Nursing Pharmacology:  Chapter 30:  Thyroid and Antithyroid Drugs

• Thyroid preparations

  • Synthetic:

    • Levothyroxine

    • Liothyronine

    • Lotrix

  • Animal origin:

    • Dessicated thyroid use is rarely justifiable given the many disadvantages including   protein antigenicity, product instability and variable hormone concentration.

      • Also this form presents difficulty for lab assessment.

  • Preparations of choice: synthetic levothyroxine:

    • Applications

      • Thyroid replacement

      • Suppression therapy

    • bAlthough

      1. Low-cost

      2. Stability

      3. Non-allergenic (no foreign protein)

      4. Serum levels readily obtained

      5. Long half-life (seven days) -- supports once-daily dosing

      6. Since T₄ is converted to T₃ inside the cell, T₄ administration produces both hormones

  • Liothyronine exhibits more activity compared to levothyroxine but not recommended because of:

    1. Shorter half-life (multiple dosing)

    2. More costly

    3. Higher hormonal activity enhances cardiotoxicity (T₃ -- contraindicated in patients with cardiac disease)

    4. Most appropriate use: short-term TSH suppression

Greenspan, F.S., and Dong, B. J.. Histamine, Thyroid and Antithyroid Drugs, in Basic and Clinical Pharmacology, (Katzung, B. G., ed) Appleton-Lange, 1998, pp 619-633.

Wartofsky, L., Diseases of the Thyroid, In Harrison's Principles of Internal Medicine 14th edition, (Isselbacher, K.J., Braunwald, E., Wilson, J.D., Martin, J.B., Fauci, A.S. and Kasper, D.L., eds) McGraw-Hill, Inc (Health Professions Division), 1998, pp 2012-2034