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".
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?