I have looked into a sedative for trying to trap a dog. We rescued a feral colony of cats and cannot get the dog that has lived with them for at least 4 years. The problems that I have been told in giving a sedative in the food is that you cannot get a correct doseage which could be fatal. Dose is per animal weight. Being a kitten makes that even more unpredictable. Also, IF sedative is given, you have to keep eye contact on the animal. They will become disoriented and may dart into traffic or injure themselves in some way. Very exposed to any natural predator as well. We abandoned this idea.
In your other post LDG gave very sound advice. They will respond to food and a schedule. It does not matter the time of day be it morning or evening. They will follow your lead. I got a kitten over weekend this way. I put the food in the carrier and as soon as their head was in the door I scooped them in and closed the door quickly. They were clueless as to what happened. Kittens are great that way.
You are doing an awesome thing. Keep trying and it will work out.