You milk the cat?

Listening to Radio One this was on:
A vet gave a woman some cream for her cat as it was ill and needed some antibiotics. As he was out of his usual labelled stock he gave her one that was also used for cows as it's cheaper, it therefore has instructions for use on cows written on the tube.
After a week of using the cream she brought the cat back and the vet said the cat is fine and you can stop using the cream now.
“Great” she said “I can have a good cup of tea again”.
“What do mean?” asked the vet.
“Well I like milk in my tea and on the tube for the cream it says after use throw out all milk for the next 48 hours.”