I have dosed pseudoephedrine hci, guaifenesin, and dextromethorphan hbr. I also took 2 10/650 vicodin. Is this safe I took about 3.5 fluid ounces of Robitussin cf, which is what contained all of the ingredients listed. Is this combination potentially harm

No. 3.5 ounces of Robitussin (guaifenesin) is an excessive dose in and of itself (usual dose is 15-30 ml, which is 1/2-1 oz). Combining this with 2 vicodin increases the chance of toxic effects. Follow instructions on otc medications if you want to use them safely, and tell the doctor prescribing the vicodin about your use of other medications with it.
According . According to drugs.Com, there are no interactions listed for Robitussin (guaifenesin) CF and vicodin. However, if you are not feeling well, you should contact you doctor to discuss.