A common reason why a child may get overly excited, run around, and otherwise misbehave is due to lack of sleep. Try monitoring the total sleep time in hours (nighttime plus daytime), compare it to the recommended sleep time, and ensure that this common root cause of many problems is eliminated.
We can watch a child’s behavior during the day ...
Depending on how old said toddler is, I would try to give him some time during the weekdays to run around, to get that excess energy out.
Aside from that I recommend closing and locking the bathroom door until you’ve applied the cream or maybe grab the book and the bottle and keep it with you so that he understands its time to relax.
I have a 2yo and she does something similar.
I try to minimize the opportunity for escape by closing doors and preparing everything beforehand, and then I lure her by encouraging to help me. I offer her the cream and ask her where she wants to put it on.
They're usually really interested in helping, so framing it as something fun and exciting to help with is ...