About The Study

Serious adverse reactions (side effects) to TMP-SMX (Septra), used to treat PCP (pneumonia), increases in people with HIV. This study tested whether the use of NAC could decrease the number of adverse reactions to TMP-SMX.

Study Approach

Participants were randomly assigned to receive either TMP-SMX alone or with NAC (3 grams orally twice daily) one hour prior to each dose of TMP-SMX. NAC was continued for two months and participants were followed for five months. The primary endpoint of the study was the need to stop taking TMP-SMX because of any two side effects: rash, diffuse, severe pruritius (itching) or fever.

Study population

Two hundred and thirty-four people enrolled in the study. They had CD4 counts of 200 or less, and had not taken TMP-SMX since their HIV diagnosis.


One hundred and eighty-one participants were included in the primary analysis; 46 were not included because they had taken less than four weeks of study medication. Twenty-three (24%) participants in the TMP-SMX group and 20 (22%) in the NAC group stopped taking TMP-SMX due to rash, severe itching and fever. The average time to rash was two weeks and did not differ between the two groups. Equal numbers of participants in each group stopped taking TMP-SMX due to any reason. The trial was terminated by the Safety & Efficacy Review Committee at the interim analysis based on lack of efficacy.


The use of oral NAC (6 grams/day) did not decrease the incidence of hypersensitivity reactions to TMP-SMX in people with HIV.