You may write a note to the school requesting that your child be given medication. If you have already informed the teachers of your child's illness or symptoms, it is unnecessary to explain this again. In this case you only need to write what medication should be given, and when it should be administered.
If your preschool has a designated form to be filled out when making a request for medication administration, you do not need to write a note in the renrakucho notebook. In addition, every school has its own medication policies in place, such as only allowing medications received from a medical facility, so you should ask your school about its medication policies.
Some medical facilities will allow you to choose between medications that are administered twice a day or three times a day. You may ask your regular doctor about this.
Conversational flow and useful expressions
Medication administration request
In this case, it is not appropriate to use 「ありがとうございます」(arigato gozaimasu), which is a straightforward way of saying "thank you." Instead, you should use「よろしくお願いします」(yoroshiku onegai shimasu) which contains elements of both "please" and "thank you", and is often used to make requests and thank someone in advance for something.