How often should the contents of first-aid boxes be replaced?

Although there is no specified review timetable, many items, particularly sterile ones, are marked with expiry dates. They should be replaced by the dates given and expired items disposed of safely. In cases where sterile items have no dates, it would be advisable to check with the manufacturers to find out how long they can be kept. For non-sterile items without dates, it is a matter of judgement, based on whether they are fit for purpose.