(Phoenix Pharmaceutical) Thyrozine Powder is used for correction of conditions associated with hypothyroidism in horses. Thyrozine Powder contains levothyroxine sodium. Each level teaspoon delivers approximately 12 mg of levothyroxine sodium, USP. Equine Thyroid Supplement can be administered by top dressing ration once per day or in divided doses. Levothyroxine sodium. Compare to Thyro-L.