Antivenom Injection

Indications

Snake Venom Antiserum (antivenom) is an injection used to treat poisoning (envenomation) after a bite from a venomous snake. In Bangladesh, polyvalent antivenom is made against the venoms of the common dangerous snakes, such as cobras, kraits and Russell's viper. It is given when a bite causes signs of poisoning, such as drooping eyelids, weakness, difficulty breathing or swallowing, bleeding, blood that does not clot, severe spreading swelling, or kidney problems. It is used only in hospitals and health centres.

How It Works

Antivenom contains antibodies (or antibody fragments) taken from horses that were immunised with small, safe amounts of snake venom. When injected, these antibodies bind to venom in the blood and tissues and neutralise it before it can do further damage. It cannot reverse damage that has already happened, so early treatment is important.

Dosage and Administration

It is given by a doctor or nurse into a vein, by slow injection or infusion, in a facility able to treat allergic reactions. The dose depends on the severity of poisoning and the national snakebite treatment guideline, not on body weight; children receive the same dose as adults. Further doses may be given if signs of poisoning continue. Some doctors give medicine such as Adrenaline before the dose to lower the risk of reaction.

Interactions

No drug interactions of practical importance are known. Other treatments such as Neostigmine with Atropine for nerve paralysis, breathing support, dialysis, tetanus vaccine and antibiotics may be given alongside it.

Contraindications

• There is no absolute contraindication when poisoning is life-threatening.
• People with a previous reaction to horse serum or antivenom, or with asthma or allergies, need extra caution and close monitoring.
• It is not given to people bitten by a non-venomous snake or without signs of poisoning.

Side Effects

Early reactions, within minutes to hours, are common and include itching, hives, fever, shivering, nausea, vomiting, wheezing and low blood pressure; severe allergic reactions (anaphylaxis) can occur. Late reactions (serum sickness) may appear 5 to 24 days later with fever, rash, joint pain and swollen lymph glands.

Tell the health worker immediately if you feel itchy, breathless, dizzy, or develop swelling of the face during or after the infusion. After going home, seek medical help for fever, rash, joint pain, new bleeding, reduced urine or new weakness.

Pregnancy and Lactation

Snakebite poisoning is dangerous for both mother and baby, so antivenom should be given in pregnancy when needed. Breastfeeding can usually continue; follow the doctor's advice.

Precautions and Warnings

First aid: keep calm and still, immobilise the bitten limb, remove rings and tight items, and go to a hospital quickly. Do not cut the wound, suck it, apply tight tourniquets, ice or herbs, or wait for traditional healers. The patient should be observed for at least 24 hours after treatment.

Overdose

There is no specific overdose effect, but larger amounts increase the risk of allergic and serum reactions, which are treated by the hospital team.

Therapeutic Class

Antivenom (immune sera and immunoglobulins).

Storage

Hospital medicine: store as directed on the pack. Liquid antivenom is usually kept in a refrigerator at 2 to 8°C and must not be frozen; freeze-dried antivenom is usually stored below 25°C. Keep out of the reach of children.