Is there a relationship between the WHO hazard classification of organophosphate pesticide and outcomes in suicidal human poisoning with commercial organophosphate formulations?

The WHO classification of pesticides by hazard is based primarily on the acute oral and dermal toxicity to rats. In several Asian countries there is no legislation against the sale of Class I insecticides. We evaluated if there was an association between the WHO hazard Class I, II or III organophosphate compound and outcomes in human poisoning. Two-hundred and fifty-one patients with mean (SD) age of 30.4 (11.8) years, admitted with symptomatic poisoning and treated with atropine and supportive care, were followed up until death or hospital discharge. The admission pseudocholinesterase level of 818.8 (1368) IU/L indicated significant suppression of cholinesterase activity. Class I compounds were ingested by 126, Class II by 113 and Class III by 12 patients. The hospital mortality rate was 16.7%, 5.3% and 0% with Class I, II and III organophosphate compounds, respectively (P = 0.01). Ventilatory requirements were higher with Class I compared with Class II poisoning (77.0% vs. 54.9%, P < 0.001). Patients with Class I poisoning needed mechanical ventilation for a longer period (10.55 (7.4) vs. 7.0 (5.2) days, P = 0.002). The linear relationship between the WHO hazard class and mortality in acute organophosphate poisoning mandates the restriction of the sale of organophosphate compounds associated with higher lethality amongst humans.