Snakebite and Anti-Snake Venom: The Evidence Behind the Protocol

It is a July night in a primary health centre near Kundapura, and the rain has not stopped for three days. A 35-year-old paddy farmer is carried in by his brothers. He was walking along the edge of his field at dusk when something bit his ankle. Nobody saw the snake clearly. His foot is swollen and very painful, and there is a small ooze of blood from the bite marks. His brother asks, “Doctor, was it a poisonous one?” This is an illustrative case, not a real patient.

By the end of this article you will know why that question matters less than it seems, how a glass tube and 20 minutes decide the antivenom, how much to give, and what to do if the antivenom itself causes a reaction.

1. India’s Snakebite Burden

Our farmer is not a rare case. He is the typical one. The tool opens its Evidence tab with these figures:

The scale of it: The Million Death Study, which is the largest nationally representative estimate, puts it at about 45,900 snakebite deaths a year in India (99% CI 40,900 to 50,900). The figure of 58,000 still widely quoted is an earlier estimate. Either way India carries close to half the world’s snakebite mortality. Of 310+ snake species here, 66 are venomous, and 4 of them account for 90% of envenoming: the Big Four.

Three more points used to sit under them in the tool, and are kept here:

• WHO NTD Status: Snakebite envenoming was recognised as a Neglected Tropical Disease (NTD) by WHO in 2017.
• Seasonality: Peak incidence during monsoon (June to September).
• Krait Nocturnal Bites: ~65.7% of snakebite deaths are from Common Krait, which bites sleeping victims at night. The bite is often painless and may go unnoticed.

“Why do the two death figures differ?” Because they are estimates made at different times. The Million Death Study counted deaths in a nationally representative survey; the 58,000 figure is an earlier estimate. Either way, the peak comes in the monsoon, when our farmer was bitten, and with the krait the victims are people asleep at night.

2. Do Not Wait to Identify the Snake

His brother wants to know whether the snake was poisonous. It is natural to ask, and the textbooks give long lists of differences between venomous and non-venomous snakes: head shape, pupils, fangs, bite marks. A common mistake is to wait for that answer. None of these features is reliable enough to decide treatment on, and the snake is rarely brought in anyway. The tool’s instruction is short: treat the syndrome in front of you, not the identification.

So we ask a different question: what is the venom doing to him? A painful, swollen limb and bleeding from the bite point to a haemotoxic bite. Drooping eyelids and descending weakness point to a neurotoxic one.

3. The Big Four, and the Gap in the Vial

Indian polyvalent ASV is made with the venoms of four species: the spectacled cobra, the common krait, Russell’s viper and the saw-scaled viper. It does not cover the hump-nosed pit viper (Hypnale hypnale), the banded krait or the king cobra.

This matters on our coast. The hump-nosed pit viper is common in coastal Karnataka. It causes AKI and coagulopathy, and Indian polyvalent ASV does not neutralise its venom, so its management is strictly supportive. And the olive keelback, a non-venomous snake very common near water, is often mistaken for a venomous one, which is a common reason for a frightened patient arriving with no envenoming at all.

4. The Glass Tube That Decides the Antivenom

The 20-minute whole blood clotting test (20WBCT) needs nothing from a laboratory. Collect 2 ml of freshly sampled venous blood into a new, clean, dry glass tube, not a plastic one, and leave it undisturbed for exactly 20 minutes. Then tilt it gently, once. If the blood runs out, the test is positive: the blood is not clotting. A firm clot is negative.

“How good is a test that simple?” Better than you might expect. A pooled meta-analysis puts it at 91% specific and 84% sensitive for coagulopathy, defined as an INR above 1.4. Read those two numbers carefully. A positive test is very likely to be real. But 84 per cent sensitivity means some patients with coagulopathy will still clot at 20 minutes, especially early. One clotted result on arrival does not rule out coagulopathy that has not yet declared itself, so the test is repeated on a schedule.

Our farmer’s blood runs out of the tube at 20 minutes. He has a haemotoxic syndrome with a positive 20WBCT.

5. How Much ASV?

The Indian national protocol gives the same loading dose for both syndromes: 10 vials in 200 ml normal saline IV over 1 hour. The maximum is 25 to 30 vials for a haemotoxic bite and 20 vials for a neurotoxic one.

