in peripheral tissues. T3 binds to thyroid hormone receptors in the nucleus, modulating gene transcription to increase metabolic rate, protein synthesis, and oxygen consumption.
1.6 mcg/kg orally once daily, adjusted based on TSH levels; typical adult dose 50-200 mcg/day.
Initial dose 1.6 mcg/kg orally once daily, adjusted based on TSH levels. Typical maintenance dose 50-200 mcg/day.
None Documented
None Documented
Clinical Note
moderateLevothyroxine + Sulfisoxazole
"The metabolism of Sulfisoxazole can be decreased when combined with Levothyroxine."
Clinical Note
moderateLevothyroxine + Erythromycin
"The metabolism of Erythromycin can be decreased when combined with Levothyroxine."
Clinical Note
moderateLevothyroxine + Cyclosporine
"The metabolism of Cyclosporine can be decreased when combined with Levothyroxine."
Clinical Note
moderateLevothyroxine + Fluconazole
7 days (euthyroid); prolonged in hyperthyroidism (3-4 days) and shortened in hypothyroidism (9-10 days); clinical effects persist for weeks after discontinuation due to slow elimination.
Terminal half-life approximately 7 days in euthyroid individuals; prolonged in hypothyroidism (up to 9-10 days) and shortened in hyperthyroidism (3-4 days). Clinical context: steady-state reached in 4-6 weeks; dosage adjustments require 6-8 weeks for full effect.
Primarily renal (approximately 50% as unchanged drug and metabolites, mainly glucuronide and sulfate conjugates); minor biliary/fecal excretion (<20%).
Renal (approximately 30-40% as unchanged drug and metabolites, primarily glucuronide and sulfate conjugates); fecal (approximately 20-30% via bile); total clearance is low (~0.05 L/hr/kg).
Category A/B
Category C
Thyroid Hormone
Thyroid Hormone
"The metabolism of Fluconazole can be decreased when combined with Levothyroxine."