“there has to be a more merciful alternative”
Why does there have to be? Often the best practical solution still falls far short of perfect.
Falls short of perfect is a bit of an understatement. I will mention again that it also poses a danger to people and even pets who are not a threat to public health.
Strychnine poisoning is a very cruel way to die. It causes intense suffering. It is extremely inhumane. So yes a better way has to be found.