The propose of this study is to determine whether N-acetylcysteine is effective in reversing the changes in thyroid hormones seen in critical illness, known as the low T3 syndrome.

The low T3 syndrome or nonthyroidal illness is characterized by low levels of T3, normal or high normal levels of rT3, low or normal levels of T4 and inappropriately normal or low levels of TSH. These changes affect up to 75% of patients and have prognostic implications.

Interleukin-6 (IL6) seems to have a causative role in the pathogenesis of nonthyroidal illness. There is evidence that the reduction in serum T3 was inversely associated with serum IL-6, while the rT3 have a positive association. The mechanism of action of cytokines on the metabolism of thyroid hormones has not been determined and the potential role of cytokines on the deiodases has been the focus of research.

In a cell culture model study, IL-6 was able to suppress the conversion of T4 to T3 by deiodases type 1 and 2 and stimulate the inactivation of T3 by deiodase type 3, a situation similar to nonthyroidal illness. The use of N-acetylcysteine prevented this alterations, been consistent with the hypothesis that IL6 inhibits the function of the deiodases by increasing the oxygen reactive species and by consuming gluthathione or some gluthathione dependent cofactor.

Considering the absence of human studies evaluating the use of N-acetylcysteine in nonthyroidal illness, the aim of this study is to investigate whether NAC has in vivo effect on changes of thyroid hormones.

Inclusion Criteria:

• diagnosis of acute myocardial infarction with less than 12 hours of evolution
• reperfusion therapy (primary angioplasty)

Exclusion Criteria:

• Thyroid disease
• Chronic renal disease with renal replacement therapy
• hepatic insufficiency
• immunosuppression

Adverse reactions were collected during drug infusion period (48 hours)