Levothyroxine

Levothyroxine

Levothyroxine is a synthetic preparation of thyroxine (T4) and is the treatment of choice for the routine management of hypothyroidism. The most common cause of hypothyroidism is autoimmune thyroiditis  This drug is given once daily because of its long half-life. A therapeutic state is achieved in 6-8 weeks. The goal of treatment in thyroid disease is to restore thyroid levels to a normal level.

Laboratory tests

Order TSH first and, if elevated, order free T3 and T4. Order TSH-receptor antibodies to confirm Hashimoto’s thyroiditis

• TSH elevated (> 6.0 mlU/L) with low serum free T4 = hypothyroidism
• Antimicrosomal antibodies elevated = Hashimoto’s thyroiditis (Gold Standard for diagnosing Hashimoto’s thyroiditis)

Therapy monitoring

• Clinical and laboratory evaluations should be performed at 6-8 week intervals while titrating
• High TSH and Low T4 = hypothyroidism
• Laboratory monitoring is done annually once a euthyroid state is established
• Upper normal limit of TSH in elderly is 7.5 mU/L

Replacement recommendations in healthy young patients

**adults need 1.6mcg/kg/day**

**based on ideal body weight, not actual body weight**

Levothyroxine tablets dosages

• 25 mcg
• 50 mcg
• 75 mcg
• 88 mcg
• 100 mcg
• 112 mcg
• 125 mcg
• 137 mcg
• 150 mcg
• 175 mcg
• 200 mcg
• 300 mcg

 Replacement recommendations in middle age/older adults/elderly

• Patients 50-60 years old= start at 50 mcg daily
• Older adults and elderly, multiple comorbidities, and cardiac disease= start at 25mcg daily
• Small decreases may be needed as the patient ages