A study of the safety of O-isopropoxyphenylmethylcarbamate in an operational field-trial in Iran.

During an operational field-trial which was conducted as a part of the WHO Programme for Testing and Evaluating New Insecticides, a study of the safety of o-isopropoxyphenylmethylcarbamate (OMS-33) was carried out. Clinical observations associated with biochemical studies were performed. Minor reactions to over-exposure to OMS-33 were recorded among some spraymen and a few inhabitants. Their incidence was, in operators, mainly associated with heavy skin contamination and insufficient washing during work, or, in inhabitants, with entering the house while it was being sprayed. No cumulative inhibitory effect could be demonstrated on whole-blood or plasma cholinesterase in operators during the 6-week exposure. A pronounced fall in whole-blood cholinesterase activity during the work and a distinct recovery after exposure ceased was established as a daily pattern of the enzyme's activity fluctuation, erythrocyte cholinesterase being much more sensitive to OMS-33 than plasma cholinesterase. In view of the very marked symptomless daily fluctuation in cholinesterase activity and the absence of cumulative inhibitory effect, the conclusion was reached that routine cholinesterase determination has little if any practical value as an early indication of serious exposure to OMS-33. Minor complaints, from which recovery is rapid, serve as an early indication of over-exposure.OMS-33 can be used safely in malaria eradication programmes provided proper attention is paid to the exercise of those measures of general and personal hygiene which should be practised in any spraying programme.