Which medically significant venomous snakes occur in the Philippines and what is the appropriate emergency management for their bites?

Medically Significant Venomous Snakes in the Philippines and Emergency Management

The Philippines has two WHO Category 1 medically important venomous snake groups requiring immediate emergency activation and rapid transport to a hospital: the Philippine cobra (Naja philippinensis) and Samar cobra (Naja samarensis) which cause severe neurotoxicity with minimal local signs, and Trimeresurus pit vipers (T. flavomaculatus and T. mcgregori) which cause coagulopathy and local tissue damage. 1, 2, 3

Medically Significant Species

Cobras (Elapidae Family)

• Philippine cobra (Naja philippinensis) causes severe neurotoxicity with rapid onset—respiratory paralysis can develop within 30 minutes of the bite in some cases 4
• Distinctive clinical picture shows prominent neurotoxicity with minimal local tissue damage—14 of 39 patients had systemic symptoms with no local swelling 4
• Samar cobra (Naja samarensis) produces similar neurotoxic effects but can also cause extensive local cytotoxic damage requiring surgical debridement 1
• Both species can spit venom into eyes, requiring specific management 1

Pit Vipers (Viperidae Family)

• Green pit vipers (Trimeresurus species including T. flavomaculatus and T. mcgregori) are important for their high incidence of bites in the Philippines 5
• These venoms cause pseudo-procoagulant activity leading to net anticoagulation through fibrinogen depletion and inhibition of clotting factors fIXa and fXa 2
• Result in weak, transient fibrin clots contributing to bleeding complications 2

Sea Snakes

• Sea snake bites occur in the Philippines but are less common than in Malaysia 5

Immediate Field Management

Universal First Aid (All Philippine Snake Bites)

• Activate emergency medical services immediately for any venomous or possibly venomous snake bite 6, 7
• Remove all rings, watches, and constricting jewelry immediately before swelling develops to prevent ischemic injury 6, 8, 7
• Immobilize the bitten extremity completely and keep it below heart level 8
• Minimize patient exertion during transport—walking or physical activity increases systemic venom absorption through lymphatic flow 6, 8

Critical Species-Specific Distinction

• For cobra bites (neurotoxic): Apply pressure immobilization bandaging at 40-70 mm Hg in upper extremity or 55-70 mm Hg in lower extremity around the entire length of the bitten limb 6, 8, 9
• The bandage should be comfortably tight and snug but allow a finger to be slipped under it 6
• For pit viper bites (vasculotoxic/cytotoxic): Do NOT use pressure immobilization as it may worsen local tissue damage by trapping venom at the bite site 8, 9, 7

Harmful Practices to Avoid

• Do NOT apply suction devices—they are ineffective for venom removal and may cause tissue injury 6, 7
• Do NOT apply tourniquets—they can worsen local tissue injury 6, 7
• Do NOT apply ice—it has unproven benefits and may cause tissue injury 6, 7
• Do NOT apply electric shock—it is ineffective and potentially harmful 6, 7

Hospital-Based Definitive Treatment

Antivenom Administration

• Philippine Cobra Antivenom (PCAV) is the only locally-produced antivenom available in the Philippines, raised against N. philippinensis venom 1, 3
• PCAV successfully treats N. philippinensis envenomation with supportive management 1
• PCAV cross-neutralizes N. samarensis venom but requires approximately two-fold higher doses compared to N. philippinensis envenomation 3
• Four out of five confirmed N. samarensis cases were successfully treated with PCAV 1

Alternative Antivenoms for Pit Vipers

• Thai Red Cross Society polyvalent antivenom effectively cross-neutralizes Trimeresurus pit viper venoms and rescues fibrinogen clotting better than monovalent antivenom 2
• This represents a viable option for areas with high pit viper envenomation risk where specific antivenom is unavailable 2

Monitoring and Admission

• Admit all suspected cobra bite patients for minimum 48 hours with continuous monitoring—neurotoxicity onset can be delayed up to 13 hours despite minimal local findings 8, 9
• Be prepared for rapid intubation—respiratory paralysis can develop within 30 minutes in severe cases 4
• Monitor for coagulopathy in pit viper bites through serial coagulation studies 2

Critical Clinical Pitfalls to Avoid

Cobra Envenomation

• Never assume no envenomation based on lack of local symptoms—cobra bites produce minimal to no local tissue damage despite life-threatening systemic neurotoxicity 8, 9, 4
• Cardiotoxicity and reliable nonspecific signs of envenoming are absent in Philippine cobra bites 4
• Three patients in one series developed necrosis despite the predominantly neurotoxic nature, so local tissue damage can still occur 4

Pit Viper Envenomation

• Do not use pressure immobilization techniques developed for neurotoxic snakes on pit viper bites—this worsens local tissue injury 8, 9, 7
• Recognize that pseudo-procoagulant activity leads to net anticoagulation, not thrombosis 2

General Management Errors

• Delaying transport to attempt ineffective field interventions wastes critical time—time to antivenom is the most important prognostic factor 8
• Failing to remove constricting items like rings leads to ischemic injury as swelling progresses 6, 8, 7
• Using PCAV for N. samarensis at standard N. philippinensis doses may result in treatment failure—double the dose 3