| Numerous agents (table 1) can impair the absorption of ingested T4, probably by binding T4 in the bowel lumen, resulting in a decrease in serum T4 and increase in serum TSH in treated hypothyroidism (Sherman et al, 1994). By contrast, these agents have a negligible effect if the pituitary-thyroid axis is intact. The interaction can generally be minimized by wide time intervals between the ingestion of T4 and potential inhibitors of absorption. Impaired T4 availability is especially to be avoided where the objective of therapy is TSH suppression in the follow-up treatment of thyroid cancer. |
