ANTITHYROID AGENTS

• Thyroid Agents: Hypothyroidism

  • Levothyroxine (T4)
  • Liothyronine (T3)
  • Liotrix (4:1 ratio of T4:T3)
  • Thyroid Desiccated (USP)

  
• Levothyroxine (T4)


  Synthetic, Thyroid replacement and suppression therapy, Long half-life (7 days) permits once-daily administration (oral/injection), Good stability, low cost, lack of allergenic foreign protein, easy lab measurement of serum levels, Administration produces both hormones as T4 is converted to T3 intracellularly

  
• Liothyronine (T3)


  Synthetic, Short term suppression of TSH, Shorter half-life (24 hours) thus requires multiple daily doses (oral/injection), Higher cost, difficult to monitor conventional lab tests, greater risk of cardiotoxicity, 3-4 times more potent than levothyroxine, C/d: cardiac disease pts
• Liotrix (4:1 ratio of T4:T3)


  Synthetic, Rarely used (only when oral T3 need to be taken), Most expensive
• Thyroid Desiccated (USP)


  Animal, Produce significant elevations in T3 levels and toxicity, Low cost, Protein antigenicity, product instability, variable hormone concentrations, and difficulty in lab monitoring