“And for a child, a smaller dose?” No. The ASV dose neutralises the venom load, not the body weight. A snake injects the same venom into a child as into an adult, so a child receives the same dose as an adult.

6. When the Antivenom Itself Reacts

Reactions to ASV happen, so be ready before you start, not after. The tool lists three kinds:

• Early anaphylactic, 10 minutes to 3 hours after starting: adrenaline 0.5 mg IM (0.01 mg/kg in a child), stop the ASV for the moment, oxygen, IV hydrocortisone 200 mg and IV chlorpheniramine 10 mg, then restart the ASV slowly once he is stable.
• Pyrogenic, 1 to 2 hours after starting: rigors, fever and hypotension from pyrogen contamination during manufacture. Treat it exactly as an anaphylactic reaction.
• Late, serum sickness, 1 to 12 days after starting (mean 7): chlorpheniramine 2 mg IV every 6 hours for 5 days, and prednisolone 5 mg every 6 hours for 5 days if it has not settled in 24 to 48 hours.

Note the word “restart”. The reaction is treated, and the antivenom is then continued slowly; the venom has not gone away. Low-dose SC adrenaline (0.25 mg) given 5 minutes before ASV reduces early adverse reactions.

7. The Krait at Night

One last picture, because it is the one most easily missed. The common krait bites people asleep at night, and the bite is painless. The bite may go unnoticed. Colicky abdominal pain may be the first complaint, and the paralysis is delayed: the respiratory failure comes on during sleep and is found late. Its venom is pre-synaptic and responds poorly to neostigmine. Our farmer’s painful, swollen foot made a krait unlikely. A man found weak in the morning with drooping eyelids and no visible bite should make you think of one.

Back to Our Patient

He has a haemotoxic syndrome and a positive 20WBCT. He receives 10 vials of ASV in 200 ml normal saline over 1 hour, with adrenaline drawn up beside him. Nobody needed to know which snake it was. The 20WBCT is repeated on the tool’s schedule, and the decision to give more ASV is made on that, within the maximum of 25 to 30 vials.

Try This

An 8-year-old girl weighing 22 kg is bitten while playing near a haystack. Her 20WBCT is positive. The resident works out a dose of ASV by her weight. What should she get? Illustrative case.

Answer. 10 vials, the same loading dose as an adult, in 200 ml normal saline IV over 1 hour. The dose neutralises the venom load, not her body weight. If she reacts, her adrenaline dose is 0.01 mg/kg IM, about 0.22 mg.

Take-Home Points

• Treat the syndrome in front of you; do not wait to identify the snake.
• A positive 20WBCT is a reason for ASV; one clotted result on arrival does not rule out coagulopathy.
• The loading dose is 10 vials over 1 hour, and a child gets the same dose as an adult.
• Indian polyvalent ASV does not cover the hump-nosed pit viper, common in coastal Karnataka.
• Treat a reaction, then restart the ASV slowly; keep adrenaline ready before you start.

For the clotting failure the venom causes, and how it compares with other consumption coagulopathies, see Disseminated Intravascular Coagulation: The Evidence Behind the Pathway.

Declaration: the author built and maintains the tool. It is free to use. The figures in this article are those the tool carried in its Evidence tab on 5 November 2026, each from the source the tool names. The illustrative cases follow the tool’s rules; check the tool’s result for a real patient.

References

1. Ministry of Health and Family Welfare, Government of India. Standard Treatment Guidelines: Management of Snake Bite. NHM; 12 August 2017.
2. World Health Organization, Regional Office for South-East Asia. Guidelines for the Management of Snakebites. 2nd ed. WHO SEARO; 2016.
3. National Centre for Disease Control (NCDC). National Action Plan for Prevention and Control of Snakebite Envenoming (NAPSE). Ministry of Health and Family Welfare, Government of India; launched March 2024. [Snakebite envenomation was made a notifiable disease by MoHFW on 27 November 2024.]
4. Indian Academy of Pediatrics (IAP). National Treatment Guidelines: Snake Envenomation. NTG-005. IAP; 2023.
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10. Bawaskar HS, Bawaskar PH. Envenoming by the common krait (Bungarus caeruleus) and Asian cobra (Naja naja): clinical manifestations and their management in a rural setting. Wilderness Environ Med. 2004;15(4):257-266. PMID 15636376.