Hi Thanks for posting your query on HCM. I appreciate your concern for the safety of the prescribed medications. Both of the prescribed drugs may cause allergic reactions which are manifested in the form of itching, rash, difficulty in breathing, etc. But because of the sulfur content, Bactrim DS is more likely to cause severe itching, rash and other side effectgs like painful ulcers in the oral cavity. So, in view of troublesome severe generalized itching, consult your treating doctor so as to use alternate antibiotic. Avoid driving while taking Benadryl as it may cause drowsiness and lack of concentration. If needed you may use Cetrizine which causes less drowsiness. Avoid taking sulfur containing drugs in future. Hope this answers your query. A feed back is appreciated.