Efficacy of anti-scorpion venom serum over prazosin in severe scorpion envenomation: Is the current evidence enough?

AB Thirunavukkarasu, V Chandrasekaran 
 Department of Pediatrics, Sri Lakshmi Narayana Institute of Medical Sciences (SLIMS), Puducherry, India

Correspondence Address:
A B Thirunavukkarasu
Department of Pediatrics, Sri Lakshmi Narayana Institute of Medical Sciences (SLIMS), Puducherry
India

Full Text

Sir,

We read the article on "Efficacy of anti-scorpion venom serum over prazosin in the management of severe scorpion envenomation" by Natu et al[1] with interest. In recommending scorpion antivenin over prazosin, the author has offered a radical change in the existing management guidelines for scorpion sting. [2],[3]

However, we would like to raise certain points regarding the study. The process of assigning patients to individual groups has not been explained clearly. There is a possibility of potential allocation bias which could have influenced the results. Increasing pain at the sting site has been taken as the first sign of recovery though it is not a consistent feature.

The author has also proposed a clinical composite score to assess the efficacy of the therapeutic regimen. We feel that sweating is one of the evolving spectrum of symptoms (seen in the first 6-12 hours of cholinergic phase) and does not reflect the severity in a true sense, and moreover, the grades suggested are subjective. Inclusion of factors like priapism will lead to gross differences in scores between genders for the same manifestations. As the proposed composite scoring is not validated, we feel it is not scientific to base treatment decisions (dosing of antivenin) on that score and hence the methodology becomes questionable.

The author mentions that all groups are comparable, whereas the variation in the reporting time in antivenin group is higher when compared to other groups. There is a chance that the improved efficacy of the antivenin group can be due to late arrival of patients (either because of mild symptoms or previous treatment). The reasons for late arrival and any previous prazosin therapy before recruitment have not been mentioned.

Prazosin is an alpha blocker which specifically helps in peripheral circulatory failure and in myocarditis by decreasing the preload and after load. Case fatality rates have declined from 25-30% to less than 1% following prazosin use. [4] Scorpion antivenin acts by reducing serum venin concentration. However, its clinically effectiveness is yet to be conclusively proven. [5]

Prazosin is a cheap drug available universally even in peripheral health care settings, which is in contrast to scorpion antivenin which is costly, has no proven efficacy, has little or no cardioprotective role, needs monitoring during administration due to significant side effects and is not freely available throughout India. [2],[3] A meta-analysis published after reviewing results from 69 trials regarding the use of scorpion antivenin has concluded that there is little evidence of improved clinical outcomes. [5]

We strongly disagree with the author's recommendation that prazosin should be reserved only for patients presenting with hypertension and pulmonary edema. It has been extensively studied and proven that early prazosin therapy is cardioprotective and improves survival. [2],[3],[4]

We feel that prazosin is still the first-line therapy for scorpion sting as concluded by numerous trials and the current study does not warrant its stoppage as recommended by the author. Large-scale multicentric trials are needed to find out the efficacy of scorpion antivenin.

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