No evidence that oximes are a useful treatment for organophosphate pesticide poisoning

Many thousands of people die every year because of poisoning by organophosphate pesticides. Most of the deaths are in developing countries. Drugs known as oximes are used as part of the standard recommended treatment, even though many doctors have said that they don't seem to have any benefit. This research has produced mixed evidence. Many of the studies had substantial limitations. Generally, the studies done to date do not support the routine use of oximes, however, they cannot exclude that there would be some doses or situations where a benefit would occur. The reviewers found that not enough research has been done to see whether oximes are actually effective or to define the doses that are more likely to be helpful. More research is needed before any firm conclusions can be drawn.

Authors' conclusions: 

Current evidence is insufficient to indicate whether oximes are harmful or beneficial. The WHO recommended regimen (30 mg/kg pralidoxime chloride bolus followed by 8 mg/kg/hr infusion) is not supported. Further RCTs are required to examine other strategies and regimens. There are many theoretical and practical reasons why oximes may not be useful, particularly for late presentations of dimethyl OP and those with a large excess of OP that simply re-inhibits reactivated enzymes. Future studies should screen for patient sub-groups that may benefit and may need flexible dosing strategies as clinical effectiveness and doses may depend on the type of OP.

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Background: 

Acute organophosphorus pesticide poisoning causes tens of thousands of deaths each year across the developing world. Standard treatment involves administration of intravenous atropine and oxime to reactivate inhibited acetylcholinesterase. The clinical usefulness of oximes, such as pralidoxime and obidoxime, has been challenged over the past 20 years by physicians in many parts of the world.

Objectives: 

To quantify the effectiveness and safety of the administration of oximes in acute organophosphorus pesticide-poisoned patients.

Search strategy: 

We searched both English and Chinese databases: Cochrane Injuries Group Specialised Register, Cochrane Central Register of Controlled Trials (The Cochrane Library), MEDLINE (Ovid SP), EMBASE (Ovid SP), ISI Web of Science: Science Citation Index Expanded (SCI-EXPANDED), ISI Web of Science: Conference Proceedings Citation Index-Science (CPCI-S) and the Chinese language databases CNKI and WANGFANG. All searches were run in September 2009.

Selection criteria: 

Articles that could possibly be RCTs were retrieved to determine if they were randomised.

Data collection and analysis: 

The published methodology of three RCTs was not clear. We contacted the principal authors of these, but did not obtain further information.

Main results: 

Seven pralidoxime RCTs were found. Three RCTs including 366 patients studied pralidoxime vs placebo and four RCTs including 479 patients compared two or more different doses. These trials found quite disparate results with treatment effects ranging from benefit to harm. However, many studies did not take into account several issues important for outcomes. In particular, baseline characteristics were not balanced, oxime doses varied widely, there were substantial delays to treatment, and the type of organophosphate was not taken into account. Only one RCT compared the World Health Organization (WHO) recommended doses with placebo. This trial showed no clinical benefits and a trend towards harm in all sub-groups, despite clear evidence that these doses reactivated acetylcholinesterase in the blood.

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