Selection of thyroid preparations.

Hypothyroidism is gratifying to treat, since the response to hormone replacement therapy is excellent. Synthetic levothyroxine is now considered the drug of choice because its effects are more predictable and reliable than those of other thyroid preparations. The choice of dose is based on clinical effects of treatment and on achieving normal levels of triiodothyronine, thyroxine and thyroid-stimulating hormone (TSH). The availability of a new, ultrasensitive TSH assay has increased the value of TSH assay for monitoring the response to hormone replacement therapy.