 [ Symptoms ] is there an ingredient in sudafed that is similar to an ingredient in bactrim that could cause an allergic reaction  is there an ingredient in behind the counter sudafed that is similar to an ingredient in prescription bactrim that could cause an allergic reaction like hives after ingestion over time [ Disease ] no there are no similar ingredients sudafed contains pseudoephedrine a decongestant it would be rare for this decongestant to cause hives bactrim is a sulfa drug that can definitely cause hives and a non hive skin condition often called a sulfa rash