snakebite in zimbabwe: an overview of snake antivenon
TRANSCRIPT
About Snake Antivenom…
Dr Dexter TagwireyiBPharm(Hons), MAppSci(Tox), DPhil
Senior Lecturer & DirectorDrug and Toxicology Information Service
College of Health SciencesUniversity of Zimbabwe
Objectives
• To give participants an appreciation of snake venom and antivenom with reference to Zimbabwean venomous snakes
• To throw in a little “extra” for your interest…time permitting…
A LITTLE “EXTRA”
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COMPARE AND CONTRAST
Tail “Thickness”“Claw Size”
Parabuthus sp. Scorpionidae
Snake Venom
• Primary function of snake venom– Help snake immobilize prey– Help snake digest prey
• Composed of numerous toxic & non-toxic components– >90% of dry weight is protein– Enzymes and polypeptide toxins
lead to clinical effects
Clinical Patterns of Snake Venom
• Broadly speaking, there are four main types of envenoming– Cytotoxic Envenoming– Haemorrhagic Envenoming– Neurotoxic Envenoming– Myotoxic Envenoming
Cytotoxic Envenoming
• Painful and progressive swelling
• Blood-stained tissue fluid
• Blistering• Bruising• Necrosis/gangrene
Neurotoxic Envenoming
• Little to no swelling• Descending Paralysis• Ptosis• Vomiting• Profuse, stringy
saliva• Dyspnoea• Dysphagia
Haemorrhagic Envenoming
• Bleeding from – Gums– GIT– GUT– Recent wounds– Partly healed wounds
Antivenom
• Only effective specific treatment or antidote for snakebite
• Produced by hyperimmunizing large domestic animals
• Antibodies• Two types– Monovalent/monospecific– Polyvalent
Antivenom Production
Lyophilized
Venom InjectedBleeding
Processing
Antivenom Use
• Things to remember about use– All commercial antivenoms carry risk of potentially
dangerous early anaphylactic reactions– Not all bites result in envenomation• Non venomous snakes• “Dry” bites
– Antivenom very expensive, limited shelf life– Some species of snake have no antivenom – Some antivenoms are specific
Antivenom Use
• Most effective when given IV• Can be given at injection rate of 5ml/minute
or diluted in isotonic fluid and infused over 30-60 minutes
• If IV impossible, IM (not ideal) at different sites (anterior and lateral aspects of thigh)
• In children intraosseous• Other issues
Indications for Antivenom Use
WHO (2010), Guidelines for the Prevention and Clinical Management of Snakebite in Africa, WHO Publications, Geneva
Adverse Effects
• Early reactions– Begin 3-60 minutes after starting IV administration– Cough, tachycardia, itching (esp. scalp), urticaria,
fever, vomiting, headache– >5% develop systemic anaphylxis• Hypotension, bronchospasms, angio-oedema
• Pyrogenic reactions (1-2 hours)• Late reactions (4-24 days)– Serum sickness type (itching, urticaria, fever,
arthralgia, etc
Objectives Met?
• Do participants now have an appreciation of snake venom and antivenom with reference to Zimbabwean venomous snakes?
References
• WHO (2010), Guidelines for the Prevention and Clinical Management of Snakebite in Africa, WHO Publications, Geneva
May God Bless You All