Introduction:

The absorption of levothyroxine (LT4) is affected by medications and food. Consumption of Ilex paraguariensis (IP) as an infusion with hot water (mate) or cold water (tereré) is popular in the Southern Cone of Latin America.

Objective:

To compare LT4 absorption with IP versus plain water.

Materials and Methods:

A pharmacokinetic study was conducted in healthy euthyroid volunteers. A dose of 1000 µg LT4 was administered with mate, plain water, and tereré, respectively. Serial measurements of total blood thyroxine (TT4) were performed, and mean peak plasma concentrations of TT4 (Cmax), mean time to reach Cmax (Tmax), 24-hour change in thyroid-stimulating hormone (TSH) (ΔTSH), and estimated percentage of LT4 absorption (%Abs) were compared. The protocol was approved by an Ethics Committee.

Results:

Twenty volunteers completed the study. Differences in Cmax, Tmax, and %Abs between LT4 with plain water and LT4 with mate were statistically significant (Cmax: 17.38 µg/dL vs 14.95 µg/dL, p=0.02; Tmax: 3h vs 4.2h, p=0.03; %Abs: 104.83% vs 76.42%, p=0.05). No statistically significant differences were found when comparing LT4 with plain water versus LT4 with tereré (Cmax: 16.36 µg/dL, p=0.29; Tmax: 4 h, p=0.09; %Abs: 90.76%, p=0.15). Regarding ΔTSH, LT4 with plain water resulted in 1.1 µIU/mL versus LT4 with mate 1.09 µIU/mL (p=0.96) or LT4 with tereré 1.35 µIU/mL (p=0.31), without statistically significant differences.

Conclusions:

LT4 absorption was lower when administered with mate, but not with tereré, compared with plain water.

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