Forty-nine patients with Graves' disease were randomly divided into two groups. One group received propylthiouracil, 150 mg every eight hours, and the other group received propylthiouracil, 450 mg as a single daily dose. All patients' conditions were evaluated clinically and chemically at two-week intervals. The response to the divided dosage schedule was prompt and predictable, and by ten weeks all but one patient had achieved remission. The group that received the single daily dose regimen responded less favorably, and at ten weeks ten patients had failed to achieve remission (P<.001). However, when these patients' regimens were switched to the every-eight-hour schedule, all but one patient became euthyroid in an additional four weeks.
(JAMA 239:2457-2459, 1978)
Gwinup G. Prospective Randomized Comparison of Propylthiouracil. JAMA. 1978;239(23):2457–2459. doi:10.1001/jama.1978.03280500053019