Volume 179 - Issue 8
Latrodectism: a prospective cohort study of bites by formally identified redback spiders
Author: Geoffrey K Isbister
Med J Aust 2003; 179 (8): 455-456. || doi: 10.5694/j.1326-5377.2003.tb05641.x
Published online: 20 October 2003
Published online: 20 October 2003
Geoffrey K Isbister
Clinical Envenoming Research Group, University of Newcastle, Newcastle Mater Misericordiae Hospital, Locked Bag 7, Hunter Region Mail Centre, NSW 2310 gsbiteATferntree.com
In reply: We thank Wiener for his comments on our study. Although we challenge the use of intramuscular redback spider antivenom (RBS AV) in the article, we only suggested that the use of intramuscular antivenom needs review and that randomised controlled trials comparing intravenous and intramuscular RBS AV should be undertaken. Two such trials, in Western Australia and Newcastle, are currently in progress.
There are no pharmacokinetic studies of RBS AV, but studies of other antivenoms suggest that the intramuscular route is less effective.1 In Tunisia, the intramuscular use of scorpion antivenom, which is also an F(ab')2 antivenom, similar to RBS AV, has been questioned for similar reasons.2,3 Studies in a rabbit model demonstrated that intramuscular antivenom induced only partial and delayed neutralisation of circulating toxins.3 More importantly, in a study of scorpion stings of children, the intramuscular administration of antivenom had far less effect on plasma venom concentrations and patient recovery times.2
We do not dispute that repeated doses of antivenom may be required, but the implication that only an initial dose was used in our study is incorrect. Half of the treated patients required repeat doses (6 ampoules in one patient). In a recent series of four patients with redback spider bites, intramuscular antivenom was ineffective, even though three patients received two or three ampoules. Subsequent intravenous antivenom was effective in all cases.4 There is no evidence that appropriately administered intravenous RBS AV (diluted in 200 mL of normal saline, over 20–30 minutes) is less safe than intramuscular antivenom. There is insufficient reason to prevent the use of intravenous antivenom if it is shown to be more effective than intramuscular antivenom. Although it is too early to change recommendations for the administration of RBS AV, it is essential that controlled trials be done.
References
- Riviere G, Choumet V, Audebert F, et al. Effect of antivenom on venom pharmacokinetics in experimentally envenomed rabbits: toward an optimization of antivenom therapy. J Pharmacol Exp Ther 1997; 281: 1-8. CACHCFGJ
- Krifi MN, Amri F, Kharrat H, El Ayeb M. Evaluation of antivenom therapy in children severely envenomed by Androctonus australis garzonii (Aag) and Buthus occitanus tunetanus (Bot) scorpions. Toxicon 1999; 37: 1627-1634. CACJIGJE
- Krifi MN, Miled K, Abderrazek M, El Ayeb M. Effects of antivenom on Buthus occitanus tunetanus (Bot) scorpion venom pharmacokinetics: towards an optimization of antivenom immunotherapy in a rabbit model. Toxicon 2001; 39: 1317-1326. CACJEBGE
- Isbister GK. Failure of intramuscular antivenom in redback spider envenomation. Emerg Med 2002; 14: 436-439. CACFAIHA