Which of the following substances is the most common cause of anaphylaxis?

Penicillin and other antibiotics are the most common causal agents for anaphylaxis. Authorities estimate penicillin produces an allergic or anaphylactic reaction 1 out of every 10,000 times it is used and causes an estimated 500 deaths per year. By contrast, bee stings are responsible for less than 100 deaths annually. Anaphylactic reactions to aspiring and fungi and molds are infrequent and therefore not common causal agents.