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?
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".