Rectal administration of propylthiouracil in hyperthyroid patients: Comparison of suspension enema and suppository form

Abstract

Previous studies have described the therapeutic effects of propylthiouracil (PTU) and methimazole in normal subjects after rectal suppositories. The goal of our study was to compare the pharmacokinetic and pharmacologic effects of a suppository and suspension form of PTU given per rectum. Fifteen newly diagnosed hyperthyroid patients of both genders (ages 21 to 55 years) were randomly given the drug as follows: group 1 (n = 7), a single enema (400 mg of PTU in 90 mL of sterile water) and group 2 (n = 8), two suppositories of polyethylene glycol base (200 mg of PTU in each). The pharmacokinetic study revealed earlier time to peak levels (Tmax) and significantly greater maximal peak levels (Cmax) in group 1 than in group 2, (85.71 ± 12.12 minutes vs. 172.5 ± 26.24 minutes for Tmaxand 3.89 ± 0.34 vs. 2.01 ± 0.38 μg/mL, p < 0.05 for Cmax, respectively). However, the area under the curve (635.16 ± 105.71 vs. 377.87 ± 68.09 μg × min/mL) was not statistically different between both groups. Both forms induced a significant decrease in serum free triiodothyronine (FT3) levels and an increase in serum rT3levels shortly after administration. Four subjects reported a bitter taste 5-10 minutes after receiving the drug. PTU can be effectively absorbed via the rectal route. The enema form appeared to provide better bioavailability than the suppository form. However, both preparations exhibited comparable therapeutic effect.