Illness doesn't respect the schedule. The medicine was given at one house and the next dose is due at the other — that handover is where mistakes happen, in every family, not just separated ones.
What was given, how much, when, by whom. That one habit removes the worst risk: a double dose because nobody was sure.
When custody changes mid-course, the other parent needs three things: what the medicine is, when the last dose was, when the next one is due.
"Dr Chen, Thursday 2.15 — can you take her?" asked in a message beats a phone call nobody remembers the same way.
Allergies, conditions, the regular doctor. Not in one parent's head.
Doses are logged with who and when, a course carries across the custody change on its own, and appointment requests come with a confirm button — so the sick week runs on the record, not on memory.