Clinical review 129: Oral cholecystographic agents and the thyroid.

Oral cholecystographic agents (OCAs) are known to affect thyroid hormone metabolism by acting as potent inhibitors of type I and type II deiodinases, blocking the conversion of T(4) to T(3) and rT(3) to T(2). In addition, iodine released from the drug blocks thyroid gland secretion of thyroid hormone. These properties make OCAs a potentially useful drug therapy in patients with hyperthyroidism and other thyrotoxic disorders. Short-term treatment with OCAs rapidly reduces serum T(3) levels, with a lesser effect on T(4) levels. OCAs are not useful for long-term treatment, which is usually followed by exacerbation of hyperthyroidism with continued use. The lack of significant side effects makes these drugs an excellent short-term option in situations where a rapid clinical improvement is critical.