Projected serum T3 levels according to mathematical model: (A–C) Modeling of 50 mcg LT3 administered on a thrice (A), twice (B), or single (C) daily regimen. (D) Hypothetical 72.5 kg hypothyroid patient treated with 112 mcg LT4 alone, being transitioned to LT4/LT3 therapy at a 16:1 weight/weight combination therapy, that is, LT3 dose of 3.25 mcg twice daily and LT4 dose of 92.5 mcg daily; (E) same as (D) except that the LT4 dose was reduced by 25 or 50 mcg and substituting with 5 or 10 mcg LT3 on twice daily (E, F), respectively (i.e., to an LT3 dose of 5 or 10 mcg twice daily and LT4 dose of 88 or 62 mcg daily, respectively); dashed line is the mean concentration of T3. Modified from Van Tassell et al. (45). LT3, liothyronine; LT4, levothyroxine.