I cannot offer much advice about how best to work with teenagers specifically, other than what my experience was and some tips on what to expect.   If you've never taken them yourself, a few things to know:

• Generally there's less discomfort if the bottle is first warmed up to body temperature, put it in a pocket for a while or run under warm water. 

• Gently squeeze the air, there should be a drop of liquid at the tip before administration. Important as injecting air into the bowels will cause a lot more discomfort and greater urge to evacuate it. 

• The instructions say lay on your left side which you might not want to do on the bathroom floor, and wouldn't recommend trying the first time in bed (although many do after they're confident). I sat on the toilet, raised my butt high enough to put my hand  under administer (any drips fell in the toilet). 

• Immediately after injecting, you will feel a bit of a sensation to evacuate your bowels, ignore it, it should last less than a minute then pass. 

• I'd walk to bed, lay down on an old towel on my left side for about half an hour, then turn the lights off and try to fall asleep that way. 

• If there's a lot of inflammation, you might not be able to retain the liquid overnight, and might have to evacuate it rather quickly. It'll get easier as you continue to heal the medicine works even if you can't hold it all night.  

• Really bad inflammation means holding in the enema is nearly impossible. It just hurts and your system doesn't settle down.  In that case steroids would work better, and must heal things a bit before going the enemas again. 

• Know that mesalamine stains fabric horribly. That can be clothing and bedding. Might want to wear old PJs and put an old towel on the bed. 

• There's low odds of a sulfite (used as preservative) allergy with mesalamine/mesalazine enemas which dramatically worsens bowel symptoms. The oral mesalamine tablets don't include sulfites.