The standard treatment for patients who have attempted suicide by drinking pesticide -- a major problem in parts of rural South Asia and China -- is essentially useless, according to a study.
Activated charcoal, taken orally, has long been prescribed as an antidote for self-inflicted poisoning, as it is thought to absorb toxins in the stomach and prevent them from entering the bloodstream.
But a large clinical study of 4,500 patients, published in Saturday's issue of The Lancet, has found that the carbon powder has no discernible effect.
A team of researchers led by Michael Eddleston of the Scottish Poisons Information Bureau in Edinburgh compared three different treatments for suicide attempts in rural Sri Lanka in 2002 and 2003.
A third of the subjects were given a single, 50-gramme dose of charcoal, and one third were given six 50-gramme doses at four-hour intervals.
For the last third, activated charcoal was omitted entirely from the treatment administered, according to the study.
Mortality rates for all three groups showed no statistically significant difference, varying by less than one percent. On average, 6.8 percent of the patients died as a result of the poisoning.
The percentage needing intubation for breathing, or suffering from seizures, was likewise similar across the three sets of patients, with a slightly lower incidence among those who received multiple doses of charcoal.
Just over half -- 51 percent -- of the subjects ingested industrial insecticides and 36 percent swallowed toxic seeds from yellow oleander, a common roadside plant throughout most of south Asia.
In 2006, the World Health Organisation (WHO) called for restricted access to pesticides and for better training to first-responder medics who treat suicide cases in the countryside in the developing world.
It estimated that nearly 900,000 suicides occurred each year -- more than from homicides and wars combined -- of which 250,000 occurred from poisoning by agricultural chemicals.
In China, Malaysia and Sri Lanka between 60 and 90 percent of all suicides were due to ingestion of pesticides and the incidence was rising in many other countries in Asia, it said.
Compared to industrialised countries, the mortality rate for attempted suicides is 10-to-50 times higher in the rural developing world.
The effectiveness of charcoal has long been debated, and Eddleston's findings will probably not go unchallenged.
A previous study, also conducted in Sri Lanka and published in The Lancet in 2003, determined that multiple doses of activated charcoal halved mortality rates compared to a control group.
But this apparent breakthrough may have been false, as the earlier trial used large doses of atropine, noted Peter and Florian Eyer, researchers at the University of Munich, in a commentary, also in The Lancet.
Atropine is a drug derived from the plant deadly nightshade (Atropa belladonna) that relieves spasms of the gastrointestinal tract, thus reducing secretions of stomach acid.
"Clinical trials to identify effective therapy and new therapeutic inventions with which to prevent these unnecessary deaths are urgently needed," is Eddleston's bleak conclusion.