Calculate the number 300

Because of an ear infection, Little Johnny, had to go to the pediatrician. The doctor directed his comments and questions to Little Johnny in a professional manner. When he asked Little Johnny, "Is there anything you are allergic to?" Little Johnny nodded and whispered in his ear. Smiling, the pediatrician wrote out a prescription and handed it to Little Johnny's mother. She tucked it into her purse without looking at it.
As the pharmacist filled the order, he remarked on the unusual food- drug interaction Little Johnny must have. Little Johnny's mother looked puzzled until he showed her the label on the bottle. As per the doctor's instructions, it read, "Do not take with broccoli."