Police identified the victim as 57-year old Leela Karkera in an unnatural death report, according to the Times of India.
Karkera was reportedly unable to tell the difference between the packaging of the rat poison and toothpaste.
She was rushed to a private hospital immediately for treatment but died on Sunday.
The incident took place in the Indian port of Malpe, near Udupi city on the Karnataka coast.
It is reportedly fairly common to mistake a specific brand of rat poison for toothpaste due to similarities in packaging. There is no antidote for the poison.
In 2012, two young children in Puducherry died after accidentally brushing their teeth with the poison.
One of the victims, a 5-year old girl, died of liver failure almost a week after using the poison by mistake.
The other, a 3-year old boy, also died of liver failure, reported the Times of India.
The year before, a 3-year old girl was admitted to hospital for the same accident, but doctors were able to save her after more than two weeks of treatment.
The Indian Journal of Critical Care Medicine called for the Ratol brand rat poison to be banned in Indian households in 2015.
They cited fatal doses of yellow phosphorus and the common mistaking of Ratol for toothpaste as reasons for the ban.
Yellow phosphorus poisoning causes acute liver failure, and as there is no antidote, the only definitive treatment is a liver transplant.
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