Belle Chasse, Louisiana - A US woman has been arrested on a charge of first-degree murder after police say she injected alcohol-based hand sanitiser into the feeding tube of her 17-month-old son, who had Down syndrome.

Twenty-year-old Erika Wigstrom was being held without bond after her arrest on Tuesday.

Plaquemines Parish Sheriff's Commander Eric Becnel says she told police she wanted to end Lucas Ruiz's suffering. Times-Picayune reports that Wigstrom broke down in tears during a court appearance on Wednesday.

Lucas died on January 24.

Becnel says the child had also been poisoned with alcohol in October 2012 while in hospital for the treatment of a heart defect.

Becnel says the child's father, Cesar Ruiz, confessed in that instance, but that Wigstrom now has confessed to poisoning the child both times. - Sapa-AP