This smaller sized, long lasting reusable gel ice pack for medicines fits our small medicine cases.  It can stay cool for a good 6 hours or longer depending on the temperature it is being exposed to and how long etc.
 
Durable Nylon exterior
Freeze 2-3 hours prior to use
According to our test data this ice pack can stay cool at least 6 hours when the ambient temperatures were 23-25℃ / 73.4 – 77℉
Small size: Measure 2.4" x 4"