Pharmacology, Toxicology and Addiction MedicineTier 2Approach to a presentation

Poisonings - snake bites

Red flags

Signs of systemic envenomation (coagulopathy/bleeding, neurotoxicity - ptosis, ophthalmoplegia, bulbar/respiratory weakness, myotoxicity - muscle pain and dark urine from rhabdomyolysis) indicate a medical emergency requiring urgent antivenom consideration
Respiratory failure from neurotoxic envenomation can progress rapidly and requires close monitoring for early intubation if developing

Differential by mechanism

Systemic envenomation (coagulopathy, neurotoxicity, or myotoxicity depending on snake species - the primary concern)

Local envenomation only (pain, swelling, bruising without systemic features)

Dry bite (no venom injected - occurs in a proportion of bites, but cannot be assumed without adequate observation and testing)

Anxiety/panic reaction to the bite itself, distinct from true envenomation, though should not be assumed without appropriate exclusion of envenomation first

Focused history

Time and circumstances of bite, description of the snake if possible (without risking further exposure to identify it), symptom onset and progression (local pain/swelling, systemic symptoms - visual disturbance, difficulty swallowing/breathing, muscle pain)
First aid measures already applied (pressure immobilisation bandaging, if used and how correctly applied) and time since bite

Focused examination

Local bite site (fang marks, swelling, bruising extent), neurological examination specifically for early ptosis/bulbar weakness (an early, sensitive sign of neurotoxic envenomation), vital signs
Serial examination is essential given envenomation effects can evolve over hours - a single normal early assessment does not exclude developing envenomation

Investigation strategy

Coagulation studies (looking for venom-induced consumption coagulopathy), creatine kinase (myotoxicity), and urinalysis (myoglobinuria) form the core laboratory panel for systemic envenomation assessment
Serial testing is required given the evolving nature of envenomation effects over the hours following the bite

Management

Pressure immobilisation bandaging applied firmly over the bite site and extending to immobilise the whole limb, maintained until antivenom is available or envenomation is excluded - this first aid measure slows lymphatic spread of venom and should not be removed prematurely
Antivenom for confirmed or strongly suspected systemic envenomation, matched to the relevant snake species/region where possible, given with anaphylaxis precautions/readiness given antivenom's own allergic reaction risk
Supportive care for specific complications (fresh frozen plasma for coagulopathy is generally deferred until after antivenom, since venom continues consuming clotting factors until neutralised)

Traps

Removing pressure immobilisation bandaging prematurely before envenomation has been excluded or antivenom given - this can cause a sudden systemic venom bolus

Assuming a dry bite too early without adequate observation period and serial testing, given the evolving nature of envenomation

Giving fresh frozen plasma before antivenom for coagulopathy - clotting factors will simply continue to be consumed until the venom itself is neutralised

Talk track

"We're going to keep the pressure bandage on your leg for now, since removing it too soon could let venom move through your body faster - we need to watch you closely with blood tests over the next several hours to see whether the venom has caused any effects, since these can take time to appear even if you're feeling okay right now."

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