Sherlock asks his would-be sponsor about taking diphenhydramine to counteract poisoning. He later tells Watson that diphenhydramine is a hallucinogenic drug that has been outlawed in some countries. Diphenhydramine is an antihistamine, the main ingredient in OTC Benadryl
Lisa Edelstein, who guest stars in this episode, previously acted in House (2004), which itself was based on Sherlock Holmes.
The battery in the pager would have been flat long before the pager was accidentally dialled. Therefore the pager would no longer have been able to detonate the bomb. No pager had a battery which would have kept the pager going for 4 years.