That's the name of the cocktail. It doesn't actually contain penicillin*. They use a rim dipped in sparkly sugar and a combination of Azithromycin, Doxycycline, and Erythromycin which is both tasty and helps treat Chlamydia which you get from drinking Clamato**.
* - True
** - Made up for comedic effect.***
*** - I've reached the conclusion that most of my humor**** would now be called out as misinformation.
**** - Humour in Canada, England, Scotland, Ireland, Australia, New Zealand and other Commonwealth nations*.