My dd [5] had to have 2 courses after becoming terribly constipated. She was so bad I took her to A&E as she couldn't stand straight
The first course the hospital only gave her was 2 sachets & while it worked, it didn't clear her out, iykwim..so we were back to square one after 3 days.
Then they gave her a maintenance dose.
Day 1 - 1/2 sachet (as soon as we got home - at 10pm)
Day 2 - 1 (early am, kept off school but mainly due to pain)
Day 3 - 1 & 1/2 (1 before school, 1/2 after)
Days 4/5/6/7 2 sachets. (1 before school, 1 after)
It finally worked & worked well. Dd didn't suddenly get the urge to go, but I tried to instill in her that she should listen to her body, thankfully her teacher was very kind & gave her permisson to just up & leave the room for the toilet when she needed [the toilet being conveniently situated next to her class]
Dd didn't have any accidents, but towards the end it did get (tmi) quite runny & so she would have if she didn't go when she needed to.
Thankfully we have had no repeats! Hope he is better soon.