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 T₄ to T₃ and rT₃ to T₂. 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 T₃ levels, with a lesser effect on T₄ 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.