The most changed behaviours were social communication and play, speech and language, calm and focus, repetitive behaviour and coping skills, the researchers said.
"During the time the children were on suramin, benefit from all their usual therapies and enrichment programs increased dramatically," said lead author Robert K. Naviaux, Professor at the University of California San Diego.
Importantly, suramin caused significant improvements in language and social interaction in a 14 year old boy who had not spoken a complete sentence in 12 years.
"We had four non-verbal children in the study, two 6 year olds and two 14 year olds. The six year old and the 14 year old who received suramin said the first sentences of their lives about one week after the single suramin infusion. This did not happen in any of the children given the placebo," Naviaux added.
The findings were reported in the Annals of Clinical and Translational Neurology.
According to Naviaux, autism is caused by metabolic dysfunction or impaired communication between cells in the brain, gut and immune system, resulting from abnormal persistence of the cell danger response (CDR) – a natural and universal cellular reaction to injury or stress.
Suramin works by inhibiting the signalling function of adenosine triphosphate (ATP) – a small molecule released from the cell as a danger signal.
When CDR is activated, the effect of extracellular ATP is similar to a warning siren that never stops.
Suramin silences the siren, "signalling the cellular war is over, the danger has passed and cells can return to 'peacetime' jobs like normal neurodevelopment, growth and healing", Naviaux noted.
However, the therapeutic benefit of suramin was temporary, as the improvements peaked and then gradually faded after several weeks as the single dose of suramin wore off, the researchers said.