Since you have to play trough the game twice to unlock all achievements, you will probably make significant progress towards this so boosting early might not be worth it.
You will find a lot of medkits in the world. However you will most likely not use that many of them during your playtrough, especially if you play on easy and/or avoid combat as much as possible.
You can only use a medkit if you have damage. What I would do is every time right after a fight I would use a medkit, unless my stock was low. This strategy will definitely unlock the achievement for you within one/two playtroughs.
Alternatively you can stand next to an enemy and spam your medkits until you are out and then reload checkpoint. Reloading checkpoint does not reset your progress.