Experience of using expired lyophilized snake antivenom during a medical emergency situation in Lao People's Democratic Republic-A possible untapped resource to tackle antivenom shortage in Southeast Asia

Objectives: To evaluate the safety and efficacy of expired lyophilized snake antivenom of Thai origin during a medical emergency in 2020/2021 in Lao People's Democratic Republic. Methods: Observational case series of patients with potentially life-threatening envenoming who consented to the administration of expired antivenom between August 2020 and May 2022. Results: A total of 31 patients received the expired antivenom. Malayan pit vipers (Calloselasma rhodostoma) were responsible for 26 (84%) cases and green pit vipers (Trimeresurus species) for two cases (6%). In three patients (10%) the responsible snake could not be identified. Of these, two presented with signs of neurotoxicity and one with coagulopathy. A total of 124 vials of expired antivenom were administered. Fifty-nine vials had expired 2-18 months earlier, 56 vials 19-36 months and nine vials 37-60 months before. Adverse effects of variable severity were observed in seven (23%) patients. All 31 patients fully recovered from systemic envenoming. Conclusions: Under closely controlled conditions and monitoring the use of expired snake antivenom proved to be effective and safe. Discarding this precious medication is an unnecessary waste, and it could be a valuable resource in ameliorating the current shortage of antivenom. Emergency use authorization granted by health authorities and preclinical testing of expired antivenoms could provide the support and legal basis for such an approach.