A brief overview of snakebite in Zimbabwe and how antivenom is produced.

1. v
Website: www.datis.uz.ac.zw
Phone: 04 293 3452

2. About Snake Antivenom…
Dr Dexter Tagwireyi
BPharm(Hons), MAppSci(Tox), DPhil
Senior Lecturer & Director
Drug and Toxicology Information Service
College of Health Sciences
University of Zimbabwe

3. 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…

4. A LITTLE “EXTRA”

5. COMPARE AND CONTRAST
v
Tail “Thickness”
“Claw Size”
Parabuthus sp. Scorpionidae

6. 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

7. Clinical Patterns of Snake Venom
• Broadly speaking, there are four
main types of envenoming
– Cytotoxic Envenoming
– Haemorrhagic Envenoming
– Neurotoxic Envenoming
– Myotoxic Envenoming

8. Cytotoxic Envenoming
• Painful and progressive
swelling
• Blood-stained tissue
fluid
• Blistering
• Bruising
• Necrosis/gangrene

9. Neurotoxic Envenoming
• Little to no swelling
• Descending Paralysis
• Ptosis
• Vomiting
• Profuse, stringy
saliva
• Dyspnoea
• Dysphagia

10. Haemorrhagic Envenoming
• Bleeding from
– Gums
– GIT
– GUT
– Recent wounds
– Partly healed wounds

11. Antivenom
• Only effective specific treatment or antidote
for snakebite
• Produced by hyperimmunizing large domestic
animals
• Antibodies
• Two types
– Monovalent/monospecific
– Polyvalent

12. Antivenom Production
Lyophilized
Venom Injected
Bleeding
Processing

14. 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

15. 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

16. Indications for Antivenom Use
WHO (2010), Guidelines for the Prevention and Clinical
Management of Snakebite in Africa, WHO Publications, Geneva

17. 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

18. Objectives Met?
• Do participants now have an appreciation of
snake venom and antivenom with reference to
Zimbabwean venomous snakes?

19. References
• WHO (2010), Guidelines for the Prevention
and Clinical Management of Snakebite in
Africa, WHO Publications, Geneva

20. May God Bless You All