Actually I've found Delsym doesn't agree with a lot of people in high doses, including myself. I'm talking horrible trip for 12 hours filled with a hurling adventure. I believe it was the "plastics" in Delsym that didn't agree with me but I am unsure. I wasn't willing to repeat and just the sight of the stuff turns my stomach now.
Like tricomb said don't use what you have. I know 100mg doesn't sound like much but trust me once you're into it you'll know even the 1st plat. isn't "mild". In fact, most of my bad trips happened on that plateau. These were not bad in the way shrooms/acid can be, more of an overall feeling of begin shitty. Kinda like opiate withdrawal times 5.
The only "safe" way to robotrip it to extract the DXM from all (most) of the inactive substances in product where DXM is the only active ingredient or obtaining pure DXM powder. If you can not to that the bare minimum would be using a product that only contains DXM as an active, but be warned the "inactives" in the syurp/pills you use can and will cause you problems at higher doses. For some people it is not as bad as others but everyone experiences some difficulty.
Edit: For brands if you're in the states I've found these two to be the bee knees, but you should double check the package for yourself to ensure there is only DXM and no other actives:
- For syrup I used Roboitussin "long acting cough" which IIRC is about 350-370mg of DXM per

z. You should double check that figure by the way

. This tastes like a horses ass but it only has DXM as an active and it is available in most places I have looked. It is a little thick as well, and contains a small amount of alcohol.
- Gelcaps: Roboitussin Gels which are 10mg of DXM per gelcap iirc. I think it contains 300mg of DXM per bottle of gelcaps. These work okay but take longer to kick in than the syrup because they release slower. This also changes the feel of the trip itself (something to do with the DXM to DXO ratio in the body). My first trip was with these but later on I found them hard to gag down so I switched to syrup.
Those are the only two I ever used aside from the one time with Delsym. I found the syrup to have the least side effects, but even it caused the worse smelling gas I've ever had and constipation. If I were to use DXM again to obtain a trip I would extract the DXM though, chugging down syrup is just too hard for me these days because I know its going to be hell for a couple of days after the trip due to the inactives not agreeing with me. There is no way ingesting all that crap can be good for your body and I always felt like I'd been in a train wreck for at least a few days after a 2nd-3rd plat. trip.