Pharmacology, Toxicology and Addiction MedicineTier 2Approach to a presentation

Poisonings - spider bites

Red flags

Signs of severe systemic envenomation (autonomic disturbance, severe pain, significant sweating/hypertension with certain spider species) or evolving significant local tissue necrosis require prompt specific management
Anaphylaxis to the bite itself (distinct from venom toxicity) should also be assessed for in any acute presentation

Differential by mechanism

Local reaction (pain, redness, swelling at the bite site - the most common presentation for most spider bites)

Systemic envenomation (species-dependent - some spiders cause significant systemic autonomic/neurotoxic effects, others predominantly local tissue effects)

Secondary infection (a bite site complication that can develop after the initial presentation, sometimes confused with ongoing envenomation)

Necrotic arachnidism (significant local tissue necrosis, associated with specific spider species in some geographic regions)

Focused history

Circumstances of the bite, spider description/identification if possible, geographic region (relevant given significant species variation in clinically important spiders), symptom onset and progression (local pain evolution, any systemic symptoms - sweating, muscle pain, autonomic symptoms)
Time since bite, given some systemic envenomation syndromes evolve over hours

Focused examination

Bite site characteristics (puncture marks, surrounding erythema/swelling, any developing necrosis), systemic assessment for autonomic/neurotoxic features where a clinically significant species is in the differential
Serial reassessment given the evolving nature of some envenomation syndromes

Investigation strategy

Generally a clinical diagnosis; specific antivenom availability and significant systemic envenomation syndromes vary by region and spider species, so local toxicology/poison information service consultation is valuable for guiding species-specific management
Wound assessment/monitoring for secondary infection or progressive necrosis in the follow-up period

Management

Local reaction: symptomatic treatment (analgesia, ice, wound care) is generally sufficient for the majority of spider bites
Significant systemic envenomation: species-specific management, which may include specific antivenom where available and indicated, alongside supportive/symptomatic treatment for autonomic or pain symptoms
Early surgical/specialist referral if significant progressive local necrosis develops

Traps

Assuming all spider bites are dangerous and over-investigating/over-treating minor local reactions, which represent the large majority of presentations

Under-recognising a genuinely significant systemic envenomation in a region/species where this is a real risk, by not seeking specific local toxicology guidance

Missing secondary wound infection developing after the initial bite, which can be mistaken for ongoing venom effect if not specifically reassessed

Talk track

"Most spider bites cause only local pain and swelling that settles with simple pain relief and wound care - we'll keep an eye on you for any signs of a more significant reaction, and if we're not sure exactly what kind of spider was involved, we can check with the poisons information service for specific advice."

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