In short Article

Interactions with drugs used for thyroid disorders

Thyroid and drugs part 3

Drugs used to treat thyroid disorders can interact with other drugs. Interactions with thyromimetics (levothyroxine and liothyronine) can be subdivided into interactions with drugs that affect the bioavailability of the thyromimetics, drugs that accelerate the breakdown of thyromimetics and drugs that change the required dosage of thyroid hormones. Finally, the effect of drugs can be influenced by changes in the thyroid gland’s functioning. Knowledge about the pharmacological background of the interactions can be used to address or avoid these interactions in practice.

  • The gastro-intestinal absorption of thyromimetics (levothyroxine and liothyronine) can be reduced by various drugs. The effect of such interactions can often be minimised by avoiding simultaneous administration of the drugs. 
  • The breakdown of thyromimetics can be increased by enzyme inductors, which often mean that a higher dosage of levothyroxine or liothyronine will be needed.
  • Oral oestrogens can change the amount of thyromimetics needed by influencing the concentration of thyroxine-binding globulin. 
  • Both thyromimetics and thyreostatic drugs interact with vitamin K antagonists, which means that starting or discontinuing thyroid drugs must be reported to the thrombosis service. 
  • The effect of nearly all interactions must be monitored by determining the thyroid values 6 weeks after a patient starts using the drug combination or after their dosage is changed, and to a lesser extent by assessing the clinical picture.

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  • Suzanne de Klerk
  • Loes Ariaans, MSc
  • Gideon Lansbergen
  • Thiemo F. Veneman
  • Sander D. Borgsteede