Levothyroxine monitoring therapy with

Therapy with levothyroxine is very safe, provided that thyroid hormone levels are monitored and maintained within the normal range. Excess doses of T4 are associated with a loss of bone mass. A meta-analysis of 41 controlled studies on the impact of thyroid hormone therapy on bone mineral density (Uzzan et al., 1996) has shown that doses of T4 that suppress thyrotropin (TSH) secretion are associated with a significant loss of bone in the lumbar spine and hip in postmenopausal women. Another review of the evidence of the thyroid hormone effect of on skeletal integrity concluded that hyperthyroidism and the use of thyroid hormone to suppress TSH seem to have an adverse effect on bone, especially in postmenopausal women (Greenspan and Greenspan, 1999) however, thyroid hormone replacement seems to have a minimal effect on bone. 

Although liothyronine (T3) is three to four times more potent than levothyroxine, it is not recommended for routine replacement therapy because of its shorter half-life (24 hours), which requires multiple daily doses its higher cost and the greater difficulty of monitoring its adequacy of replacement by conventional laboratory tests. Furthermore, because of its greater hormone activity and consequent greater risk of cardiotoxicity, T3 should be avoided in patients with cardiac disease. 

The average maintenance dose for most adults is about 125 mcg/day, but there is a wide range of replacement doses, necessitating individualized therapy and appropriate monitoring to determine an appropriate dose. Patients with subcUnical hypothyroidism and marked elevations in TSH (greater than 10 milli-intemational units per liter [mlU/L]) and high titers of TSAh or prior treatment with sodium iodide 131 may benefit from treatment with levothyroxine. 

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