Snake Venom Antiserum

Indications

Snake Venom Antiserum is used for: Snake bites, Snake Venom Antiserum is indicated for bites caused by Cobra, Common Krait, Russell's Viper and Saw-Scaled Viper, where the patient presents with one or more of fallowing visible clinical signs and symptoms of envenomation – 1. Local envenomation- a) Presence of bite marks with or without oozing of blood, blistering and change in color of skin. b) Rapidly progressive or massive swelling involving more than half of the bitten limb within few hours of bite (without tourniquet) c) Development of enlarged tender lymph nodes draining the bitten part within couple of hours after bite 2. Systemic envenomation- a) Neurotoxic syndrome- signs of neuro-paralysis like blurring of vision, double vision, and difficulty in swallowing, sleepy feeling, drooping of head, slurring of speech and the voice may become indistinct with shallow breathing, ptosis, ataxia, respiratory paralysis and generalized flaccid paralysis. b) Hemotoxic syndrome- spontaneous systemic bleeding, nausea, vomiting, abdominal pain and abdominal tenderness suggestive of gastro-intestinal or retro-peritoneal bleed and/or renal damage, coagulopathy detected by 20 min WBCT with or without external bleeding and shock.

Adult Dose

As of now Antivenom is the only specific antidote for snake envenomation and prompt administration of adequate dose of Antiserum is of paramount importance for neutralization of unbound circulating snake venom components for early response to treatment. Any delay in administration may result in increased dose requirement and decreased effectiveness. As the clinical signs can vary due to many factors such as type of snake, time of reporting after bite, size of snake, amount of venom injected during bite, seasonal & regional variation in venom composition etc., no accurate dosage can be recommended. However, considering the average quantity of venom injected by snake at the time of bite and degree of envenomation. It is recommended to administer initial dose of 5-10 vials of Antiserum by slow intravenous infusion either undiluted at a speed of not more than 2 ml/minute or after dilution with normal /glucose saline at a rate of 5-10 ml/kg body weight over 1 hour. Constant monitoring of the vital signs at frequent intervals during initial 1 hour is recommended. Requirement of further dosing depends on extent of reversal of coagulopathy confirmed after 6 hours of antiserum administration by WBCT in haemotoxic bite or if symptoms persist or worsen or in respiratory failure in neurotoxic bite after 1 hour of antiserum administration. If the blood is still incoagulable or no signs of reversal of paralysis are seen, a further dose of 5-10 vials of antiserum should be administered by slow IV route only. Administration by IM or locally around the bite wound is not recommended. In the majority of cases of both neurotoxic and haemotoxic bites, total dose of 15-20 vials is adequate unless a proven recurrence of envenomation is established. In such a scenario, further doses can be given as per clinical condition of the patient. Hypersensitivity skin test has no predictability value and hence should not be used.

Child Dose

Children should receive the same dose as adults. As of now Antivenom is the only specific antidote for snake envenomation and prompt administration of adequate dose of Antiserum is of paramount importance for neutralization of unbound circulating snake venom components for early response to treatment. Any delay in administration may result in increased dose requirement and decreased effectiveness. As the clinical signs can vary due to many factors such as type of snake, time of reporting after bite, size of snake, amount of venom injected during bite, seasonal & regional variation in venom composition etc., no accurate dosage can be recommended. However, considering the average quantity of venom injected by snake at the time of bite and degree of envenomation. It is recommended to administer initial dose of 5-10 vials of Antiserum by slow intravenous infusion either undiluted at a speed of not more than 2 ml/minute or after dilution with normal /glucose saline at a rate of 5-10 ml/kg body weight over 1 hour. Constant monitoring of the vital signs at frequent intervals during initial 1 hour is recommended. Requirement of further dosing depends on extent of reversal of coagulopathy confirmed after 6 hours of antiserum administration by WBCT in haemotoxic bite or if symptoms persist or worsen or in respiratory failure in neurotoxic bite after 1 hour of antiserum administration. If the blood is still incoagulable or no signs of reversal of paralysis are seen, a further dose of 5-10 vials of antiserum should be administered by slow IV route only. Administration by IM or locally around the bite wound is not recommended. In the majority of cases of both neurotoxic and haemotoxic bites, total dose of 15-20 vials is adequate unless a proven recurrence of envenomation is established. In such a scenario, further doses can be given as per clinical condition of the patient. Hypersensitivity skin test has no predictability value and hence should not be used.

Renal Dose

Administration

Snake Venom Antiserum is administered intravenously either undiluted at the rate of not more than 1ml per minute or is diluted in 500ml of intravenous fluid (either Sodium Chloride Injection or 5% Dextrose Injection) and administered as rapidly as tolerated over 1-2 hours. While diluting the Snake Venom Antiserum, mix by gentle swirling rather than shaking to avoid foaming. Additional infusions should be repeated hourly until progressive swelling in the bitten part ceases and systemic signs and symptoms disappear. When an adequate dosage is achieved, the improvement in patient's clinical signs are often seen.

Contra Indications

There are no known contraindications for the administration of Antivenom. Person who is proven to be allergic to equine antisera.

Precautions

Proper precautions are necessary while dealing with persons with a known hypersensitivity to constituents of product. Few doctors prefer to premedicate patients with Inj. Adrenaline 0.25 ml s/c to prevent possibility of adverse reactions. In haemotoxic bites, IM injections should be avoided till correction of coagulopathy to avoid formation of haematoma and oozing of blood. Not for local administration on bitten area. In patients having tourniquet, it should be released slowly only after start of Antivenom administration. Considering the risk associated with snake bite envenomation, pregnancy is not a contraindication for the administration of Snake Venom Antiserum subsequent to bite.

Pregnancy-Lactation

Considering the risk associated with snake bite envenomation, pregnancy is not a contraindication for the administration of Snake Venom Antiserum subsequent to bite.

Interactions

Increased risk of hypoglycaemia when used in combination w/ sulfonylureas or insulin.

Adverse Effects

Side effects of Snake Venom Antiserum : The immediate reaction (shock & anaphylaxis) usually occurs within 30 minutes. Symptoms and signs may develop before the needle is withdrawn and include urticaria, itching, fever, chills or rigor, nausea, vomiting, diarrhoea, abdominal cramps, tachycardia, hypotension, bronchospasm, and angioedema. Serum sickness usually occurs 5 to 24 days after administration. The usual symptoms and signs are fever, urticaria, edema, nausea and vomiting. Occasionally neurological manifestations develop. Pain and muscle weakness are frequently present.

Mechanism of Action

Passive immunization, antivenoms are in- jected to neutralize snake venoms in the patient’s blood circulation.