$mandrill = Mandrill($my_api_key); breaks plugin

I’m looking at the How-Tos for How to send emails from within your plugins. “if you need Mandrill Powers, we have included a full-featured PHP class called Mandrill… To use it, just instantiate an object passing your API key, and make the calls: $mandrill = Mandrill($my_api_key);”

If I have $mandrill = new Mandrill(‘mykey’); in a plugin (where mykey is my API key, of course), when I activate my plugin I get “Plugin could not be activated because it triggered a fatal error.” “Fatal error: Class ‘Mandrill’ not found…”

https://www.ads-software.com/plugins/wpmandrill/