Which of the following is an anti-thyroid drug that should be discontinued prior to a thyroid uptake test?

The drug that should be discontinued prior to a thyroid uptake test is Propylthiouracil. This medication is classified as an anti-thyroid drug, which works by inhibiting the synthesis of thyroid hormones. When conducting a thyroid uptake test, often the goal is to assess the functioning of the thyroid gland by measuring how effectively it absorbs iodine.

If Propylthiouracil is present in the body, it can skew the results of the test by artificially reducing the gland's ability to uptake iodine. This can lead to misleading interpretations of the thyroid's function, which is why it is crucial to suspend its use before testing.

Other medications and substances mentioned, such as Synthroid, potassium perchlorate, and Lugol's solution, do interact with thyroid function but in different ways or do not have the same impact on uptake testing. Synthroid, as a thyroid hormone replacement, is not an anti-thyroid drug; potassium perchlorate is used to block iodine uptake but isn't commonly considered in the context of thyroid uptake testing. Lugol's solution, which contains iodine, can actually saturate the thyroid and also affect results but doesn't function the same way as an anti-thyroid medication.