AScVS and/ or Prazosin for Scorpion Envenomation

Red Scorpion (Mesobuthus Tamulus Concanesis Pocock) sting is a common medical emergency in the coastal regions of India and is a cause for considerable morbidity and mortality.

Signs and symptoms show either cholinergic or adrenergic predominance. Cholinergic symptoms are profuse sweating, priapism, bradycardia, increased salivary and bronchial secretions and vomiting. Adrenergic symptoms are transient hypertension followed by hypotension, tachycardia, tachypnoea, pulmonary edema and circulatory failure in later stages. Scorpion venom blocks voltage dependent inactivation of sodium channels, resulting in intense persistent voltage depolarization of autonomic nerves with massive release of catecholamines from adrenal medulla and parasympathetic and sympathetic nerve endings.

Prazosin a selective alpha-1 blocker is used as the treatment for scorpion sting, which can only counteract the manifestations of sympathetic over-activity. Experimentally and clinically it is seen that scorpion venom stays in the body for 24-36 hours, as Prazosin does not neutralize the venom, 3 hourly round the clock doses of prazosin and continuous I.C.U. monitoring is necessary with alpha blocker therapy. However, ideal treatment modality remains neutralization of venom in the systemic circulation.

Since 1997 enzyme refined AScVS ( Monovalent Anti-scorpion venom serum against Mesobuthus tamulus concanesis Pocock.) has been made available by Haffkine Biopharmaceuticals, Mumbai for field use. Throughout the konkan(western coastal Maharashtra, India) area the same species of scorpions responsible for fatal envenomation is found.

From 1997-2002, 48 patients of serious scorpion envenomation were treated with AScVS(1). Based on this experience a clinical scoring system for dose requirement was evolved based on sweating, pulse rate, respiratory rate, blood pressure, CNS effects and presence of priapism. In our experience computed doses given as intravenous bolus are more effective and successfully ameliorated signs and symptoms in all patients. Subsequently 16 patients were given treatment with either AScVS (n=8), Prazosin (n=5) and a combination of both (n=3) so as to compare the effects of these available treatment modalities. It was found that the patients receiving either AScVs or a combination showed a complete recovery approximately within 4 hours of onset of therapy as against patients receiving Prazosin, who required 16 hours for recovery. There was no mortality in any of the group. There was not a single incidence of anaphylaxis after administration of AScVS. Release of adrenaline in the systemic circulation by scorpion sting itself appears to be protective against the danger of anaphylaxis. The label on the AScVS vials states that the maximum dose is 3 vials, which can be given either intramuscular or by intravenous route. However we used AScVS as slow bolus intravenously and dose was decided clinically depending upon the severity of the patient condition. (maximum 10-15vials.) Based on this experience, an open labeled, randomized controlled parallel group clinical trial has been initiated. Eighty-three patients have been recruited so far, 28 patients each, in AScVS and AScVS + prazosin group and 27 patients in Prazosin group, two patients out of 27 in Prazosin group were withdrawn as both the pediatric patients (around 12 years old) developed pulmonary edema after few hours, so AScVS had to be given. The onset of relief (based on composite score) with AScVS or combination of AScVS with prazosin was early and complete recovery occurred at 4.14+/- 1.6 hrs. and 3.46+/- 1.10hours. However, in patients receiving only prazosin, the clinical score was found to worsen initially, followed by a gradual improvement and subsequent complete recovery, at 19.28 +/- 5.03 hrs. (p<0.001 vs AScVS). Recovery time with AScVS is much shorter because after complete neutralization of venom, fresh secretion of catecholamines stop and adrenaline and nor-adrenaline which are already in circulation have action as short as 1 to 2 minutes. These findings appear consistent with our clinical experience and indicate that in the near future AScVS would evolve as a safe, efficacious and life saving treatment modality for patients with severe scorpion envenomation. Use of clinical scoring system can enable the clinician to select the optimum dose of AScVS to be administered.

Neutralization of venom is thus proved to be better than therapy for complications, akin to the dictum 'prevention is better than cure'.

References:

1. Natu VS, Murthy RKK, Deodhar KP. Efficacy of species specific Antiscorpion venom serum (AScVS) against severe, serious scorpion stings (mesobuthus tamulus concanesis pocock.)-An experience from rural hospital in western Maharashtra. JAPI, 2006; 54: 283-7.